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Homework question on chemically defined medium

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Why would the following medium not be considered a chemically defined medium:

Glucose, 5 grams (g); NH4Cl, 1g; KH2PO4, 1g; MgSO4, 0.3g; yeast extract, 5g; distilled water, 1 litre

I am unsure why it is not a chemically-defined medium considering all measurements and grams are given and such is required for it to be one. Therefore I am unsure why it would not be a chemically defined medium.


A chemically defined medium is, according to this Wikipedia article:

… a growth medium suitable for the in vitro cell culture of human or animal cells in which all of the chemical components are known.

Four of the five components fit this criterion precisely, as they are chemical formulae (and of course a common name for a compound whose formula is well known).

However, even though you know exactly how much yeast extract was added to the medium, you do not know its exact chemical composition. To be sure, assays of the chemical composition of yeast extract have been run, and one could come up with approximations of it's makeup. But the bottom line is that there is no precise chemical formula for yeast extract as there are for the other components of the medium.


The yeast extract would consume and metabolize some of the medium components and metabolic products will be formed. This new introduction of products by the yeast, whether waste materials or otherwise, is unaccounted for and changes the composition of the medium. Therefore, it would no longer be chemically defined.


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The number of available media to grow bacteria is considerable. Some media are considered general all-purpose media and support growth of a large variety of organisms. A prime example of an all-purpose medium is tryptic soy broth (TSB). Specialized media are used in the identification of bacteria and are supplemented with dyes, pH indicators, or antibiotics. One type, enriched media, contains growth factors, vitamins, and other essential nutrients to promote the growth of fastidious organisms, organisms that cannot make certain nutrients and require them to be added to the medium. When the complete chemical composition of a medium is known, it is called a chemically defined medium. For example, in EZ medium, all individual chemical components are identified and the exact amounts of each is known. In complex media, which contain extracts and digests of yeasts, meat, or plants, the precise chemical composition of the medium is not known. Amounts of individual components are undetermined and variable. Nutrient broth, tryptic soy broth, and brain heart infusion, are all examples of complex media.

Figure 1. On this MacConkey agar plate, the lactose-fermenter E. coli colonies are bright pink. Serratia marcescens, which does not ferment lactose, forms a cream-colored streak on the tan medium. (credit: American Society for Microbiology)

Media that inhibit the growth of unwanted microorganisms and support the growth of the organism of interest by supplying nutrients and reducing competition are called selective media. An example of a selective medium is MacConkey agar. It contains bile salts and crystal violet, which interfere with the growth of many gram-positive bacteria and favor the growth of gram-negative bacteria, particularly the Enterobacteriaceae. These species are commonly named enterics, reside in the intestine, and are adapted to the presence of bile salts. The enrichment cultures foster the preferential growth of a desired microorganism that represents a fraction of the organisms present in an inoculum. For example, if we want to isolate bacteria that break down crude oil, hydrocarbonoclastic bacteria, sequential subculturing in a medium that supplies carbon only in the form of crude oil will enrich the cultures with oil-eating bacteria. The differential media make it easy to distinguish colonies of different bacteria by a change in the color of the colonies or the color of the medium. Color changes are the result of end products created by interaction of bacterial enzymes with differential substrates in the medium or, in the case of hemolytic reactions, the lysis of red blood cells in the medium. In Figure 1, the differential fermentation of lactose can be observed on MacConkey agar. The lactose fermenters produce acid, which turns the medium and the colonies of strong fermenters hot pink. The medium is supplemented with the pH indicator neutral red, which turns to hot pink at low pH. Selective and differential media can be combined and play an important role in the identification of bacteria by biochemical methods.

Think about It

  • Distinguish complex and chemically defined media.
  • Distinguish selective and enrichment media.

The End-of-Year Picnic

The microbiology department is celebrating the end of the school year in May by holding its traditional picnic on the green. The speeches drag on for a couple of hours, but finally all the faculty and students can dig into the food: chicken salad, tomatoes, onions, salad, and custard pie. By evening, the whole department, except for two vegetarian students who did not eat the chicken salad, is stricken with nausea, vomiting, retching, and abdominal cramping. Several individuals complain of diarrhea. One patient shows signs of shock (low blood pressure). Blood and stool samples are collected from patients, and an analysis of all foods served at the meal is conducted.

Bacteria can cause gastroenteritis (inflammation of the stomach and intestinal tract) either by colonizing and replicating in the host, which is considered an infection, or by secreting toxins, which is considered intoxication. Signs and symptoms of infections are typically delayed, whereas intoxication manifests within hours, as happened after the picnic.

Blood samples from the patients showed no signs of bacterial infection, which further suggests that this was a case of intoxication. Since intoxication is due to secreted toxins, bacteria are not usually detected in blood or stool samples. MacConkey agar and sorbitol-MacConkey agar plates and xylose-lysine-deoxycholate (XLD) plates were inoculated with stool samples and did not reveal any unusually colored colonies, and no black colonies or white colonies were observed on XLD. All lactose fermenters on MacConkey agar also ferment sorbitol. These results ruled out common agents of food-borne illnesses: E. coli, Salmonella spp., and Shigella spp.

Figure 2. Gram-positive cocci in clusters. (credit: Centers for Disease Control and Prevention)

Analysis of the chicken salad revealed an abnormal number of gram-positive cocci arranged in clusters (Figure 2). A culture of the gram-positive cocci releases bubbles when mixed with hydrogen peroxide. The culture turned mannitol salt agar yellow after a 24-hour incubation.

All the tests point to Staphylococcus aureus as the organism that secreted the toxin. Samples from the salad showed the presence of gram-positive cocci bacteria in clusters. The colonies were positive for catalase. The bacteria grew on mannitol salt agar fermenting mannitol, as shown by the change to yellow of the medium. The pH indicator in mannitol salt agar is phenol red, which turns to yellow when the medium is acidified by the products of fermentation.

The toxin secreted by S. aureus is known to cause severe gastroenteritis. The organism was probably introduced into the salad during preparation by the food handler and multiplied while the salad was kept in the warm ambient temperature during the speeches.

  • What are some other factors that might have contributed to rapid growth of S. aureus in the chicken salad?
  • Why would S. aureus not be inhibited by the presence of salt in the chicken salad?

Key Concepts and Summary

  • Chemically defined media contain only chemically known components.
  • Selective media favor the growth of some microorganisms while inhibiting others.
  • Enriched media contain added essential nutrients a specific organism needs to grow
  • Differential media help distinguish bacteria by the color of the colonies or the change in the medium.

Multiple Choice

EMB agar is a medium used in the identification and isolation of pathogenic bacteria. It contains digested meat proteins as a source of organic nutrients. Two indicator dyes, eosin and methylene blue, inhibit the growth of gram-positive bacteria and distinguish between lactose fermenting and nonlactose fermenting organisms. Lactose fermenters form metallic green or deep purple colonies, whereas the nonlactose fermenters form completely colorless colonies. EMB agar is an example of which of the following?

  1. a selective medium only
  2. a differential medium only
  3. a selective medium and a chemically defined medium
  4. a selective medium, a differential medium, and a complex medium

Haemophilus influenzae must be grown on chocolate agar, which is blood agar treated with heat to release growth factors in the medium. H. influenzae is described as ________.

Fill in the Blank

Blood agar contains many unspecified nutrients, supports the growth of a large number of bacteria, and allows differentiation of bacteria according to hemolysis (breakdown of blood). The medium is ________ and ________.

Rogosa agar contains yeast extract. The pH is adjusted to 5.2 and discourages the growth of many microorganisms however, all the colonies look similar. The medium is ________ and ________.

Think about It

What is the major difference between an enrichment culture and a selective culture?

Critical Thinking

Haemophilus, influenzae grows best at 35–37 °C with

5% CO2 (or in a candle-jar) and requires hemin (X factor) and nicotinamide-adenine-dinucleotide (NAD, also known as V factor) for growth. [1] Using the vocabulary learned in this chapter, describe H. influenzae.


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Homework question on chemically defined medium - Biology

Different Types of Cells

There are lots of different types of cells. Each type of cell is different and performs a different function. In the human body, we have nerve cells which can be as long as from our feet to our spinal cord. Nerve cells help to transport messages around the body. We also have billions of tiny little brain cells which help us think and muscle cells which help us move around. There are many more cells in our body that help us to function and stay alive.

Although there are lots of different kinds of cells, they are often divided into two main categories: prokaryotic and eukaryotic.

Prokaryotic Cells - The prokaryotic cell is a simple, small cell with no nucleus. Organisms made from prokaryotic cells are very small, such as bacteria. There are three main regions of the prokaryotic cell:

1) The outside protection or "envelope" of the cell. This is made up of the cell wall, membrane, and capsule.
2) The flagella, which are a whip-like appendages that can help the cell to move. Note: not all prokaryotic cells have flagella.
3) The inside of the cell called the cytoplasmic region. This region includes the nucleoid, cytoplasm, and ribosomes.

Eukaryotic Cells - These cells are typically a lot bigger and more complex than prokaryotic cells. They have a defined cell nucleus which houses the cell's DNA. These are the types of cells we find in plants and animals.


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Accompanies CHEM 3403. Explores the principles covered in CHEM 3403 by laboratory experimentation. Experiments include measurement of reaction kinetics, such as excited state dynamics, measurement of gas transport properties, atomic and molecular absorption and emission spectroscopy, infrared spectroscopy of molecular vibrations, and selected applications of fluorimetry.

Corequisite(s): CHEM 3403

CHEM 3410. Environmental Geochemistry. (4 Hours)

Offers students who wish to work in the geosciences or environmental science and engineering fields, including on the land, in freshwater, or the oceans, an opportunity to understand the geochemical principles that shape the natural and managed environment. Seeks to provide a context for understanding the natural elemental cycles and environmental problems through studies in atmospheric, terrestrial, freshwater, and marine geochemistry. Topics include fundamental geochemical principles environmental mineralogy organic and isotope geochemistry the global carbon, nitrogen, and phosphorous cycles atmospheric pollution environmental photochemistry and human-natural climate change feedbacks. ENVR 3410 and CHEM 3410 are cross-listed.

Attribute(s): NUpath Analyzing/Using Data, NUpath Natural/Designed World

CHEM 3431. Physical Chemistry. (4 Hours)

Offers an in-depth survey of physical chemistry. Emphasizes applications in modern research, including examples from biochemistry. Topics include the laws of thermodynamics and their molecular interpretation equilibrium in chemical and biochemical systems molecular transport kinetics, including complex enzyme mechanisms and an introduction to spectroscopy and the underlying concepts of quantum chemistry.

Prerequisite(s): ((CHEM 1214 with a minimum grade of C- or CHEM 1220 with a minimum grade of C-) or (CHEM 1151 with a minimum grade of C- or CHEM 1161 with a minimum grade of C-)) (MATH 1252 with a minimum grade of C- or MATH 1342 with a minimum grade of C-) (PHYS 1147 with a minimum grade of C- or PHYS 1155 with a minimum grade of C- or PHYS 1165 with a minimum grade of C- or PHYS 1175 with a minimum grade of C-)

Corequisite(s): CHEM 3432

CHEM 3432. Lab for CHEM 3431. (1 Hour)

Accompanies CHEM 3431. Covers practical skills in physical chemistry with an emphasis on current practice in chemistry, biochemistry, and pharmaceutical science. Introduces both ab initio and biological molecular modeling, differential scanning calorimetry, polymer characterization, protein unfolding and protein/ligand binding, electronic absorption spectroscopy, and synthesis of nanoparticles or quantum dots.

Corequisite(s): CHEM 3431

CHEM 3501. Inorganic Chemistry. (4 Hours)

Presents the following topics: basic concepts of molecular topologies, coordination compounds, coordination chemistry, isomerism, electron-transfer reactions, substitution reactions, molecular rearrangements and reactions at ligands, and biochemical applications.

Prerequisite(s): (CHEM 2313 with a minimum grade of C- or CHEM 2317 with a minimum grade of C-) (CHEM 2321 with a minimum grade of C- or CHEM 2331 with a minimum grade of C- or CHEM 3331 with a minimum grade of C-)

Attribute(s): NUpath Writing Intensive

CHEM 3502. Lab for CHEM 3501. (1 Hour)

Offers a laboratory course in inorganic chemistry with experiments and projects that track with the topics discussed in CHEM 3501. Designed to provide laboratory experience with the synthesis of coordination compounds and with the instrumental methods used to characterize them.

CHEM 3503. Recitation for CHEM 3501. (0 Hours)

Offers students additional opportunities to work interactively with instructors and other students to learn and apply the concepts presented in CHEM 3501.

CHEM 3505. Introduction to Bioinorganic Chemistry. (4 Hours)

Explores basic concepts of molecular topologies, coordination compounds, coordination chemistry, isomerism, electron-transfer reactions, substitution reactions, molecular rearrangements, and reactions at ligands in the context of metal-based drugs, imaging agents, and metalloenzymes.

Prerequisite(s): (CHEM 2313 with a minimum grade of C- or CHEM 2317 with a minimum grade of C-) (CHEM 2321 with a minimum grade of C- or CHEM 2331 with a minimum grade of C- or CHEM 3331 with a minimum grade of C-)

Attribute(s): NUpath Writing Intensive

CHEM 3506. Lab for CHEM 3505. (1 Hour)

Offers a laboratory course in inorganic chemistry with experiments and projects that track with the topics discussed in CHEM 3505. Designed for students who have mastered basic laboratory techniques in general and organic chemistry. Introduces new synthetic techniques and applies modern analytical characterization tools not previously used in other laboratory courses (such as CHEM 3522 and CHEM 3532).

CHEM 3507. Recitation for CHEM 3505. (0 Hours)

Offers students additional opportunities to work interactively with instructors and other students to learn and apply the concepts presented in CHEM 3505.

CHEM 3521. Instrumental Methods of Analysis. (1 Hour)

Introduces the instrumental methods of analysis used in all fields of chemistry, with an emphasis on understanding not only the fundamental principles of each method but also the basics of the design and operation of the relevant instrumentation.

Prerequisite(s): CHEM 2331 with a minimum grade of C- or CHEM 3331 with a minimum grade of C-

Corequisite(s): CHEM 3522

CHEM 3522. Instrumental Methods of Analysis Lab. (4 Hours)

Accompanies CHEM 3521. Lab experiments provide hands-on experience in the instrumental methods of analysis discussed in CHEM 3521, such as high-performance liquid chromatography, gas chromatography, mass spectrometry, capillary electrophoresis, atomic absorption, cyclic voltammetry, and UV-vis spectroscopy.

Prerequisite(s): CHEM 2331 with a minimum grade of C- or CHEM 3331 with a minimum grade of C-

Corequisite(s): CHEM 3521

CHEM 3531. Chemical Synthesis Characterization. (1 Hour)

Introduces advanced techniques in chemical synthesis and characterization applicable to organic, inorganic, and organometallic compounds. Techniques used include working under inert atmosphere, working with liquefied gases, and handling moisture-sensitive reagents, NMR, IR, and UV-vis spectroscopy.

Prerequisite(s): CHEM 2317 with a minimum grade of C-

Corequisite(s): CHEM 3532

CHEM 3532. Chemical Synthesis Characterization Lab. (4 Hours)

Acompanies CHEM 3531. Covers topics from the course through various experiments.

Prerequisite(s): (CHEM 2313 with a minimum grade of C- or CHEM 2317 with a minimum grade of C-) (CHEM 2321 with a minimum grade of C- or CHEM 2331 with a minimum grade of C-)

Corequisite(s): CHEM 3531

CHEM 3990. Elective. (1-4 Hours)

Offers elective credit for courses taken at other academic institutions. May be repeated without limit.

CHEM 4456. Organic Chemistry 3: Organic Chemistry of Drug Design and Development. (4 Hours)

Offers students majoring in chemistry an opportunity to apply the principles gained in two semesters of organic chemistry and chemical biology to a relevant disciplinary context. The discovery, design, and development of biologically active compounds for medical purposes uses knowledge and techniques gained in both organic synthesis and chemical biology. It directs those skills to incorporate specific chemical features into organic compounds to meet biological criteria. As such, it seeks to develop problem-solving skills that are valuable across a range of chemical disciplines and not confined to synthetic organic chemistry alone.

Prerequisite(s): CHEM 2317 with a minimum grade of C-

Corequisite(s): CHEM 4457

CHEM 4457. Lab for CHEM 4456. (2 Hours)

Accompanies CHEM 4456. Includes literature research activities, field trips, case studies, and presentations. Offers students an opportunity to prepare for a wider range of career options.

Corequisite(s): CHEM 4456

CHEM 4460. Enzymes: Chemistry and Chemical Biology. (4 Hours)

Focuses on enzymes: their chemistry, mechanisms, and applications. Examines the underlying chemical and mechanistic principles. Introduces the techniques and approaches in enzymology. Bridges the gap between classroom learning and real-world practice in the related fields, e.g., medicinal chemistry, chemical biology, engineering, and pharmaceutical research.

Prerequisite(s): CHEM 2313 with a minimum grade of C-

CHEM 4620. Introduction to Protein Chemistry. (4 Hours)

Introduces protein chemistry in the context of molecular medicine. Discusses analytical methods used to elucidate the origin, structure, function, and purification of proteins. Surveys the synthesis and chemical properties of structurally and functionally diverse proteins, including globular, membrane, and fibrous proteins. Discusses the role of intra- and intermolecular interactions in determining protein conformation, protein folding, and in their enzymatic activity. Intended for undergraduate students without prior experience in protein chemistry.

Prerequisite(s): CHEM 2313 with a minimum grade of C- or CHEM 2317 with a minimum grade of C-

CHEM 4621. Introduction to Chemical Biology. (4 Hours)

Probes the structure and function of biological macromolecules and the chemical reactions carried out in living systems, including biological energetics. Discusses techniques to measure macromolecular interactions and the principles and forces governing such interactions. Offers students an opportunity to gain experience in reading and evaluating primary literature. Intended for undergraduate students with no prior knowledge of the field.

Prerequisite(s): (CHEM 2317 with a minimum grade of C- or CHEM 2313 with a minimum grade of C-) (CHEM 2321 with a minimum grade of C- or CHEM 2331 with a minimum grade of C- or CHEM 3331 with a minimum grade of C-) (CHEM 3401 (may be taken concurrently) with a minimum grade of C- or CHEM 3421 (may be taken concurrently) with a minimum grade of C- or CHEM 3431 (may be taken concurrently) with a minimum grade of C-)

Corequisite(s): CHEM 4622

CHEM 4622. Lab for CHEM 4621. (1 Hour)

Accompanies CHEM 4621. Complements and reinforces the concepts from CHEM 4621 with an emphasis on fundamental techniques. Offers students an opportunity to complete independent projects in modern chemical biology research.

Prerequisite(s): ENGW 1111 with a minimum grade of C or ENGW 1102 with a minimum grade of C or ENGL 1111 with a minimum grade of C or ENGL 1102 with a minimum grade of C

Corequisite(s): CHEM 4621

CHEM 4628. Introduction to Spectroscopy of Organic Compounds. (4 Hours)

Examines the application of modern spectroscopic techniques to the structural elucidation of small organic molecules. Emphasizes the use of H and C NMR spectroscopy supplemented with information from infrared spectroscopy and mass spectrometry. Explores both the practical and nonmathematical theoretical aspects of 1D and 2D NMR experiments. Topics include the chemical shift, coupling constants, the nuclear Overhauser effect and relaxation, and 2D homonuclear and heteronuclear correlation. Designed for chemists who do not have an extensive math or physics background no prior knowledge of NMR spectroscopy is assumed.

Prerequisite(s): CHEM 2313 with a minimum grade of C- or CHEM 2317 with a minimum grade of C-

Corequisite(s): CHEM 4629

CHEM 4629. Identification of Organic Compounds. (2 Hours)

Introduces the use of the nuclear magnetic resonance (NMR) spectrometer and basic NMR experiments. Determines the identity of unknown organic compounds by the use of mass spectrometry, infrared spectroscopy, and 1D and 2D nuclear magnetic resonance spectroscopy.

Prerequisite(s): CHEM 2313 with a minimum grade of C- or CHEM 2317 with a minimum grade of C-

Corequisite(s): CHEM 4628

CHEM 4750. Senior Research. (4 Hours)

Conducts original experimental work under the direction of members of the department on a project. Introduces experimental design based on literature and a variety of techniques depending upon the individual project.

Prerequisite(s): CHEM 2313 with a minimum grade of C- or CHEM 2317 with a minimum grade of C-

Attribute(s): NUpath Capstone Experience, NUpath Writing Intensive

CHEM 4901. Undergraduate Research. (4 Hours)

Conducts original research under the direction of members of the department. May be repeated without limit.

Prerequisite(s): CHEM 2313 with a minimum grade of C- or CHEM 2317 with a minimum grade of C- or CHEM 2321 with a minimum grade of C-

Attribute(s): NUpath Integration Experience

CHEM 4970. Junior/Senior Honors Project 1. (4 Hours)

Focuses on in-depth project in which a student conducts research or produces a product related to the student’s major field. Combined with Junior/Senior Project 2 or college-defined equivalent for 8 credit honors project. May be repeated without limit.

Attribute(s): NUpath Capstone Experience

CHEM 4971. Junior/Senior Honors Project 2. (4 Hours)

Focuses on second semester of in-depth project in which a student conducts research or produces a product related to the student’s major field. May be repeated without limit.

Prerequisite(s): CHEM 4970 with a minimum grade of C

Attribute(s): NUpath Capstone Experience, NUpath Writing Intensive

CHEM 4990. Elective. (1-4 Hours)

Offers elective credit for courses taken at other academic institutions. May be repeated without limit.

CHEM 4991. Research. (4 Hours)

Offers an opportunity to conduct research under faculty supervision. May be repeated without limit.

Attribute(s): NUpath Integration Experience

CHEM 4992. Directed Study. (1-4 Hours)

Offers independent work under the direction of members of the department on a chosen topic. Course content depends on instructor. May be repeated without limit.

CHEM 4993. Independent Study. (1-4 Hours)

Offers independent work under the direction of members of the department on a chosen topic. Course content depends on instructor. May be repeated without limit.

CHEM 4994. Internship. (4 Hours)

Offers students an opportunity for internship work. May be repeated without limit.

Attribute(s): NUpath Integration Experience

CHEM 5179. Complex Fluids and Everyday Materials. (4 Hours)

Introduces intra- and intermolecular forces and moves on to material deformation in response to external stress, including polymeric elasticity. Covers topics in colloidal science and biological physics: the microscopic origins of suspension stability and biological self-assembly. Additional topics include “molecular gastronomy,” personal care and cleaning products, active materials, and experimental techniques. Studies of complex fluids and soft materials are highly interdisciplinary. Many everyday materials are combinations of the three phases of matter—solid, liquid, and gas—with unique material properties. “Complex fluids” and “soft matter” refer to suspensions, emulsions, foams, and gels, which include personal care items, household cleaners, and even food. Nearly all biological material can be described as a soft material.

CHEM 5460. Enzymes: Chemistry and Chemical Biology. (3 Hours)

Focuses on enzymes: their chemistry, mechanisms, and applications. Examines the underlying chemical and mechanistic principles. Introduces the techniques and approaches in enzymology. Bridges the gap between classroom learning and real-world practice in the related fields, e.g., medicinal chemistry, chemical biology, engineering, and pharmaceutical research.

Prerequisite(s): CHEM 2313 with a minimum grade of C- or CHEM 2317 with a minimum grade of C- or graduate program admission

CHEM 5501. Chemical Safety in the Research Laboratory. (1 Hour)

Covers the material needed to complete successfully all the online safety training that is required for our graduate students, best practices for the safe execution of common chemical laboratory procedures, advanced procedures, as well as incidents from the recent literature. Includes discussions of case studies on topics relevant for the safe and effective use of chemicals and other materials in a research laboratory environment. Undergraduates may enroll with permission of the instructor.

CHEM 5550. Introduction to Glycobiology and Glycoprotein Analysis. (3 Hours)

Covers the background and methods used for glycoprotein characterization. Offers students an opportunity to obtain the background needed to assess the analytical steps necessary for development of glycoprotein drugs. Analyzes regulatory issues behind glycoprotein drug development. Covers recent developments in analytical and regulatory sciences.

CHEM 5599. Introduction to Research Skills and Ethics in Chemistry. (0 Hours)

Seeks to prepare students for success in CHEM 5600 and in CHEM 7730. May be repeated once. Must be taken in consecutive semesters before registration into CHEM 5600 and CHEM 7730.

CHEM 5600. Research Skills and Ethics in Chemistry. (3 Hours)

Discusses ethics in science. Topics include documentation of work in your laboratory notebook, safety in a chemistry research laboratory, principles of experimental design, online computer searching to access chemical literature, reading and writing technical journal articles, preparation and delivery of an effective oral presentation, and preparation of a competitive research proposal.

Prerequisite(s): CHEM 5599 with a minimum grade of S

CHEM 5610. Polymer Chemistry. (3 Hours)

Discusses the synthesis and analysis of polymer materials. Covers mechanisms and kinetics of condensation/chain-growth polymerization reactions and strategies leading to well-defined polymer architectures and compositions, including living polymerizations (free radical, cationic, anionic), catalytic approaches, and postpolymerization functionalization. Discusses correlation of chemical composition and structure to physical properties and applications.

Prerequisite(s): ((CHEM 2317 with a minimum grade of C- or CHEM 2313 with a minimum grade of C-) (CHEM 3401 (may be taken concurrently) with a minimum grade of C- or CHEM 3421 (may be taken concurrently) with a minimum grade of C- or CHEM 3431 (may be taken concurrently) with a minimum grade of C-)) or graduate program admission

CHEM 5611. Analytical Separations. (3 Hours)

Describes the theory and practice of separating the components of complex mixtures in the gas and liquid phase. Also includes methods to enhance separation efficiency and detection sensitivity. Covers thin-layer, gas, and high-performance liquid chromatography (HPLC) and recently developed techniques based on HPLC including capillary and membrane-based separation, and capillary electrophoresis.

CHEM 5612. Principles of Mass Spectrometry. (3 Hours)

Describes the theory and practice of ion separation in electrostatic and magnetic fields and their subsequent detection. Topics include basic principles of ion trajectories in electrostatic and magnetic fields, design and operation of inlet systems and electron impact ionization, and mass spectra of organic compounds.

CHEM 5613. Optical Methods of Analysis. (3 Hours)

Describes the application of optical spectroscopy to qualitative and quantitative analysis. Includes the principles and application of emission, absorption, scattering and fluorescence spectroscopies, spectrometer design, elementary optics, and modern detection technologies.

CHEM 5614. Electroanalytical Chemistry. (3 Hours)

Describes the theory of electrode processes and modern electroanalytical experiments. Topics include the nature of the electrode-solution interface (double layer models), mass transfer (diffusion, migration, and convection), types of electrodes, reference electrodes, junction potentials, kinetics of electrode reactions, controlled potential methods (cyclic voltammetry, chronoamperometry), chronocoulometry and square wave voltammetry, and controlled current methods (chronopotentiometry).

CHEM 5616. Protein Mass Spectrometry. (3 Hours)

Offers students an opportunity to obtain a fundamental understanding of modern mass spectrometers, the ability to operate these instruments, and the ability to prepare biological samples. Undoubtedly the most popular analytical method in science, mass spectrometry is utilized in fields ranging from subatomic physics to biology. Focuses on the analysis of proteins, with applications including biomarker discovery, tissue characterization, detection of blood doping, drug discovery, and the characterization of protein-based therapeutics. By the end of the course, the student is expected to be able to solve a particular chemistry- or biology-related problem by choosing the appropriate sample preparation methods and mass spectrometer.

CHEM 5617. Protein Mass Spectrometry Laboratory. (3 Hours)

Offers students an opportunity to develop an appreciation of the appropriate choice of mass spectrometer for a particular application.

CHEM 5618. Advanced Mass Spectrometry. (3 Hours)

Applies earlier study of mass spectrometry (the principles of modern mass spectrometry hardware and spectral interpretation) to experimental design and data analysis of drugs, proteins, and proteomes. Examines how to choose the appropriate mass spectrometry method for a given biological problem find and acquire an exemplar data set and interpret the data as well as expert practitioners do. As one of the most popular analytical methods in science, mass spectrometry is utilized in fields ranging from subatomic physics to biology. Applications have an overarching theme of human health and include biomarker discovery and validation, tissue analysis (including alternatives to histopathology), and drug development.

Prerequisite(s): CHEM 5612 with a minimum grade of C

CHEM 5620. Protein Chemistry. (3 Hours)

Describes proteins (what they are, where they come from, and how they work) in the context of analytical analysis and molecular medicine. Discusses the chemical properties of proteins, protein synthesis, and the genetic origins of globular proteins in solution, membrane proteins, and fibrous proteins. Covers the physical intra- and intermolecular interactions that proteins undergo along with descriptions of protein conformation and methods of structural determination. Explores protein folding as well as protein degradation and enzymatic activity. Highlights protein purification and biophysical characterization in relation to protein analysis, drug design, and optimization.

CHEM 5621. Principles of Chemical Biology for Chemists. (3 Hours)

Explores the use of natural and unnatural small-molecule chemical tools to probe macromolecules, including affinity labeling and click chemistry. Covers nucleic acid sequencing technologies and solid-phase synthesis of nucleic acids and peptides. Discusses in-vitro selection techniques, aptamers, and quantitative issues in library construction. Uses molecular visualization software tools to investigate structures of macromolecules. Intended for graduate and advanced undergraduate students.

Prerequisite(s): ((CHEM 2313 with a minimum grade of C- or CHEM 2317 with a minimum grade of C-) (CHEM 2321 with a minimum grade of C- or CHEM 2331 with a minimum grade of C- or CHEM 3331 with a minimum grade of C-) (CHEM 3401 (may be taken concurrently) with a minimum grade of C- or CHEM 3421 (may be taken concurrently) with a minimum grade of C- or CHEM 3431 (may be taken concurrently) with a minimum grade of C-)) or graduate program admission

CHEM 5622. Lab for CHEM 5621. (1 Hour)

Accompanies CHEM 5621. Complements and reinforces the concepts from CHEM 5621 with emphasis on fundamental techniques. Offers an opportunity to complete independent projects in modern chemical biology research.

Prerequisite(s): ((CHEM 2313 with a minimum grade of C- or CHEM 2317 with a minimum grade of C-) (CHEM 2321 with a minimum grade of C- or CHEM 2331 with a minimum grade of C- or CHEM 3331 with a minimum grade of C-) (CHEM 3401 (may be taken concurrently) with a minimum grade of C- or CHEM 3421 (may be taken concurrently) with a minimum grade of C- or CHEM 3431 (may be taken concurrently) with a minimum grade of C-) (ENGL 1111 with a minimum grade of C or ENGL 1102 with a minimum grade of C or ENGW 1111 with a minimum grade of C or ENGW 1102 with a minimum grade of C)) or graduate program admission

Attribute(s): NUpath Writing Intensive

CHEM 5625. Chemistry and Design of Protein Pharmaceuticals. (3 Hours)

Covers the chemical transformations and protein engineering approaches to protein pharmaceuticals. Describes protein posttranslational modifications, such as oxidation, glycosylation, formation of isoaspartic acid, and disulfide. Then discusses bioconjugate chemistry, including those involved in antibody-drug conjugate and PEGylation. Finally, explores various protein engineering approaches, such as quality by design (QbD), to optimize the stability, immunogenicity, activity, and production of protein pharmaceuticals. Discusses the underlying chemical principles and enzymatic mechanisms as well.

Prerequisite(s): (CHEM 2317 with a minimum grade of C- or CHEM 2313 with a minimum grade of C- or graduate program admission) (CHEM 5620 (may be taken concurrently) with a minimum grade of C- or CHEM 5621 (may be taken concurrently) with a minimum grade of C-

CHEM 5626. Organic Synthesis 1. (3 Hours)

Surveys types of organic reactions including stereochemistry, influence of structure and medium, mechanistic aspects, and synthetic applications.

CHEM 5627. Mechanistic and Physical Organic Chemistry. (3 Hours)

Surveys tools used for elucidating mechanisms including thermodynamics, kinetics, solvent and isotope effects, and structure/reactivity relationships. Topics include molecular orbital theory, aromaticity, and orbital symmetry. Studies reactive intermediates including carbenes, carbonium ions, radicals, biradicals and carbanions, acidity, and photochemistry.

CHEM 5628. Principles of Spectroscopy of Organic Compounds. (3 Hours)

Studies how to determine organic structure based on proton and carbon nuclear magnetic resonance spectra, with additional information from mass and infrared spectra and elemental analysis. Presents descriptive theory of nuclear magnetic resonance experiments and applications of advanced techniques to structure determination. Includes relaxation, nuclear Overhauser effect, polarization transfer, and correlation in various one- and two- dimensional experiments. Requires graduate students to have one year of organic chemistry or equivalent.

Prerequisite(s): CHEM 2313 with a minimum grade of C- or CHEM 2317 with a minimum grade of C- or graduate program admission

CHEM 5629. Advanced Physical Organic Chemistry. (3 Hours)

Studies the importance of molecular orbital theory in stereoelectronic effects, thermal, and photochemical pericyclic reactions. Offers students an opportunity to obtain the reasoning skills to analyze an organic transformation and apply guiding structural and electronic principles to build intuition on the chemo-, stereo-, and regioselectivity of reactions. Some of these concepts include quantum mechanics, molecular orbital theory, structure and bonding, conformational analysis, hybridization, aromaticity, and hyperconjugation. Students engage in peer-review, literature presentations and collaborative problem solving.

CHEM 5630. Nucleic Acid Chemistry. (3 Hours)

Offers a broadband introduction to the field of nucleic acid chemistry. Nucleic acids are vital for biology, but their roles have been greatly expanded beyond storage of genetic information. The breadth of utility of nucleic acids stems from a precise understanding of their structures, modern means to synthesize and modify them, and the ability for nucleic acids to engage with varieties of enzymes/proteins and other synthetic/biological systems. Foundational topics include nucleic acid structure, physicochemical properties, syntheses of nucleosides/nucleotides/oligonucleotides, chemical modification of nucleic acids, methods to manipulate and analyze nucleic acids (e.g., PCR, sequencing, and electrophoresis). Advanced topics include nucleic acid therapeutics (e.g., siRNA, antisense technology, CRISPR, and aptamers) DNA damage and repair and DNA for materials science (e.g., DNA nanotechnology).

CHEM 5636. Statistical Thermodynamics. (3 Hours)

Briefly reviews classical thermodynamics before undertaking detailed coverage of statistical thermodynamics, including probability theory, the Boltzmann distribution, partition functions, ensembles, and statistically derived thermodynamic functions. Reconsiders the basic concepts of statistical thermodynamics from the modern viewpoint of information theory. Presents practical applications of the theory to problems of contemporary interest, including polymers and biopolymers, nanoscale systems, molecular modeling, and bioinformatics.

Prerequisite(s): CHEM 3401 with a minimum grade of C- or CHEM 3421 with a minimum grade of C- or CHEM 3431 with a minimum grade of C- or graduate program admission

CHEM 5638. Molecular Modeling. (3 Hours)

Introduces molecular modeling methods that are basic tools in the study of macromolecules. Is structured partly as a practical laboratory using a popular molecular modeling suite, and also aims to elucidate the underlying physical principles upon which molecular mechanics is based. These principles are presented in supplemental lectures or in laboratory workshops.

CHEM 5640. Biopolymeric Materials. (3 Hours)

Examines the structure, properties, and processing of biomaterials, the forms of matter that are produced by or interact with biological systems. One of the pillars of biomedical engineering is to use naturally derived and synthetic biomaterials to treat, augment, or replace human tissues.

CHEM 5641. Computational Chemistry. (3 Hours)

Introduces basic concepts, methods, techniques, and recent advances in computational chemistry and their relevance to experimental characterizations such as spectroscopy. Topics include electronic structure theory (wave function theory and density functional theory), principles of molecular dynamics simulations, multiscale modeling, machine learning, and quantum computing relevant to computational chemistry. Builds a theoretical foundation for students to properly choose computational methods to solve common research problems in chemistry, biochemistry, and materials science. Also introduces the field of research in computational chemistry. Suitable for advanced undergraduate students and graduate students who plan to conduct research in the field of computational chemistry or plan to utilize computational techniques to complement experimental research in the molecular sciences.

CHEM 5648. Chemical Principles and Application of Drug Metabolism and Pharmacokinetics. (3 Hours)

Offers students an opportunity to obtain a comprehensive grounding in the chemistry of drug metabolism and pharmacokinetics (DMPK) and its application to drug design and optimization. Multiple rounds of chemical synthesis and testing are usually required to discover new drugs with the appropriate balance of properties such as potency and selectivity, efficacy in preclinical models of disease, safety, and pharmacokinetics. Introduces students to modern tools and concepts utilized to screen for favorable DMPK properties, as well as methods to predict human PK from in vitro and preclinical data. Examines the linkage between drug levels in the body, pharmacodynamic response (PK/PD), and drug-drug interactions in the context of the iterative process of chemical drug synthesis.

CHEM 5651. Materials Chemistry of Renewable Energy. (3 Hours)

Studies renewable energy in terms of photovoltaics, photoelectrochemistry, fuel cells, batteries, and capacitors. Focuses on the aspects of each component and their relationships to one another.

Prerequisite(s): ((CHEM 2313 with a minimum grade of C- or CHEM 2317 with a minimum grade of C-) CHEM 3403 with a minimum grade of C-) or graduate program admission

CHEM 5655. Molecular Symmetry and Group Theory. (3 Hours)

Covers symmetry operations point groups and classification of molecules into point groups as well as matrix representation of symmetry operations, orthogonality theorem, and its use in determining irreducible representation spanned by a basis. Studies decomposition of reducible representation and direct products, characters and character tables, and reviews quantum mechanics. Also covers infrared and Raman spectroscopy, normal modes of vibrations, determining symmetry of vibrations, the role of symmetry in selection rules, LCAO MO theory, Hückel method, electronic spectroscopy, and vibronic spectroscopy and symmetry.

CHEM 5660. Analytical Biochemistry. (3 Hours)

Covers the analysis of biological molecules, which include nucleic acids, proteins, carbohydrates, lipids, and metabolites. Discusses isolation, characterization, and quantification of these molecules.

CHEM 5672. Organic Synthesis 2. (3 Hours)

Continues CHEM 5626. Surveys types of organic reactions including stereochemistry, influence of structure and medium, mechanistic aspects, and synthetic applications.

Prerequisite(s): CHEM 5626 with a minimum grade of C-

CHEM 5676. Bioorganic Chemistry. (3 Hours)

Covers host guest complexation by crown ethers, cryptands, podands, spherands, and so forth molecular recognition including self-replication peptide and protein structure coenzymes and metals in bioorganic chemistry nucleic acid structure interaction of DNA with proteins and small molecules including DNA-targeted drug design catalytic RNA and catalytic antibodies.

Prerequisite(s): (CHEM 5626 with a minimum grade of C- CHEM 5627 with a minimum grade of C-) or graduate program admission

CHEM 5688. Principles of Nuclear Magnetic Resonance. (3 Hours)

Presents the physical principles underlying magnetic resonance spectroscopy, including Fourier transform theory, classical and quantum-mechanical treatments of spin angular momentum, the Bloch equations, and spin relaxation. Covers fundamental concepts in time domain magnetic resonance methods, including pulse sequences, selective pulses, phase cycling, coherence pathways, field gradients, and nonuniform sampling. Surveys the NMR methods most commonly applied to chemical structural analysis, including pure shift NMR 2D correlation (COSY, DQF-COSY, TOCSY, HSQC, HMBC) methods and cross-relaxation (NOESY, ROESY) methods.

CHEM 5700. Topics in Organic Chemistry. (3 Hours)

Offers various topics within the breadth of organic chemistry. Intended to meet the needs and interests of students. Topics could range from the physical and material aspects of organic chemistry to the biochemical and biomedical aspects of organic chemistry. Undergraduate students who have completed a second semester of organic chemistry with a grade of at least C– may be admitted with permission of instructor. May be repeated once.

CHEM 5904. Seminar. (1 Hour)

Focuses on oral reports by master of science and PlusOne participants on current research topics in chemistry and chemical biology. May be repeated up to two times.

CHEM 5976. Directed Study. (1-4 Hours)

Offers independent work under the direction of members of the department on a chosen topic. Course content depends on instructor. May be repeated without limit.

CHEM 5984. Research. (1-6 Hours)

Offers an opportunity to conduct research under faculty supervision. May be repeated up to three times for up to 6 total credits.


Homework question on chemically defined medium - Biology

Tag words: bacterial nutrition, bacterial growth, culture medium, selective medium, minimal medium, enrichment medium, synthetic medium, defined medium, complex medium, fastidious organism, aerobe, anaerobe, obligate anaerobe, facultative anaerobe, aerotolerant anaerobe, superoxide dismutase, catalase, psychrophile, thermophile, extreme thermophile, acidophile, alkalophile, osmophile, osmotolerant, water activity.

Culture Media for the Growth of Bacteria

For any bacterium to be propagated for any purpose it is necessary to provide the appropriate biochemical and biophysical environment. The biochemical (nutritional) environment is made available as a culture medium, and depending upon the special needs of particular bacteria (as well as particular investigators) a large variety and types of culture media have been developed with different purposes and uses. Culture media are employed in the isolation and maintenance of pure cultures of bacteria and are also used for identification of bacteria according to their biochemical and physiological properties.

The manner in which bacteria are cultivated, and the purpose of culture media, varies widely. Liquid media are used for growth of pure batch cultures, while solidified media are used widely for the isolation of pure cultures, for estimating viable bacterial populations, and a variety of other purposes. The usual gelling agent for solid or semisolid medium is agar, a hydrocolloid derived from red algae. Agar is used because of its unique physical properties (it melts at 100 o C and remains liquid until cooled to 40 o C, the temperature at which it gels) and because it cannot be metabolized by most bacteria. Hence as a medium component it is relatively inert it simply holds (gels) nutrients that are in aquaeous solution.

Types of Culture Media

Culture media may be classified into several categories depending on their composition or use. A chemically-defined (synthetic) medium (Table 4a and 4b) is one in which the exact chemical composition is known. A complex (undefined) medium (Table 5a and 5b) is one in which the exact chemical constitution of the medium is not known. Defined media are usually composed of pure biochemicals off the shelf complex media usually contain complex materials of biological origin such as blood or milk or yeast extract or beef extract, the exact chemical composition of which is obviously undetermined. A defined medium is a minimal medium (Table 4a) if it provides only the exact nutrients (including any growth factors) needed by the organism for growth. The use of defined minimal media requires the investigator to know the exact nutritional requirements of the organisms in question. Chemically-defined media are of value in studying the minimal nutritional requirements of microorganisms, for enrichment cultures, and for a wide variety of physiological studies. Complex media usually provide the full range of growth factors that may be required by an organism so they may be more handily used to cultivate unknown bacteria or bacteria whose nutritional requirement are complex (i.e., organisms that require a lot of growth factors, known or unknown). Complex media are usually used for cultivation of bacterial pathogens and other fastidious bacteria.


Figure 2. Legionella pneumophila. Direct fluorescent antibody (DFA) stain of a patient respiratory tract specimen. © Gloria J. Delisle and Lewis Tomalty. Queens University, Kingston, Ontario, Canada. Licensed for use by ASM Microbe Library http://www.microbelibrary.org. In spite of its natural occurrence in water cooling towers and air conditioners, Legionella is a fastidious bacterium grown in the laboratory, which led to the long lag in identification of the first outbreak of Legionnaire's disease in Philadelphia in 1977. Had fluorescent antibody to the bacterium been available at that time, diagnosis could have been made as quickly as the time to prepare and view this slide.

Most pathogenic bacteria of animals, which have adapted themselves to growth in animal tissues, require complex media for their growth. Blood, serum and tissue extracts are frequently added to culture media for the cultivation of pathogens. Even so, for a few fastidious pathogens such as Treponema pallidum, the agent of syphilis, and Mycobacterium leprae, the cause of leprosy, artificial culture media and conditions have not been established. This fact thwarts the the ability to do basic research on these pathogens and the diseases that they cause.

Other concepts employed in the construction of culture media are the principles of selection and enrichment. A selective medium is one which has a component(s) added to it which will inhibit or prevent the growth of certain types or species of bacteria and/or promote the growth of desired species. One can also adjust the physical conditions of a culture medium, such as pH and temperature, to render it selective for organisms that are able to grow under these certain conditions.

A culture medium may also be a differential medium if allows the investigator to distinguish between different types of bacteria based on some observable trait in their pattern of growth on the medium. Thus a selective, differential medium for the isolation of Staphylococcus aureus, the most common bacterial pathogen of humans, contains a very high concentration of salt (which the staph will tolerate) that inhibits most other bacteria, mannitol as a source of fermentable sugar, and a pH indicator dye. From clinical specimens, only staph will grow. S. aureus is differentiated from S. epidermidis (a nonpathogenic component of the normal flora) on the basis of its ability to ferment mannitol. Mannitol-fermenting colonies (S. aureus) produce acid which reacts with the indicator dye forming a colored halo around the colonies mannitol non-fermenters (S. epidermidis) use other non-fermentative substrates in the medium for growth and do not form a halo around their colonies.

An enrichment medium employs a slightly different twist. An enrichment medium (Table 5a and 5b) contains some component that permits the growth of specific types or species of bacteria, usually because they alone can utilize the component from their environment. However, an enrichment medium may have selective features. An enrichment medium for nonsymbiotic nitrogen-fixing bacteria omits a source of added nitrogen to the medium. The medium is inoculated with a potential source of these bacteria (e.g. a soil sample) and incubated in the atmosphere wherein the only source of nitrogen available is N2. A selective enrichment medium (Table 5b) for growth of the extreme halophile (Halococcus) contains nearly 25 percent salt [NaCl], which is required by the extreme halophile and which inhibits the growth of all other procaryotes.


Table 4a. Minimal medium for the growth of Bacillus megaterium. An example of a chemically-defined medium for growth of a heterotrophic bacterium.

Component Amount Function of component
sucrose 10.0 g C and energy source
K2HPO4 2.5 g pH buffer P and K source
KH2PO4 2.5 g pH buffer P and K source
(NH4)2HPO4 1.0 g pH buffer N and P source
MgSO4 7H2O 0.20 g S and Mg ++ source
FeSO4 7H2O 0.01 g Fe ++ source
MnSO4 7H2O 0.007 g Mn ++ Source
water 985 ml
pH 7.0



Table 4b. Defined medium (also an enrichment medium) for the growth of Thiobacillus thiooxidans, a lithoautotrophic bacterium.

Component Amount Function of component
NH4Cl 0.52 g N source
KH2PO4 0.28 g P and K source
MgSO4 7H2O 0.25 g S and Mg ++ source
CaCl2 2H2O 0.07 g Ca ++ source
Elemental Sulfur 1.56 g Energy source
CO2 5%* C source
water 1000 ml
pH 3.0
* Aerate medium intermittently with air containing 5% CO2.


Table 5a. Complex medium for the growth of fastidious bacteria.

Component Amount Function of component
Beef extract 1.5 g Source of vitamins and other growth factors
Yeast extract 3.0 g Source of vitamins and other growth factors
Peptone 6.0 g Source of amino acids, N, S, and P
Glucose 1.0 g C and energy source
Agar 15.0 g Inert solidifying agent
water 1000 ml
pH 6.6


Table 5b. Selective enrichment medium for growth of extreme halophiles.


34 Fundamental Q&As on Cell Membrane

A membrane is any delicate sheet that separates one region from another, blocking or permitting (selectively or completely) the passage of substances. The skin, for example, can be considered a membrane that separates the inside and the outside of the body cellophane, used in chemical laboratories to separate solutions, also acts as a membrane.

More Bite-Sized Q&As Below

2. How are membranes classified according to their permeability?

Membranes can be classified as impermeable, permeable, semipermeable or selectively permeable.

An impermeable membrane is one through which no substance can pass. Semipermeable membranes are those which only let solvents, such as water, pass through them. Permeable membranes are those which let solvents and solutes, such as ions and molecules, to pass through them. There are also selectively permeable membranes, which are membranes that, in addition to allowing the passage of solvents, let specific solutes pass through while blocking others.

Diffusion and Osmosis

3. What is diffusion?

Diffusion is the spreading of molecules of a substance from a region where the substance is more concentrated to another region where it is less concentrated. For example, when water is boiled, gaseous water particles tend to uniformly spread in the air via diffusion.

4. What does concentration gradient mean? Is it correct to refer to the “concentration gradient of water”?

The concentration gradient is the difference in the concentration of a substance between two regions.

Concentration is a term used to designate the quantity of a solute divided by the total quantity of a solution. Since water, in general, is the solvent in this situation, it is not correct to refer to the “concentration of water” in a given solution.

5. What is the difference between osmosis and diffusion?

Osmosis is the phenomenon of the movement of solvent particles (in general, water) from a region of lower solute concentration to a region of higher solute concentration. Diffusion, on the other hand, is the movement of solutes from a region of higher solute concentration to a region of lower solute concentration.

Osmosis can be considered the movement of water (solvent) whereas diffusion can be considered the movement of solutes, caused by a concentration gradient.

6. What is osmotic pressure?

In a aqueous solution, osmotic pressure is the pressure that a region of lower solute concentration puts on a region of higher solute concentration, forcing the passage of water from the area of lower solute concentration to the more concentrated region. The intensity of the osmotic pressure (in units of pressure) is equal to the pressure necessary to apply to the solution to prevent its dilution by osmosis.

It is possible to apply pressure to counteract the osmotic pressure on a solution, such as the hydrostatic pressure of the liquid or atmospheric pressure. In plant cells, for example, the rigid cell wall creates pressure that acts against the tendency of water to enter when the cell is in a hypotonic environment. Microscopically, the pressure that counteracts osmotic pressure does not prevent water from passing through a semipermeable membrane, but it does create a water flow in the opposite way as compensation.

7. Can solutions with the same concentration of different solutes have different osmotic pressures?

The osmotic pressure of a solution does not depend on the nature of the solute it only depends on the quantity of molecules (particles) in relation to the total solution volume. Solutions with same concentration of particles, despite containing different solutes, exert the same osmotic pressure.

Even when the solution contains a mixture of different solutes, its osmotic pressure only depends on its total particle concentration, regardless of the nature of the solutes.

8. How are solutions classified according to their comparative tonicity?

When compared to another solution, a solution can be hypotonic (or hyposmotic), isotonic (or isosmotic) or hypertonic (or hyperosmotic).

When a solution is less concentrated than another, it is considered hypotonic compared to that other solution. When it is more concentrated, it is considered hypertonic. When two solutions have the same concentration, ਋oth are designated isotonic. Therefore, this classification makes sense only when comparing solutions.

9. What type of membrane is the cell membrane in terms of permeability?

The cell membrane is a selectively permeable membrane, meaning that it allows the passage of water and some select solutes.

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The Phospholipid Bilayer

10. What are the basic components of the cell membrane?

The cell membrane is formed of lipids, proteins and carbohydrates.

The lipids contained in the membrane are phospholipids, a special type of lipid, which is bound to a phosphate group on one end, thus giving an electrical charge to this region of the molecule. Since phospholipids have one electrically charged end and a long neutral organic chain, they can organize themselves into two layers of attached molecules: the hydrophilic portion (polar) of each layer faces outwards and is in contact with the water (also a polar molecule) located in the extracellular and intracellular space whereas the hydrophobic chains (non-polar) face inwards and are isolated from the water. Because this type of membrane is made of two phospholipid layers, it is also called a bilipid membrane.

Membrane proteins are embedded and dispersed in the compact bilipid structure. Carbohydrates appear in the outer surface of the membrane, attached to some of those proteins in the form of glycoproteins or bound to phospholipids, forming glycolipids. The carbohydrates in the membrane form the glycocalyx of the membrane.

This description of the structure of cell membranes is known as the fluid mosaic model.

11. What are the respective functions of phospholipids, proteins and carbohydrates in the cell membrane?

Phospholipids have a structural function in cell membranes. They form the bilipid membrane that the cell membrane is composed of.

Proteins have several specialized functions in cell membranes. Some of them are channels for substances to pass through the membrane others are receptors and signalers of information others are enzymes others are cell identifiers (cellular markers) and they also participate in the adhesion complexes between cells or between the internal surface of the membrane and the cytoskeleton.

Membrane carbohydrates, attached to proteins or to lipids, are found in the outer surface of the cell membrane. In general, they are used to mark cells so that these cells and their functions are recognized by other cells and substances (for example, they differentiate red blood cells in the ABO blood group system). They also carry out immune modulation functions, pathogen sensitization functions, etc.

Microvilli and Cell Junctions

12. What is differentiation of a cell membrane?

In some types of cells, the cell membrane has different structures that are necessary for the specific functions of the cells. The main ones are the microvilli and the structures for the reinforcement of adhesion between cells (cell junctions).

Microvilli are multiple external projections of the membrane resembling glove fingers. They are found in the cells of tissues in which it is advantageous to increase the size of the surface area in contact with the exterior, for example, in the enteric (intestinal) epithelium for the absorption of nutrients.

Structures that promote the strengthening of the adhesion between cells occur mainly in epithelial tissues where the need for coverage and impermeability requires cells to be “glued” to neighboring cells. These structures can be interdigitations, desmosomes, tight junctions (zonula occludens), zonula adherens (adherens junctions) and gap junctions.

Active and Passive Transport, Simple and Facilitated Diffusion

13. What is the relationship between the concentration gradient and active and passive transport?

Passive transport is the movement of substances across membranes in favor of their concentration gradient, rather, from a more concentrated region to a less concentrated region. Active transport, on the other hand, is the transport of substances across membranes against their concentration gradient, from a less concentrated to a more concentrated region. No energy is used in passive transport because it is spontaneous.ꂬtive transport, on the other hand, requires energy (work) to occur.

Active transport works to maintain or increase the concentration gradient of a substance between two regions while passive transport works to reduce the concentration gradient.

14. What are the three main types of passive transport?

The three main types of passive transport are simple diffusion, osmosis and facilitated diffusion.

Cell Membrane Review - Image Diversity: passive transport

15. What energy source is used in active transport through biological membranes?

The energy necessary for active transport (against the concentration gradient of the transported substance) to occur comes from ATP molecules. Active transport uses chemical energy from ATP.

16. What is the difference between simple and facilitated diffusion? What does the term “facilitated” refer to? 

Simple diffusion is the direct passage of substances across the membrane in favor of their concentration gradient. In facilitated diffusion, the movement of substances is also in favor of their concentration gradient but the substances move bound to specific molecules that act as “permeabilizers”, that is, facilitators of their passage through the membrane.

17. How does the intensity of simple diffusion vary depending on the relation to the concentration gradient of the transported substance?

The higher the concentration gradient of a substance, the more intense its simple diffusion will be. If the concentration gradient diminishes, the intensity of simple diffusion also diminishes.

18. How does the intensity of facilitated diffusion vary depending on the concentration of the transported substance? What is the limiting factor?

Like simple diffusion, facilitated diffusion is more intense when the concentration gradient of the substance is higher and less intense when the gradient is lower. However, in facilitated diffusion, there is a limiting factor: the quantity of the permeases that facilitate transport through the membrane. Even in a situation in which the concentration gradient of the diffusing substance is high, if there are not enough permeases to carry out the transport there will be no increase in the intensity of the diffusion. This situation is called saturation of the transport proteins and it represents the point at which the maximum transport capacity of the substance across the membrane is reached.

19. In a situation in which the transport proteins are not saturated, how can the speed of simple diffusion be compared to the speed of facilitated diffusion?

The action of facilitator proteins in facilitated diffusion makes this type of diffusion faster than simple diffusion (for the same concentration gradient of the transported substance).

20. What does facilitated diffusion have in common with enzymatic chemical reactions?

One of the main examples of facilitated transport is the entrance of glucose from blood into cells. Glucose from blood binds to specific permeases (hexose-transporting permeases) present in the cell membrane and, via diffusion facilitated by these proteins, it enters the cell to carry out its metabolic functions.

Facilitated diffusion resembles chemical catalysis because the transported substances bind to permeases like substrates bind to enzymes and, after one transport job is finished, the permease is not consumed and can transport other molecules.

21. What are some examples of biological activities in which osmosis plays an important role?

Hemolysis (the destruction of red blood cells) by the entrance of water, hydric regulation in plants and the entrance of water into the xylem of vascular plants are all examples of biological phenomena caused by osmosis.

Excessive dilution of blood plasma causes, via osmosis, the entrance of too much water into red blood cells and the subsequent destruction of these cells (hemolysis). Osmosis is also the main process in the maintenance of the flaccid, turgid or plasmolytic states of plant cells. Osmosis is one of the forces responsible for the entrance of water into the roots of plants, since root cells are hypertonic in comparison to the soil.

22. What do facilitated diffusion and active transport have in common? What are the differences between them?

Facilitated diffusion can be confused with active transport because membrane proteins participate in both processes.

However, in active transport the transported substance moves against its concentration gradient, consuming energy. Facilitated diffusion is passive transport in favor of the concentration gradient and does not require energy.

23. Which molecules make active transport through membranes possible?

Active transport is made possible by specific membrane proteins. These proteins are called “pumps” because they “pump” the moving substance through the membrane by using energy from ATP molecules.

The Sodium-Potassium Pump

24. How is the sodium-potassium pump involved in the functions of cell membranes? What is the importance of this protein for cells?

The sodium-potassium pump is the transport protein that maintains the concentration gradient of these ions between the intra and the extracellular spaces. This protein is phosphorylated in each pumping cycle and then pumps three sodium ions outside the cell and two potassium ions inwards. The phosphorylation is caused by the binding of a phosphate donated by one ATP molecule that is then਌onverted into ADP (adenosine diphosphate).

The job of the sodium-potassium pump, also known as sodium-potassium ATPase, is fundamental in the maintaining of the characteristic negative electrical charge on the intracellular side of the membrane of the resting cell and in creating adequate conditions of sodium and potassium concentrations inside and outside the cell to maintain cellular metabolism.

Endocytosis

25. What is mass transport across the cell membrane?

Mass transport is the entrance or exit of substances through the process of being engulfed by portions of membrane. The fusion of internal substance-containing membranous vesicles with the cell membrane is called exocytosis. The entrance of substances into the cell after they have been engulfed by projections of the membrane is called endocytosis.

26. What are the two main types of endocytosis?

Endocytosis is the entrance of material into the cell through being engulfed by portions of the cell membrane.

Endocytosis can be classified as pinocytosis or phagocytosis. In pinocytosis, small particles on the external surface of the membrane stimulate the invagination of the membrane inwards and vesicles full of those particles then detach from the membrane and enter the cytoplasm. In phagocytosis, bigger particles on the external surface of the membrane induce the projection of pseudopods outwards to enclose the particles. The vesicle then detaches from the membrane and enters the cytoplasm, receiving the name phagosome.

Plant Cell Wall

27. How do plant cell walls react when placed in a hypotonic medium?

Plant cell walls (the cover of the cell external to the cell membrane) are made of cellulose, a polymer of glucose.

When a plant cell is placed in a hypotonic medium, it absorbs too much water through osmosis. In that situation, the cell wall pressure acts to counteract the osmotic pressure, thus preventing excessive increases in cellular volume and cell lysis.

28. What is meant by the suction force of a plant cell? Does suction force facilitate or hinder the entrance of water into the cell?

Suction force (SF) is the osmotic pressure of the plant cell vacuole, or rather, the cell sap found inside the vacuole.

Since cell sap is hypertonic in comparison to cytosol, it attracts water, thus increasing the cytosol concentration. Through the osmotic action of the vacuole, the cytosol becomes hypertonic in relation to the exterior and more water enters the cell.

29. What is the turgor pressure of plant cells? Does it make it easier or harder for water to enter plant cells?

Turgor pressure (TP) is the pressure caused by the distension of the plant cell wall against the increase of the cell volume. Turgor pressure works against the entrance of water into the cell, as it forces the exit of water and counteracts the entrance of the solvent via osmosis. 

30. What does the formula DPD = SF – TP mean?

DPD is the abbreviation for diffusion pressure deficit SF (suction force) is vacuolar osmotic pressure and TP is turgor pressure.

The difference between SF and TP determines whether water tends to enter the cell or not. If SF > TP, DPD > 0, water tends to enter the cell by osmosis. If TP > SF, DPD < 0, water cannot enter the cell by osmosis.

31. What are the values of DPD for plant cells in hypertonic, isotonic and hypotonic media?

When plant cells are placed in a hypertonic medium, they will lose water to the exterior, SF > 0 (the vacuolar pressure is high because it is concentrated) and TP = 0 (there is no distension of the cell wall since the cellular volume is reduced), so DPD = SF. These cells are called plasmolysed cells, and they are characterized by the retraction of the cell membrane, which detaches from the cell wall.

When plant cells are placed in a isotonic medium, there is no increase in the internal water volume, SF > 0 and TP = 0 (since the cell wall is not distended). The cell membrane touches the cell wall just slightly,ਊnd the cell is called a flaccid cell.

When plant cells are placed in hypotonic medium, water tends to enter them, SF = TP (since the osmotic pressure is fully compensated by the distension of the cell wall) and DPD = 0. A cell that has expanded to this point is called a turgid cell.

32. What is the formula for the DPD of wilted (shrunken) plant cells? How is this situation possible?

Wilted plant cells are those that have shrunk due to the loss of water by evaporation without enough replacement. In this situation, the cell membrane retracts and detaches from the cell wall.  Moreover, the cell wall expands in length to stimulate the entrance of water, making TP < 0. Since DPD = SF – TP and TP is negative (< 0), its formula becomes DPD = SF + |TP|.

33. What is the deplasmolysis of plant cells?

When placed in a hypertonic medium, plant cells lose a large amount of water and their cell membranes detach from their cell walls. In that situation, the cell is called a plasmolysed cell. When a plasmolysed cell is placed in a hypertonic medium it absorbs water and becomes a turgid cell. This phenomenon is called deplasmolysis.

Dehydration

34. Why are salt and sugar used in the production of dried meats and dried fruits?

Substances that maintain a highly hypertonic environment, such as sugar and salt, are used in the production of dried meats, fruits or fish (for example, cod) because the material to be conserved is dehydrated and the resulting dryness prevents the growth of populations of decomposer organisms (since these organisms also lose water and die).

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IMPLICATIONS FOR UNDERGRADUATE BIOLOGY EDUCATION

Assessment is the process of evaluating evidence of student learning with respect to specific learning goals. Assessment methods have been shown to greatly influence students' study habits (Entwistle and Entwistle, 1992). We agree with other educators who have argued that in the process of constructing a course, assessment is second only to establishing course learning goals for guiding course design (Wiggins and McTighe, 1998 Palomba and Banta, 1999 Pellegrino et al., 2001 Fink, 2003). Though many faculty establish learning goals for their courses, they often struggle with how to evaluate whether their formative and summative assessment methods truly gauge student success in achieving those goals.

Most faculty would agree that we should teach and test students for higher-cognitive skills. However, when faculty are given training in how to use Bloom's and practice ranking their own exam questions, they often realize that the majority of their test questions are at the lower levels of Bloom's. For example, at a national meeting for undergraduate biology education, 97% of the faculty who attended (n = 37) and received a formal lecture on using Bloom's to rank exam questions agreed that only 25% of their exam questions tested for higher-order cognitive skills (unpublished data). Therefore, most of the time we may not be testing or providing students with enough practice at using content and science process skills at higher cognitive levels, even though our goals are that they master the material at all levels. One explanation for this discrepancy may be that biology faculty have not been given the tools and guidelines that would help them to better align their teaching with assessments of student learning. To further emphasize this point, an analysis of exam questions from courses in medical school that should be aimed at developing HOCS (Whitcomb, 2006) are instead predominantly testing at lower cognitive levels (Zheng et al., 2008).

Developing strong assessment methods is a challenging task, and limited resources have been allocated to support faculty in this endeavor. Further, because of the current trend of increasing class size and decreasing teaching assistant support, multiple-choice exams are becoming the most practical assessment method. It is therefore increasingly important for faculty to invest the time necessary to create multiple-choice exam questions that test at the higher levels of Bloom's (Brady, 2005), as well as to develop integrative testing approaches such as requiring students to justify their answers of a small subset of multiple-choice questions (Udovic, 1996 Montepare, 2005). However, in order to accurately gauge student performance, we strongly encourage faculty to include short essay answer questions or other types of questions that test HOCS on their exams. This shift in assessment practice may require additional teaching support from departments and administrations, but we believe this is very important to the cognitive development of our students.

Our aim in developing the BBT was to make an assessment tool for use by biology faculty and students alike. To further facilitate this process, we have created a diverse array of biology-focused examples, inclusive of both specific skills (e.g., graphing) and subdiscipline content (e.g., physiology) that biology students typically encounter. These examples, in conjunction with the BBT, are designed to aid biologists in characterizing questions according to their relative cognitive challenge and, therefore, develop assessment methods that are more closely aligned with an instructor's learning goals. The BBT can also be used in conjunction with BLASt to help students self-diagnose their learning challenges and develop new strategies to strengthen their critical-thinking skills.

Our implementation of the BBT enhanced teaching and learning in a wide variety of instructional environments. Using the BBT, we were able to identify the cognitive levels of learning activities with which students struggle the most and adjust our teaching practices accordingly. The BBT also helped us to create pedagogical transparency and enhance student metacognition. As always, there is a trade-off when class time is used to develop metacognitive skills as opposed to focusing exclusively on course content. However, in our student-based implementation strategies of the BBT, Bloom's Taxonomy was fully integrated into the course subject matter (e.g., designing exam questions at different levels of Bloom's) anecdotal evidence from our students suggests that they continue to use Bloom's to guide their learning strategies in future classes. Given our experience and the well-documented importance of metacognition in student learning in all disciplines, including science (Schraw, 1998 Bransford et al., 2000 Pintrich, 2002 D'Avanzo, 2003 Coutinho, 2007), we consider the potential benefits students may gain from learning Bloom's to far outweigh any consequences of minimally decreasing course content.

We envision that the BBT could help faculty create biology questions at appropriate cognitive levels and in this way provide faculty with a means to (1) assess students' mastery of both biological content and skills and (2) better align their assessments and learning objectives. We believe that use of the BBT by both faculty and students will help students achieve a deeper understanding of the concepts and skills that are required to become successful biologists. On a broader scale, the BBT could aid in development of biology assessment tools that could then be used to examine levels of academic challenge between different types of standardized exams in the life sciences and to facilitate departmental and interinstitutional comparisons of college biology courses.


Watch the video: Introduction to Balancing Chemical Equations (January 2023).