Chapter 6. Microbial Metabolism: Fueling Cell Growth Assignment

Consider the picture representing metabolism in E. coli growing in a medium that contains only glucose and a few inorganic salts. The four outputs to the sides represent different anabolic pathways involved in the biosynthesis of the four types of biological macromolecules. These four biological macromolecules are ____, ______, ______, and _______.

- lipids - carbohydrates - proteins - nucleic acids

Each type of the major electron carriers is referred to by two different abbreviations (NAD + / NADH, NADP+ / NADPH, and FAD / FADH2). The first of each pair refers to the _______ form and the second of each pair refers to the ______ form.

- oxidized - reduced

In oxidation-reduction reactions, or redox reactions, the substance that loses electrons is _______, and the substance that gains those electrons is ________

- oxidized - reduced

Which of the following correctly describe cytochromes found in an electron transport chain?

- several different cytochromes exist - cytochromes are proteins that contain heme, a molecule that holds an iron atom in its center

Which of the following are true statements about what happens to glucose inside a cell?

- some glucose might enter glycolysis, only to be siphoned off as a precursor metabolite for biosynthesis - glucose can be used in catabolism to yield energy, or the precursor metabolites generated from its breakdown can be used in anabolism - some glucose might be oxidized to CO2, generating the maximum amount of ATP

Which of the following explain why a cell might undergo fermentation?

- the cell has a limited number of electron carrier molecules that must be regenerated for glycolysis to continue - the cell might lack the pathways for respiration, so fermentation might be the only option - the cell might not have the appropriate terminal electron acceptor available for respiration

Examine the illustration of the electron transport chain and proton motive force in mitochondria. Identify and match each component with the number shown on the figure.

1 = Complex I 2 = Complex II 3 = Complex III 4 = Complex IV

The figure shows three examples of chemoorganotrophic metabolism, with glucose serving as the energy source, and either pyruvate, NO3-, or O2 serving as the terminal electron acceptor. Which of these three possibilities will yield the most energy for the organism?

- Glucose as the energy source and O2 as the terminal electron acceptor

In an electron transport chain, electron carriers are found in what two general locations?

- Grouped into large protein complexes that function as proton pumps - Freely moving in the membrane where they can shuttle electrons between protein complexes

Which of the following describe enzyme specificity?

- Hydrogen and ionic bonding occur to induce the correct fit between substrate and active site - The substrate must align spatially with the active site - With few exceptions, a unique enzyme is required to catalyze each reaction in a cell.

Which of the following describes some of the forms energy represented in this photograph?

- Kinetic energy of the photos that make up sunlight - Potential energy of the water behind the dam - Electrical energy generated by the hydroelectric dam as it captures the energy from moving water

Match the organism(s) with the correct fermentation pathway.

- Lactic acid fermentation = Steptococcus, Lactobacillus - Ethanol fermentation = Saccharomyces - Butyric acid fermentation = Clostridium - Propionic acid fermentation = Propionibacterium - Mixed acids fermentation = E. coli - 2,3-Butanediol fermentation = Enterobacter

The form of energy that results from the electrochemical gradient established by the electron transport chain is the _____.

- Proton motive force

Consider three major groups of electron carriers found in electron transport chains. Match each description with the correct name.

- Quinones = Lipid-soluble organic molecules that move freely in the membrane; include one the serves as a source of vit. K for humans and other mammals - Cytochromes = Proteins that contain heme, a molecule that holds an iron atom in its center. - Flavoproteins = Proteins that are synthesized from the vit. Riboflavin.

In contrast to an exergonic reaction, which of the following accurately describes an endergonic reaction?

- The products have more free energy than the starting compounds. - The reaction requires an input of energy in order to proceed.

In contrast to an endergonic reaction, which of the following accurately describe an exergonic reaction?

- The reaction releases energy as it proceeds - The starting compound have more free energy than the products

For each six-carbon molecule of glucose that enters glycolysis, how many molecules of pyruvate are made, and how many carbon atoms does each pyruvate have?

- Two molecules of pyruvate, each with three carbon atoms

E. coli will preferentially use _____ respiration in the presence of O2, but when O2 is not available, it can switch to ______ respiration if a suitable electron acceptor such as nitrate is present.

- aerobic - anaerobic

A general group of electron carriers found in electron transport chains is quinones, that

- are lipid-soluble organic molecules that move freely in the membrane, transferring electrons between different protein complexes - exist as several types, including ubiquinone and menaquinone

Pyruvate and pyruvic acid _____.

- are terms often used interchangeably by biologists - are terms that refer to the ionized and the undissociated forms of the molecule

In the figure, Compound C electrons to Compound Y. Therefore, Compound X is the electron _______ and Compound Y is the electron _______.

- donor - acceptor

Consider how cells obtain energy to make ATP. The chemical that serves as the electron donor is the _______ source, and the one that ultimately accepts those electrons is the _____ electron acceptor.

- energy - terminal

Sulfa drugs interfere with the bacterial pathway for the synthesis of folate because they _____.

- have a structure similar to intermediate (para-aminobenzoic acid, or PABA) in the pathway - inhibit an enzyme in the pathway

Rank the following energy-generating processes from greatest energy yield at top to least energy yield at the bottom

1. aerobic respiration 2. anaerobic respiration 3. fermentation

For each glucose molecule degraded, the net yield of glycolysis is ______.

2 ATP, 2 NADH, and 6 precursor metabolites

The _____ energy is the energy it takes to start a reaction

Activation

When discussing electron carriers in the context of biological reactions why do we often ignore the location of protons?

In aqueous solutions, protons do not require carriers

Which of the following are important electron carriers for a cell?

NAD+/NADH FAD/FADH2 NADP+/NADPH

Certain intermediates of catabolic pathways, called precursor metabolites, are important because _____.

They serve as carbon skeletons from which subunits of macromolecules can be made.

True or false: because oxidative phosphorylation has so many variables, it is difficult to calculate an accurate ATP yield.

True

Cells can quickly alter the activity of certain key enzymes, using other molecules that bind reversibly and distort them. The control of enzymes is called _______ regulation.

allosteric

The process that links the electron transport chain to ATP synthesis is called the ________ theory.

chemiosmotic

Notice how similar PABA and sulfanilamide are in structure. PABA is a substrate in a pathway leading to folate synthesis. Sulfanilamide is an important inhibitor of the enzyme. What type of inhibitor is sulfanilamide most likely to be?

competitive inhibitor

In prokaryotic cells, all the central metabolic pathways occur in the _____.

cytoplasm

The statement "the substrate fits into the active site of an enzyme like a hand into a glove" refers to what important property of enzymes?

enzyme specificity

The TCA cycle completes the _____ of glucose

oxidation

Proteins are hydrolyzed by proteases, enzymes that break the _____ bonds between amino acid subunits.

peptide

Unlike chemoorganotrophs, photosynthetic organisms generate ATP by ____

photophosphorylation

The step that links glycolysis to the TCA cycle is called the ____ step

transition

The metabolic pathway that oxidizes a 2-carbon acetyl group to release two molecules of CO2 and generates the most reducing power of all the central metabolic pathways is called the ______ acid cycle

tricarboxylic

All of the following accurately describe enzymes EXCEPT _________.

enzymes provide energy to help reactions proceed more rapidly.

Unlike organisms that use organic molecules to fill both their energy and carbon needs, chemolithotrophs must use a process called carbon _____ to produce organic compounds to fulfill their carbon needs.

fixation

Escherichia coli and Pseudomonas aeruginosa both have an electron transport chain that uses O2 as a terminal electron acceptor, yet E. coli is oxidase negative. Based on this information, it is logical to assume that E. coli ______.

lack cytochrome c

______ organisms harvest the energy of sunlight, using it to power the synthesis of organic compounds from CO2, whereas _______ obtain energy by degrading organic compounds made by others.

- photosynthetic - chemoorganotrophs

In prokaryotes, the electron transport chain is located in the _______ membrane, when in the eukaryotic cells it is in the _______ membrane of the mitochondria

- plasma - inner

Energy is the potential to do work and can exist as ____ energy (stored energy) and ____ energy (energy of motion)

- potential - kinetic

Unlike the electrons carried by NADPH, the electrons carried by NADH and FADH2 are _______

- used to produce ATP by oxidative phosphorylation - transferred to the electron transport chain - used to generate proton motive force

Consider the figure showing the formation and breakdown of ATP. Fill in the labels of the figure by matching the terms with their correct number.

1. ATP 2. Energy released drives anabolic reactions 3. ADP 4. Energy used comes from catabolic reactions

Glucose catabolism encompasses two key processes: (1) oxidizing glucose molecules to generate ATP, reducing power, and the precursor metabolites; and (2) transferring the electrons carried by NADH and FADH2 to the terminal electron acceptor. The second process, transfer of electrons, is accomplished by which of the following?

- Cellular respiration - Fermentation

Oxidative phosphorylation and photophosphorylation are similar in that both processes _________.

use an electron transport chain to set up a proton motive force used to generate ATP.

In addition to glucose, which of the following organic compounds can serve as energy sources for microbes?

- Disaccharides - Polysaccharides - Lipids - Fatty Acids - Monosaccharides - Proteins

Comparing the two drawings showing an interaction between a substrate and an enzyme, identify the substrate, the enzyme-substrate complex, the enzyme, and the active site of the enzyme.

1. enzyme 2. substrate 3. active site 4. enzyme-substrate complex

When a single molecule of glucose is processed by glycolysis in an E. coli cell, which of the following make up the net gain of this process?

2 molecules of ATP six precursor metabolites 2 molecules of NADH

Consider the maximum theoretical ATP yield from oxidative phosphorylation of a single molecule of glucose in prokaryotes. Match the relative contributions of the central metabolic pathways and final yield with their approximate contribution in terms of ATP. Include the following pair, already given: G ATP from the transition step.

6 ATP: Glycolysis 22 ATP: TCA cycle 34 ATP: Total maximum yield

The main energy currency of cells is ______

ATP

Consider the ATP-generating process of prokaryotic Chemoorganoheterotrophs. Match the process with its correct terminal electron acceptor.

Aerobic respiration = O2 Anaerobic respiration = Molecule other than O2 such as nitrate, nitrite, or sulfate Fermentation = Organic molecule (pyruvate or a derivative)

Glycolysis can be viewed as having two phases. Why is the initial phase referred to as the investment phase or preparatory phase?

Energy is spent to add two high-energy phosphate groups to glucose, which is then split to yield two 3-carbon molecules

How does a non-competitive inhibitor work on an enzyme?

It binds to a site other than the active site, altering the shape of the enzyme so the substrate can no longer bind

Most chemoorganotrophs, like the one shown in the figure, depend on the metabolic activities of photosynthesis organisms. Consider the forms of energy represented in the figure, and match each type of energy with the correct description.

Kinetic energy = Photons of sunlight Chemical energy = Organic compounds

An atom that has a lower affinity (attraction) for electrons than another is described as _____ than the other

Less electronegative

Other than generating some ATP via the substrate-level phosphorylation steps of glycolysis, what critical role do the additional steps of fermentation accomplish?

They consume excess reducing power in order to regenerate NAD+ so that it can accept electrons to keep glycolysis going.

You are studying bacteria you isolated from sediments at the bottom of a pond. Your research reveals they are using sulfate (SO4 ^2-) as a terminal electron acceptor. This tells you they are capable of _______ respiration.

anaerobic

Prokaryotes that extract electrons from inorganic energy sources and pass them to an electron transport chain to generate a proton motive force that is used to make ATP are called _____.

chemolithotrophs

Identify each of the following by the most precise descriptive term as either a cofactor or coenzyme: NAD+: _____ FAD: _______; copper: _______; coenzyme a: ________.

coenzyme, coenzyme, cofactor, coenzyme

An atom that has a greater affinity (attraction) for electrons than another is described as more ____ than the other.

electronegative

Proteins that function as a biological catalysts are called

enzymes

The central metabolic pathway that splits glucose and gradually oxidizes it to form two molecules of pyruvate is ___________

glycolysis

The series of sequential chemical reactions in a cell that converts a starting compound to an end product is called a ______ pathway

metabolic

Consider the graph of enzyme activity (y-axis) versus pH (x-axis). The point indicated by the question mark is the _______ ________ (middle semi-flat curve)

optimum pH

Consider the graph of enzyme activity (y-axis) versus temperature (x-axis). The point indicated by the question mark is the ___________ _____________. (sharper curve)

optimum temperature

The central metabolic pathway that breaks down glucose but whose primary role is the production of compounds used in biosynthesis, including reducing power in the form of NADPH as well as two precursor metabolites, is called the _______ _____ pathway

pentose phosphate

Match up the correct descriptions with the numbers shown in the drawing to complete the visual analogy of electrons flowing through an electron transport chain.

- 1. - Electrons from the energy source - 2. - Energy released is used to generate a proton motive force - 3. - Electrons donated to the terminal electron acceptor - 4. - High energy - 5. - Low energy

Which of the three central metabolic pathways generate a modest amount of ATP via substrate-level phosphorylation?

-Glycolysis -Tricarboxylic acid (TCA) cycle

Consider the three central metabolic pathways that gradually oxidize glucose to CO2. Why are these amphibolic pathways?

-amphi means both kinds, which reflects the dual role of these central metabolic pathways -although they are catabolic, the precursor metabolites and reducing power they generate can be diverted for biosynthesis (anabolism)

Sulfa drugs inhibit an enzyme in the pathway bacteria use to synthesize folate, making them an effective antimicrobial medication. Why are these medications generally safe for humans?

Human cannot synthesize folate

When an inhibitor binds to a site other than the active site of an enzyme, thereby interfering with its activity this is called ______ inhibition

allosteric

A genus of bacteria that uses fermentation to produce propionic acid and used as part of Swiss cheese production is ________

Propionibacterium

True or false: the change in free energy for a given reaction is the same regardless of the number of steps involved.

True

In a biosynthetic pathway, feedback inhibition refers to _____.

The end product acting as an allosteric inhibitor of the pathway

Place the following steps in the correct order to show how the spatial arrangement of electron carriers in a bacterial electron transport chain helps explain how protons are shuttled from one side of the membrane to the other.

- 1 An electron carrier donates electrons to a hydrogen carrier - 2 the hydrogen carrier passes electrons to a carrier that only accepts electrons - 3 Because the electron carrier only accepts electrons, the protons, are released to the outside of the cell - 4 A proton motive force is setup as protons are moved from the inside of the cell to the outside

Oxidative phosphorylation, the mechanism by which cellular respiration uses the NADH and FADH2 generated in glycolysis, the transition step, and the TCA cycle to synthesize ATP, involves what two steps?

- ATP synthase uses the energy of the proton motive force to drive the synthesis of ATP. - The electron transport chain generates a proton motive force.

Consider the theoretical maximum ATP yield from the complete oxidation of glucose via aerobic respiration in prokaryotes. Match the relative contribution in terms of ATP (substrate-level phosphorylation plus oxidative phosphorylation) with the correct metabolic component.

8 ATP: Glycolysis 6 ATP: Transition step 24 ATP: TCA Cycle 38 ATP: Total yield of aerobic respiration

What is the active site of an enzyme?

The critical site to which a substrate binds by weak forces.

In the representation of an electron transport chain (shown), the terminal electron acceptor is _______

oxygen

Free energy is best defined as _____.

The energy available to do work

Recall that E. coli can grow in glucose-salts medium, which contains only glucose and a few inorganic salts. This means the glucose is serving that two purposes in the cell?

- Energy source - Starting point from which all cell components are made

Match up each type of enzyme inhibition with its characteristic.

Competitive inhibition = Inhibitor binds to the active site of the enzyme, blocking access to the substrate Non-competitive inhibition by regulatory molecules = inhibitor reversibly changes the shape of the enzyme so that the substrate can no longer bind to the active site Non-competitive inhibition by enzyme poisons = Inhibitor binds to the active site of the enzyme, blocking access of the substrate

Match each of the three central metabolic pathways with the correct description.

Glycolysis = Splits glucose and gradually oxidizes it to two molecules of pyruvate; generates some ATP and reducing power plus six precursor. Pentose phosphate pathway = Breaks down glucose, although primary role is production of NADPH and two precursor metabolites for use in biosynthesis Tricarboxylic acid cycle (TCA cycle) = Oxidizes an acetyl group to release two molecules of CO2; generates some ATP and precursor molecules and the most reducing power of all the central metabolic pathways.

Chemolithotrophs fall into four general groups. Match each group below with the appropriate source of energy.

H2 gas = Hydrogen bacteria H2S = Sulfur bacteria Fe2+ = Iron bacteria NH3, HNO2 = Nitrifying bacteria

Match the fermentation pathway with the correct end product(s)

Lactic acid fermentation = Lactic acid Ethanol fermentation = Ethanol, CO2 Butyric acid fermentation = Butyric acid, butanol, acetone, isopropanol, CO2, H2 Propionic acid fermentation = Propionic acid, acetic acid, CO2 Mixed acids fermentation = Acetic acid, lactic acid, succinic acid, ethanol, CO2, H2 2,3-Butanediol fermantation = Formic acid, ethanol, lactic acid, 2,3-butanediol, CO2, H2

Match the term on the left with the description on the right

Metabolism - The sum total of chemical reactions in a cell Catabolism - The set of chemical reactions that degrade compounds, releasing their energy Anabolism - The set of chemical reactions that synthesize and assemble the subunits of macromolecules

Match the following three phosphorylation processes for ATP production with the correct description

Substrate-level phosphorylation = Energy released in an exergonic reaction is used to power the addition of Pi to ADP Oxidative phosphorylation = Energy from exergonic reactions is used to create a proton motive force that drives the addition of Pi to ADP. Photophosphorylation = The sun's radiant energy and an electron transport chain create a proton motive force that drive the addition of Pi to ADP.

Proton motive force is _______.

The form of energy that results from the electrochemical gradient established by the electron transport chain.

Glycolysis can be viewed as having two phases. Why is the second phase referred to as the pay-off phase?

The initial investment of two high-energy phosphate bonds is recovered, and net energy yielded.

When a molecule other than O2 serves as the terminal electron acceptor for the electron transport chain, the organism is utilizing _____ respiration

anaerobic

Consider the effect of temperature on enzyme activity. If the temperature is too high, proteins will ___ and no longer function

denature

Match the type of enzyme inhibition on the left with the example of inhibitor on the right

- Competitive inhibition = Sulfa drugs - Non- competitive inhibition by regulatory molecules = Allosteric regulators - Non-competitive inhibition by enzyme poisons = Mercury

What components are necessary for an electron transport chain?

- Electron carriers such as quinones, cytochromes, and flavoproteins - A membrane - Protein complexes that serve as proton pumps

Lactic acid production by fermenting microorganisms has many benefits for humans, but also can cause some problems. Which of the following are examples of these advantages and disadvantages?

- Results in food spoilage - Production of pickles and cured sausage - Contributes to tooth decay - Creating flavor and texture of yogurt and certain cheeses

Which of the following correctly describe the transition step and the tricarboxylic acid (TCA) cycle?

- Together they generate the most reducing power of all the central metabolic pathways. - They produce three metabolities and ATP - The transition step converts the pyruvate from glycolysis into acetyl-CoA - The TCA cycle oxidizes a 2-carbon acetyle group to release two molecules of CO2.

You are growing E. coli in a medium that includes nitrate. If the bacteria run out of O2, you might expect them to continue growing using _____ respiration, using ______ as a terminal electron acceptor

- anaerobic - nitrate

The three central metabolic pathways that gradually oxide glucose to CO2 are ______, the _____ ____ pathway, and the ______ cycle

- glycolysis - pentose phosphate pathway - the TCA cycle

Which of the following correctly describes respiration?

-Electrons extracted from glucose are transferred to the electron transport chain -The electron transport chain uses the electrons to generation a proton motive force that can be used to generate ATP

In prokaryotes, how does the energy yield of aerobic respiration compare to anaerobic respiration?

The energy yield of aerobic respiration is greater than anaerobic respiration

Which of the following best describes the conversion of energy from one form to another illustrated in the picture?

The potential energy of water stored behind the dam is converted to kinetic energy of moving water, which is converted to electrical current.