Chapter 6: Microbial Metabolism: Fueling Cell Growth

Microorganisms can grow on a variety of organic compounds other than glucose, including polysaccharides, proteins, and lipids. How do they accomplish this?

They break these macromolecules down into appropriate precursor metabolites that are then introduced into central metabolism or used in biosynthesis.

In photosynthesis, what do the light reactions, or light-dependent reactions, accomplish?

They capture radiant energy and convert it to chemical energy in the form of ATP.

In the case of plants, algae, and cyanobacteria, the two major products of photosynthesis are ______.

glucose and oxygen

Starch and cellulose are both polymers made up of the monosaccharide __________, which means that hydrolysis of the polymers releases subunits that can enter directly into the central metabolic pathway of __________ to be oxidized.

glucose, glycolysis

Fats, the most common simple lipids, are broken down by lipases into their component ______. Multiple choice question.

glycerol and fatty acids

Although the pentose phosphate pathway is used by cells to break down glucose, it is particularly important because of its contribution to ____________.

biosynthesis

With respect to their synthesis, how are amino acids typically grouped? a. By how many carbon atoms they contain b. Alphabetically c. By structurally related families that share common biosynthesis pathways d. By their size and molecular weight

c. By structurally related families that share common biosynthesis pathways

Enzymes are biological ______ that are typically _______.

catalysts, protein

Some enzymes act with the assistance of a non-protein component. This component is called a ____________ ; if that component is an organic molecule it can be called a _____________ .

cofactor, coenzymes

Inhibitor binds to the active site of the enzyme, blocking access of the substrate

competitive inhibition

Purines and pyrimidines are synthesized ______. a. by the same pathway b. in successive order, one being made from the other c. one by branched pathway, the other a cyclical pathway d. in distinctly different manners

d. in distinctly different manners

Hydrogen sulfide is produced as a result of certain types of anaerobic respiration. Some chemolithotrophs can then use this as a/an ______.

energy source

All of the following accurately describe enzymes EXCEPT ______.

enzymes provide energy to help reactions proceed more rapidly

Microorganisms that can grow on polysaccharides and disaccharides first break these down to glucose or precursor metabolites that can then enter into the pathway of ____________ to be oxidized.

glycolysis

The primary pathway used by many organisms to convert glucose to pyruvate is ___________.

glycolysis

In terms of their metabolism, prokaryotes are _______ with respect to compounds they use for energy and _______ in their biosynthetic processes.

highly diverse; remarkably similar

The Calvin cycle ______.

incorporates carbon dioxide into organic compounds

The reactions that capture radiant energy and convert it into chemical energy in the form of ATP are called the ________________ reactions.

light-dependent

The TCA cycle completes the _________ of glucose.

oxidation

The mechanism by which cellular respiration uses reducing power generated in glycolysis, the transition step, and the TCA cycle to synthesize ATP is ____________ phosphorylation.

oxidative

The central metabolic pathway that generates reducing power in the form of NADPH is the _____________________ pathway.

pentose phosphate

Energy is the ability to do work and can exist as___________ energy (stored energy) and___________ energy (energy of motion).

potential, kinetic

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

metabolic

The enzymes of the tricarboxylic acid cycle are found in the _____________ matrix in eukaryotes and in the _____________ in prokaryotes.

mitochondrial, cytoplasm

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

peptide or covalent

After a deamination reaction removes the amino group from amino acids, the remaining carbon skeletons are converted into the appropriate ____________ metabolites for entry into central metabolic pathways.

precursor

Identify each of the following by the most precise descriptive term as either a cofactor or coenzyme: magnesium:_________; NADP+: __________; zinc: ____________

magnesium = cofactors NADP+ = coenzymes zinc = cofactors

Autotrophs use carbon dioxide (CO2) to synthesize organic compounds. Which of the following descriptions of this process are true? - It is called carbon fixation. - Plants accomplish it by reversing the steps of the TCA cycle. - In photosynthetic organisms, the process is called the light-independent reactions. - It often involves the Calvin cycle.

- It is called carbon fixation. - In photosynthetic organisms, the process is called the light-independent reactions. - It often involves the Calvin cycle.

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. - Some glucose might be oxidized to CO2, generating the maximum amount of ATP. - All the glucose molecules are oxidized to CO2, generating ATP and reducing power in the process. - 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 enter glycolysis, only to be siphoned off as a precursor metabolite for biosynthesis. - Some glucose might be oxidized to CO2, generating the maximum amount of ATP. - Glucose can be used in catabolism to yield energy, or the precursor metabolites generated from its breakdown can be used in anabolism.

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?

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

The figure illustrates a type of regulation used by cells to rapidly control certain key enzymes. The arrow labeled "1" points to the ___________ site, and the arrow labeled "2" points to the __________ site.

1. allosteric 2. active

Proteins are composed of various combinations of usually how many different amino acids?

20

If the theoretical maximum ATP yield in prokaryotes from oxidative phosphorylation is 34 ATP for a single glucose molecule, what is the total ATP gain when substrate-level phosphorylation is included?

38 ATP

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 = ______________ 6 ATP = ______________ 24 ATP = ______________ 38 ATP = ______________

8 ATP = Glycolysis 6 ATP = Transition step 24 ATP = TCA cycle 38 ATP = Total yield of aerobic respiration

Consider the three key central metabolic pathways (glycolysis, pentose phosphate pathway, and the TCA cycle). What three beneficial products of these pathways?

ATP, reducing power, precursor metabolites

When a cell processes glucose or other organic molecules through its central metabolic pathways, it does so to generate what three critical things?

ATP, reducing power, precursor metabolites

True or false: The Calvin cycle is a two-step linear pathway that photosynthetic organisms use to fix carbon dioxide

False

Considering the general equation that describes photosynthesis, the rate of the process would be most influenced by the availability of _______ in the atmosphere.

CO2

Until the optimal temperature is reached, raising the temperature has what effect on the speed of enzymatic reactions?

It increases their rate.

What happens to an organism if it lacks one or more enzymes in a given biosynthetic pathway?

It must have the end product provided from an external source.

In respiring bacteria, how does ATP synthase generate ATP?

It uses the energy released from allowing protons to flow back into the cell to add a phosphate group to ADP.

The electron transport chain is a cluster of membrane-embedded electron carriers that accept electrons from the coenzymes ________ and _______ and then pass these electrons along the chain.

NADH and FADH2

Which of the following combinations of molecules is produced during the light-dependent reactions of photosynthesis and used in the light-independent reactions?

NADPH and ATP

Inhibitor permanently changes the shape of the enzyme, making the enzyme non-functional

Non-competitive inhibition by enzyme poisons

Inhibitor reversibly changes the shape of the enzyme so that the substrate can no longer bind to the active site

Non-competitive inhibition by regulatory molecules

Some members of which of the following groups can use inorganic chemicals such as hydrogen sulfide and ammonia for energy? - Eukaryotes and prokaryotes - Prokaryotes only - Eukaryotes only

Prokaryotes only

What is the active site of an enzyme?

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

Fats are hydrolyzed by lipases. The glycerol component is then converted to a precursor metabolite, and the fatty acids are degraded using a series of reactions called β-oxidation that remove successive 2-carbon units. Where do these components enter the central metabolic pathways for further oxidation?

The precursor metabolites from glycerol enter glycolysis; the 2-carbon units from fatty acids are added to coenzyme A and enter the TCA cycle.

Although the actual procedure is much more involved, the basic metabolism of wine-making involves inoculating grape juice with a special strain of the yeast Saccharomyces cerevisiae. S. cerevisiae will preferentially perform aerobic respiration on sugars in the juice but can also ferment those sugars to yield CO2 and alcohol, an important component of wine. Assume you inoculate a completely full container of juice and then close the lid. What will the yeast do?

They will grow aerobically, consume the O2 dissolved in the juice, and then switch to fermenting sugars to yield alcohol.

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.

The critical site of an enzyme to which a substrate binds by weak forces is called the___________ .

active site

The light-independent reactions of photosynthesis occur _______ the light-dependent reactions, and function to _______.

after; synthesize organic compounds from CO2

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

allosteric regulation

Nucleotide subunits of DNA and RNA are composed of three units: a 5-carbon sugar, a phosphate group, and a nucleobase. They are initially synthesized ______.

as ribonucleotides that can be converted to deoxyribonucleotides by replacing the 2' hydroxyl group with a hydrogen atom

As part of cellular respiration, a membrane-bound enzyme called ATP ______________ uses energy from a proton-motive force to add a phosphate group to ADP.

synthase

This picture of a set of stairs best exemplifies the electron ___________________ .

transport chain

Which of the following are reasons an organism might use fermentation? select all that apply. a. The energy yield is greater from fermentation than from respiration. b. They lack an electron transport chain. c. A suitable inorganic terminal electron acceptor is not available. D. They lack the ability to perform glycolysis.

b and c

In order to form lipids, how are fatty acids and glycerol synthesized? a. Fatty acid chains come from a precursor near the end of the TCA cycle; glycerol is provided by the pentose phosphate pathway. b. Fatty acid chains are assembled from 2-carbon acetyl groups from the transition step; the precursor to glycerol comes from glycolysis. c. Fatty acid chains are assembled by linking glucose molecules; glycerol comes from the TCA cycle. d. Fatty acid chains are taken from the electron transport chain of respiration; the precursor to glycerol comes from the TCA cycle.

b. Fatty acid chains are assembled from 2-carbon acetyl groups from the transition step; the precursor to glycerol comes from glycolysis.

The process by which chemolithoautotrophs and photoautotrophs incorporate CO2 into organic compounds is called ______________.

carbon fixation

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

denature

Lipid synthesis generally requires the components _________ and __________ acids.

glycerol and fatty acids

In addition to yielding energy, catabolic pathways generate carbon intermediates that can be used in anabolic pathways for the biosynthesis of macromolecules. These carbon skeletons are called ________________________

precursor metabolites

In addition to glucose, which of the following organic compounds can serve as energy sources for microbes? proteins fatty acids polysaccharides monosaccharides disaccharides phosphate lipids

proteins fatty acids polysaccharides monosaccharides disaccharides lipids