Microbiology with Diseases by Taxonomy 5th Edition By Bauman - Test Bank

Microbiology with Diseases by Taxonomy 5th Edition By Bauman – Test Bank

 

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Microbiology with Diseases by Taxonomy, 5e (Bauman)

Chapter 5   Microbial Metabolism

 

5.1   Multiple Choice Questions

 

1) Which of the following statements concerning cellular metabolism is FALSE?

1. A) Energy obtained from nutrients or light is stored in the bonds of ATP.
2. B) Enzymes are used in both catabolic and anabolic reactions.
3. C) Macromolecules are converted into cell structures via
4. D) The goal of metabolism is reproduction of the organism.
5. E) ATP is used in the formation of macromolecules.

Answer:  C

Bloom’s Taxonomy:  Application

Section:  Basic Chemical Reactions Underlying Metabolism

Learning Outcome:  5.1

 

2) Anabolic reactions may be characterized as

1. A) exergonic.
2. B) breaking large molecules into smaller molecules.
3. C) forming large molecules from smaller molecules.
4. D) producing ATP.
5. E) breaking large molecules into smaller molecules to produce ATP.

Answer:  C

Bloom’s Taxonomy:  Comprehension

Section:  Basic Chemical Reactions Underlying Metabolism

Learning Outcome:  5.1

 

3) Which of the following statements concerning reduction reactions is FALSE?

1. A) An electron acceptor gains an electron.
2. B) They are coupled with oxidation reactions.
3. C) They frequently involve electron carrier molecules.
4. D) An electron acceptor becomes more positively charged.
5. E) A molecule gains a hydrogen atom.

Answer:  D

Bloom’s Taxonomy:  Application

Section:  Basic Chemical Reactions Underlying Metabolism

Learning Outcome:  5.2

 

 

4) The molecule that an enzyme acts upon is known as its

1. A) substrate.
2. B) coenzyme.
3. C) apoenzyme.
4. D) product.
5. E) catalyst.

Answer:  A

Bloom’s Taxonomy:  Knowledge

Section:  Basic Chemical Reactions Underlying Metabolism

Learning Outcome:  5.6

5) Which of the following statements concerning enzymes is FALSE?

1. A) They are usually, but not always, proteins.
2. B) They always function best at 37°C.
3. C) They can be denatured if the pH of their environment is too high or too low.
4. D) They form a temporary intermediate compound with a substrate.
5. E) They can be used to catalyze a chemical reaction over and over again.

Answer:  B

Bloom’s Taxonomy:  Comprehension

Section:  Basic Chemical Reactions Underlying Metabolism

Learning Outcome:  5.7

 

6) Sulfanilamide is an antimicrobial drug that mimics the shape of an important substrate for a particular bacterial enzyme, thereby inhibiting the enzyme. This type of inhibition is known as

1. A) allosteric inhibition.
2. B) competitive inhibition.
3. C) allosteric activation.
4. D) noncompetitive inhibition.
5. E) feedback inhibition.

Answer:  B

Bloom’s Taxonomy:  Knowledge

Section:  Basic Chemical Reactions Underlying Metabolism

Learning Outcome:  5.7

 

7) Which of the following produces NADPH?

1. A) the pentose phosphate pathway only
2. B) the Calvin-Benson cycle only
3. C) the Embden-Meyerhof pathway only
4. D) both the Embden-Meyerhof and Calvin-Benson cycle pathways
5. E) both the pentose phosphate and Entner-Doudoroff pathways

Answer:  E

Bloom’s Taxonomy:  Comprehension

Section:  Carbohydrate Catabolism

Learning Outcome:  5.24

 

 

8) Which of the following statements concerning glycolysis is TRUE?

1. A) It produces ATP by oxidative phosphorylation.
2. B) It occurs in the cell membranes of bacteria.
3. C) It requires the input of ATP and produces ATP.
4. D) It is an alternative to fermentation.
5. E) It involves ribulose 5-phosphate as an intermediate.

Answer:  C

Bloom’s Taxonomy:  Comprehension

Section:  Carbohydrate Catabolism

Learning Outcome:  5.8

9) Many vitamins are important ________ of enzymes.

1. A) protein cofactors
2. B) coenzymes
3. C) allosteric inhibitors
4. D) competitive inhibitors
5. E) activators

Answer:  B

Bloom’s Taxonomy:  Comprehension

Section:  Basic Chemical Reactions Underlying Metabolism

Learning Outcome:  5.6

 

10) Pyruvic acid is a product of

1. A) the Krebs cycle.
2. B) fermentation.
3. C) glycolysis.
4. D) the pentose phosphate pathway.
5. E) both fermentation and the Krebs cycle.

Answer:  C

Bloom’s Taxonomy:  Knowledge

Section:  Carbohydrate Catabolism

Learning Outcome:  5.8

 

11) All of the following are forms of oxidation EXCEPT

1. A) loss of an electron.
2. B) loss of hydrogen atom.
3. C) a dehydrogenation event.
4. D) substrate-level phosphorylation.
5. E) gain of an oxygen atom and its electrons.

Answer:  D

Bloom’s Taxonomy:  Comprehension

Section:  Basic Chemical Reactions Underlying Metabolism

Learning Outcome:  5.2, 5.3

 

 

12) Which of the following can be the final electron acceptor in anaerobic respiration in bacteria?

1. A) nitrate only
2. B) pyruvic acid only
3. C) sulfate only
4. D) both nitrate and sulfate
5. E) nitrate, pyruvic acid, and sulfate

Answer:  D

Bloom’s Taxonomy:  Comprehension

Section:  Carbohydrate Catabolism

Learning Outcome:  5.10, 5.14

13) Which of the following is a non-protein carrier found in some electron transport chains?

1. A) flavoproteins
2. B) metal-containing proteins
3. C) ribozymes
4. D) cytochromes
5. E) ubiquinones

Answer:  E

Bloom’s Taxonomy:  Knowledge

Section:  Carbohydrate Catabolism

Learning Outcome:  5.11

 

14) A phosphate group is transferred from an organic compound to ADP during

1. A) oxidative phosphorylation.
2. B) substrate-level phosphorylation.
3. C) beta-oxidation.
4. D) photophosphorylation.
5. E) anabolic reactions.

Answer:  B

Bloom’s Taxonomy:  Knowledge

Section:  Basic Chemical Reactions Underlying Metabolism

Learning Outcome:  5.3

 

15) Which of the following is a by-product of the catabolism of proteins?

1. A) lactic acid
2. B) acetyl-CoA
3. C) proteases
4. D) ammonia
5. E) carbon dioxide

Answer:  D

Bloom’s Taxonomy:  Comprehension

Section:  Other Catabolic Pathways

Learning Outcome:  5.18

 

 

16) Which of the following is an active enzyme?

1. A) apoenzyme
2. B) cofactor
3. C) coenzyme
4. D) holoenzyme
5. E) subtrate

Answer:  D

Bloom’s Taxonomy:  Comprehension

Section:  Basic Chemical Reactions Underlying Metabolism

Learning Outcome:  5.5

17) Which of the following is/are common to chemiosmosis and the light-dependent reactions of photosynthesis?

1. A) reduction of NADP+ only
2. B) electron transport only
3. C) a proton gradient only
4. D) both electron transport and a proton gradient
5. E) electron transport, a proton gradient, and reduction of NADP+

Answer:  D

Bloom’s Taxonomy:  Application

Section:  Photosynthesis

Learning Outcome:  5.12, 5.23

 

18) Which of the following is a fermentation product useful in the manufacture of cheese?

1. A) acetic acid
2. B) ammonia
3. C) ethanol
4. D) lactic acid
5. E) pyruvic acid

Answer:  D

Bloom’s Taxonomy:  Comprehension

Section:  Carbohydrate Catabolism

Learning Outcome:  5.15

 

19) How many ATP molecules can theoretically be produced from the NADH generated by the catabolism of a molecule of glucose during aerobic respiration?

1. A) 34
2. B) 30
3. C) 38
4. D) 36
5. E) 4

Answer:  B

Bloom’s Taxonomy:  Comprehension

Section:  Carbohydrate Catabolism

Learning Outcome:  5.8

 

 

20) The various types of chlorophyll differ in the

1. A) amount of light they can absorb.
2. B) amount of ATP they produce.
3. C) number of electrons they release.
4. D) amount of oxygen they utilize.
5. E) wavelengths of light they absorb.

Answer:  E

Bloom’s Taxonomy:  Knowledge

Section:  Photosynthesis

Learning Outcome:  5.20

21) Which of the following metabolic processes is commonly used to identify bacteria?

1. A) carbohydrate fermentation
2. B) lipid catabolism
3. C) Krebs cycle products
4. D) lipid synthesis
5. E) pentose phosphate pathway products

Answer:  A

Bloom’s Taxonomy:  Comprehension

Section:  Carbohydrate Catabolism

Learning Outcome:  5.16

 

22) Beta-oxidation of fatty acids produces a substrate of the

1. A) pentose phosphate pathway.
2. B) protein synthesis pathways.
3. C) Embden-Meyerhof pathway.
4. D) Krebs cycle.
5. E) Calvin-Benson cycle.

Answer:  D

Bloom’s Taxonomy:  Comprehension

Section:  Other Catabolic Pathways

Learning Outcome:  5.17

 

23) Which of the following is associated with the Calvin-Benson cycle?

1. A) acetyl-CoA
2. B) TMAO
3. C) RuBP
4. D) FADH2
5. E) PABA

Answer:  C

Bloom’s Taxonomy:  Knowledge

Section:  Photosynthesis

Learning Outcome:  5.24

 

 

24) What is the major product of the Calvin-Benson cycle that can then be used to form glucose?

1. A) CO2
2. B) ATP
3. C) RuBP
4. D) glyceraldehyde 3-phosphate
5. E) NADPH

Answer:  D

Bloom’s Taxonomy:  Comprehension

Section:  Photosynthesis

Learning Outcome:  5.24

25) Chemical reactions that can proceed toward either anabolism or catabolism are called

1. A) glycolytic.
2. B) light-independent.
3. C) synthetic.
4. D) cyclic.
5. E) amphibolic.

Answer:  E

Bloom’s Taxonomy:  Knowledge

Section:  Other Anabolic Pathways

Learning Outcome:  5.25

 

26) If a cell reverses the process of beta-oxidation, which of the following molecules will it make?

1. A) glycerol
2. B) amino acids
3. C) fatty acids
4. D) nucleotides
5. E) starch

Answer:  C

Bloom’s Taxonomy:  Comprehension

Section:  Other Anabolic Pathways

Learning Outcome:  5.27

 

27) When a cell forms an amino acid by adding an amine group derived from ammonia to a precursor metabolite, this process is called

1. A) amination.
2. B) transamination.
3. C) reduction.
4. D) polymerization.
5. E) deamination.

Answer:  A

Bloom’s Taxonomy:  Knowledge

Section:  Other Anabolic Pathways

Learning Outcome:  5.28

 

28) The conversion of amino acids to carbohydrates is an example of

1. A) amination.
2. B) gluconeogenesis.
3. C) substrate-level phosphorylation.
4. D) beta-oxidation.
5. E) electron transport.

Answer:  B

Bloom’s Taxonomy:  Comprehension

Section:  Other Anabolic Pathways

Learning Outcome:  5.26

29) Noncyclic photophosphorylation produces

1. A) ATP only.
2. B) oxygen.
3. C) NADPH only.
4. D) ATP and NADPH.
5. E) water and ATP.

Answer:  D

Bloom’s Taxonomy:  Comprehension

Section:  Photosynthesis

Learning Outcome:  5.22

 

30) The metabolic processes called fermentation

1. A) produce substrates for the Krebs cycle.
2. B) are alternatives for the pentose phosphate pathway.
3. C) use an organic molecule as a final electron acceptor.
4. D) occur only when oxygen is readily available.
5. E) produce substrates for glycolysis.

Answer:  C

Bloom’s Taxonomy:  Comprehension

Section:  Carbohydrate Catabolism

Learning Outcome:  5.14

 

31) Which of the following is TRUE concerning the structure and function of enzymes?

1. A) All enzymes bind cofactors necessary for their function.
2. B) An apoenzyme is a combination of a cofactor bound to a holoenzyme.
3. C) Enzymes can function at a wide range of pH.
4. D) Competitive inhibition of an enzyme occurs when an inhibitor binds to an allosteric site on the enzyme.
5. E) After an enzyme has catalyzed a reaction, it resumes its original shape and can interact with a new substrate molecule.

Answer:  E

Bloom’s Taxonomy:  Application

Section:  Basic Chemical Reactions Underlying Metabolism

Learning Outcome:  5.6

 

 

32) Bacteriochlorophyll a absorbs ________ light.

1. A) 350 nm, ultraviolet
2. B) 425 nm, violet
3. C) 660 nm, red
4. D) both 425 & 660 nm (violet and red)
5. E) all visible

Answer:  A

Bloom’s Taxonomy:  Knowledge

Section:  Photosynthesis

Learning Outcome:  5.20

33) Where is the majority of ATP generated in prokaryotic cells?

1. A) in the cytoplasmic membrane
2. B) in the cytosol
3. C) in the thylakoids
4. D) in the inner mitochondrial membrane
5. E) on ribosomes

Answer:  A

Bloom’s Taxonomy:  Comprehension

Section:  Carbohydrate Catabolism

Learning Outcome:  5.9

 

34) The conversion of pyruvic acid to acetyl-CoA can be described as ________, because a molecule of CO2 is produced as a by-product.

1. A) decarboxylation
2. B) amination
3. C) respiration
4. D) oxidation
5. E) phosphorylation

Answer:  A

Bloom’s Taxonomy:  Knowledge

Section:  Carbohydrate Catabolism

Learning Outcome:  5.9

 

35) Although glycolysis requires an input of ATP, this pathway results in a net gain of two ATP; therefore it is a(n) ________ pathway.

1. A) exergonic
2. B) endergonic
3. C) oxidative
4. D) reductive
5. E) neither exergonic nor endergonic

Answer:  A

Bloom’s Taxonomy:  Application

Section:  Carbohydrate Catabolism

Learning Outcome:  5.1, 5.8

 

 

36) Enzymes known as lyases participate in ________ reactions.

1. A) anabolic
2. B) catabolic
3. C) both anabolic and catabolic
4. D) neither anabolic nor catabolic
5. E) oxidation-reduction

Answer:  B

Bloom’s Taxonomy:  Comprehension

Section:  Basic Chemical Reactions Underlying Metabolism

Learning Outcome:  5.4

37)  The reactions of photosynthesis take place in the ________ of prokaryotes.

1. A) thylakoids
2. B) cytoplasm
3. C) nucleoid
4. D) cristae
5. E) outer membrane

Answer:  A

Bloom’s Taxonomy:  Comprehension

Section:  Photosynthesis

Learning Outcome:  5.20

 

38) During the synthesis of acetyl-CoA from pyruvic acid, ________ is produced.

1. A) ATP
2. B) NADH
3. C) FADH2
4. D) H2O
5. E) acetic acid

Answer:  B

Bloom’s Taxonomy:  Comprehension

Section:  Carbohydrate Catabolism

Learning Outcome:  5.9

 

39) During reactions catalyzed by oxidoreductases an electron donor is

1. A) oxidized.
2. B) reduced.
3. C) synthesized.
4. D) degraded.
5. E) unaltered.

Answer:  A

Bloom’s Taxonomy:  Application

Section:  Basic Chemical Reactions Underlying Metabolism

Learning Outcome:  5.4

 

 

40) Hydrolases are generally involved in ________ reactions.

1. A) anabolic
2. B) catabolic
3. C) both anabolic and catabolic
4. D) neither anabolic nor catabolic
5. E) oxidation-reduction

Answer:  B

Bloom’s Taxonomy:  Comprehension

Section:  Basic Chemical Reactions Underlying Metabolism

Learning Outcome:  5.4

41) Reactions involving ligases are typically ________ reactions.

1. A) anabolic
2. B) catabolic
3. C) both anabolic and catabolic
4. D) neither anabolic nor catabolic
5. E) exergonic

Answer:  A

Bloom’s Taxonomy:  Comprehension

Section:  Basic Chemical Reactions Underlying Metabolism

Learning Outcome:  5.4

 

42) Substrate-level phosphorylation occurs during which of the following stage(s) of glucose catabolism?

1. A) formation of acetyl-CoA
2. B) lysis stage of glycolysis
3. C) energy-conservation stage of glycolysis
4. D) Krebs cycle
5. E) formation of acetyl-CoA and the Krebs cycle

Answer:  C

Bloom’s Taxonomy:  Application

Section:  Carbohydrate Catabolism

Learning Outcome:  5.3, 5.8, 5.9

 

43) The production of NADH takes place during the ________ stage(s) of glycolysis.

1. A) energy-conservation
2. B) energy-investment
3. C) lysis
4. D) lysis and energy-investment
5. E) energy-investment and energy-conservation

Answer:  A

Bloom’s Taxonomy:  Comprehension

Section:  Carbohydrate Catabolism

Learning Outcome:  5.8

 

 

44) Glycolysis begins with a(n) ________ stage(s).

1. A) energy-conservation
2. B) lysis
3. C) energy-investment
4. D) lysis and energy-conservation
5. E) energy-investment and conservation

Answer:  C

Bloom’s Taxonomy:  Comprehension

Section:  Carbohydrate Catabolism

Learning Outcome:  5.8

45)

 

Identify the processes of glucose metabolism represented in Figure 5.1.

1. A) A = electron transport chain, B = Krebs cycle, C = glycolysis, D = fermentation
2. B) A = glycolysis, B = fermentation, C = Krebs cycle, D = electron transport chain
3. C) A = fermentation, B = glycolysis, C = Krebs cycle, D = electron transport chain
4. D) A = glycolysis, B = Krebs cycle, C = fermentation, D = electron transport chain
5. E) A = glycolysis, B = Krebs cycle, C = electron transport chain, D = fermentation

Answer:  B

Bloom’s Taxonomy:  Application

Section:  Carbohydrate Catabolism

Learning Outcome:  5.8

 

46)

 

The process illustrated in the figure above is an example of a(n) ________ reaction.

1. A) amination
2. B) reduction
3. C) oxidation
4. D) transamination
5. E) transferase

Answer:  A

Bloom’s Taxonomy:  Comprehension

Section:  Other Anabolic Pathways

Learning Outcome:  5.28

 

5.2   True/False Questions

 

1) Reactions that are both catabolic and anabolic are amphibolic.

Answer:  TRUE

Bloom’s Taxonomy:  Knowledge

Section:  Other Anabolic Pathways

Learning Outcome:  5.25

 

2) The ability to utilize different metabolites for cellular respiration is one method for identifying bacteria.

Answer:  TRUE

Bloom’s Taxonomy:  Comprehension

Section:  Carbohydrate Catabolism

Learning Outcome:  5.16

 

3) Accumulation of a metabolic pathway product may result in decreased activity of the pathway enzymes.

Answer:  TRUE

Bloom’s Taxonomy:  Comprehension

Section:  Basic Chemical Reactions Underlying Metabolism

Learning Outcome:  5.7

 

 

4) As the concentration of substrate increases, the activity of the enzyme decreases.

Answer:  FALSE

Bloom’s Taxonomy:  Comprehension

Section:  Basic Chemical Reactions Underlying Metabolism

Learning Outcome:  5.7

5) All substrates for ribozymes are RNA molecules.

Answer:  FALSE

Bloom’s Taxonomy:  Comprehension

Section:  Basic Chemical Reactions Underlying Metabolism

Learning Outcome:  5.5

 

6) During chemiosmosis, electrons are pumped across a membrane to produce ATP.

Answer:  FALSE

Bloom’s Taxonomy:  Comprehension

Section:  Carbohydrate Catabolism

Learning Outcome:  5.12

 

7) Some photosynthetic bacteria use chlorophylls other than chlorophyll a.

Answer:  TRUE

Bloom’s Taxonomy:  Comprehension

Section:  Carbohydrate Catabolism

Learning Outcome:  5.20

 

8) All the precursors of amino acids are intermediates of glycolytic and fermentation pathways.

Answer:  FALSE

Bloom’s Taxonomy:  Knowledge

Section:  Other Anabolic Pathways

Learning Outcome:  5.28

 

9) Essential amino acids are amino acids that cannot be synthesized by an organism and so must be provided as nutrients.

Answer:  TRUE

Bloom’s Taxonomy:  Knowledge

Section:  Other Anabolic Pathways

Learning Outcome:  5.28

 

10) The pentose phosphate pathway generates all the necessary precursors for nucleotide biosynthesis.

Answer:  FALSE

Bloom’s Taxonomy:  Knowledge

Section:  Other Anabolic Pathways

Learning Outcome:  5.29

 

 

5.3   Short Answer Questions

 

1) The conversion of phosphoenol pyruvic acid (PEP) to pyruvic acid results in the production of an ATP. This reaction is an example of (substrate-level/oxidative/reductive) phosphorylation.

Answer:  substrate-level

Bloom’s Taxonomy:  Comprehension

Section:  Basic Chemical Reactions Underlying Metabolism

Learning Outcome:  5.3, 5.8

 

2) Another term for a protein catalyst is a(n) (enzyme/ribozyme).

Answer:  enzyme

Bloom’s Taxonomy:  Knowledge

Section:  Basic Chemical Reactions Underlying Metabolism

Learning Outcome:  5.5

3) A(n) (oxidation/reduction/transport) reaction is one in which a molecule accepts an electron.

Answer:  reduction

Bloom’s Taxonomy:  Knowledge

Section:  Basic Chemical Reactions Underlying Metabolism

Learning Outcome:  5.2

 

4) The (activation /inhibition/saturation) point of an enzyme is reached when all active sites have bound substrate molecules.

Answer:  saturation

Bloom’s Taxonomy:  Comprehension

Section:  Basic Chemical Reactions Underlying Metabolism

Learning Outcome:  5.6

 

5) When a noncompetitive inhibitor molecule binds to a(n) (active/allosteric/substrate) site on an enzyme, the shape of the active site changes so that the substrate molecules can no longer bind.

Answer:  allosteric

Bloom’s Taxonomy:  Knowledge

Section:  Basic Chemical Reactions Underlying Metabolism

Learning Outcome:  5.6

 

6) Beta-oxidation of fatty acids produces (acetic acid/acetyl-CoA/glycerol).

Answer:  acetyl-CoA

Bloom’s Taxonomy:  Knowledge

Section:  Other Catabolic Pathways

Learning Outcome:  5.17

 

 

7) Electrons are transferred in the Krebs cycle in the form of (oxygen/hydrogen) atoms to NAD+ and FAD.

Answer:  hydrogen

Bloom’s Taxonomy:  Comprehension

Section:  Carbohydrate Catabolism

Learning Outcome:  5.9

 

8) The purpose of electron transport is to create a proton (concentration/gradient/pump) across a membrane that can then be used to make ATP.

Answer:  gradient

Bloom’s Taxonomy:  Knowledge

Section:  Carbohydrate Catabolism

Learning Outcome:  5.12

 

9) Anaerobic respiration involves the use of molecules other than oxygen as the final electron (acceptor/donor) in an electron transport chain.

Answer:  acceptor

Bloom’s Taxonomy:  Comprehension

Section:  Carbohydrate Catabolism

Learning Outcome:  5.10

10) Laboratory fermentation tests often include a pH indicator because many bacteria produce (O2/bases/acids) as they ferment carbohydrates.

Answer:  acids

Bloom’s Taxonomy:  Comprehension

Section:  Carbohydrate Catabolism

Learning Outcome:  5.15

 

11) Amino acids are converted to substrates of the Krebs cycle by (beta-oxidation/deamination/transamination).

Answer:  deamination

Bloom’s Taxonomy:  Comprehension

Section:  Other Catabolic Pathways

Learning Outcome:  5.18

 

12) Some bacteria use (acetyl-CoA/DHAP/TMAO) as a final electron receptor, resulting in a detectable odor.

Answer:  TMAO

Bloom’s Taxonomy:  Comprehension

Section:  Other Catabolic Pathways

Learning Outcome:  5.18

 

 

13) Anoxygenic photosynthesis typically results in the production of (oxygen/sulfur/ammonia) as a waste product.

Answer:  sulfur

Bloom’s Taxonomy:  Comprehension

Section:  Photosynthesis

Learning Outcome:  5.22

 

14) Cells can use (active/allosteric/substrate) sites to regulate enzyme activity and thereby control their metabolism.

Answer:  allosteric

Bloom’s Taxonomy:  Knowledge

Section:  Integration and Regulation of Metabolic Functions

Learning Outcome:  5.31

 

15) Significant amounts of the NADPH required for the Calvin-Benson cycle are produced during the (cyclic/noncyclic) photophosphorylation reactions of photosynthesis.

Answer:  noncyclic

Bloom’s Taxonomy:  Comprehension

Section:  Photosynthesis

Learning Outcome:  5.22

 

16) Only Photosystem I is required for (anoxygenic/cyclic/noncyclic) photophosphorylation to occur.

Answer:  cyclic

Bloom’s Taxonomy:  Knowledge

Section:  Photosynthesis

Learning Outcome:  5.21, 5.22

 

5.4   Essay Questions

 

1) Describe the mechanism of feedback inhibition and the role this process plays in controlling enzyme activity.

Answer:  Feedback inhibition is also known as negative feedback and end-product inhibition. In this mechanism, the product of a particular metabolic pathway inhibits an enzyme that catalyzes a reaction earlier in the pathway. For example, the end-product might be an allosteric inhibitor of that enzyme, binding to a location on the enzyme outside the active site. When the allosteric inhibitor binds, it changes the shape of the enzyme and prevents the enzyme from binding to its substrate. This “shuts off” the enzyme, and because the product of one reaction is the substrate for another, it shuts down the pathway. The inhibition is released as the amount of the end-product decreases. When this occurs, the pathway will be turned on again, because the cell again needs the end-product. Feedback inhibition controls enzyme activity so that energy and metabolites are not wasted.

Bloom’s Taxonomy:  Application

Section:  Basic Chemical Reactions Underlying Metabolism

Learning Outcome:  5.7

 

2) The discussion of carbohydrate catabolism includes some of the many metabolic variations microbes are capable of. Devise a set of biochemical tests to identify the Gram-negative bacteria mentioned. Assume you can detect various organic compounds. Prepare a dichotomous key of your identification scheme.

Answer:  Many answers are possible. Figure 5.3 shown below is one example, based on glucose and lactose fermentation. Test for ability to ferment glucose and lactose. If glucose is fermented, test for the presence of 6-phosphogluconic acid and 2,3-butandiol.

 

Bloom’s Taxonomy:  Synthesis

Section:  Carbohydrate Catabolism

Learning Outcome:  5.15, 5.16

 

3) Explain why the ATP yield from processes such as cellular respiration is generally given as a theoretical number.

Answer:  The maximum yield of ATP from a single molecule of glucose is 38 ATP molecules. However, any given glucose molecule may produce fewer than this number of ATP molecules for a variety of reasons. A eukaryotic cell spends 2 ATP molecules in transporting NADH produced during glycolysis into the mitochondrion; this reduces the theoretical yield to 36 ATP. The yield might be even lower, because in chemiosmosis there is no direct relationship between the number of electrons used to create a proton gradient and the number of ATP molecules produced from that proton gradient. Proton gradients are used to drive other processes and activities in the cell besides ATP production, so some of the energy that is represented by the proton gradient can be “siphoned off” before it is used to make ATP. Some of the intermediates of glycolysis and the Krebs cycle can be used as substrates for other metabolic processes, and when the intermediates are diverted, the theoretical ATP yield is not realized.

Bloom’s Taxonomy:  Analysis

Section:  Carbohydrate Catabolism

Learning Outcome:  5.8

 

4) Compare and contrast cyclic and noncyclic photophosphorylation.

Answer:  Both cyclic photophosphorylation and noncyclic photophosphorylation are aspects of the light-dependent reactions of photosynthesis. They both involve the excitation of electrons by light energy; these excited electrons then participate in an electron transport pathway to create a proton gradient that can be used to produce ATP through chemiosmosis. However, as its name implies, cyclic photophosphorylation occurs when electrons return to the chlorophyll molecules whence they came. Excited electrons in noncyclic photophosphorylation are also used in the same way to produce ATP; however, these electrons are donated to an NADP+ molecule at the end of their transport chain, producing NADPH as a product of the system. Because electrons are constantly leaving the chlorophyll molecules where they are being excited, and not returning, there must also be a steady source of electrons for the photosystem. These electrons can come from molecules such as water or hydrogen sulfide.

Bloom’s Taxonomy:  Analysis

Section:  Photosynthesis

Learning Outcome:  5.22

 

5) Discuss the interrelationships between anabolic and catabolic pathways. Provide specific examples in your answer.

Answer:  Catabolic pathways generate the energy required for anabolic reactions. Catabolic pathways produce intermediates for other pathways, and some intermediates and products of anabolic pathways provide intermediates for catabolic pathways. The Krebs cycle produces energy to drive amino acid synthesis, and several Krebs cycle intermediates are substrates for amino acid biosynthesis. For example, oxaloacetic acid is a precursor for half a dozen amino acids, and α-ketoglutaric acid is a precursor for about four additional amino acids. The pentose phosphate pathway produces the five-carbon sugar required for nucleotide synthesis, and various amino acids are metabolized to produce the nitrogenous bases in nucleotides. The Krebs cycle produces intermediates and substrates for lipid biosynthesis. Catabolism of amino acids produces a variety of molecules that are intermediates of glycolysis and the Krebs cycle, and the same is true of lipid catabolism.

Bloom’s Taxonomy:  Analysis

Section:  Integration and Regulation of Metabolic Functions

Learning Outcome:  5.30