MIC205B Exam 2 key

November 1, 2007

Instructor: Dr. Stephen Billington

 

                                                        Name:_______________________________________

 

                                                Student ID:_______________________________________

 

Answers to each question are shown in blue

 

Please make sure that you have entered your name and Student ID at the top of the page.

 

Part 1 MULTIPLE CHOICE: Read each question and the answers carefully. Circle the correct answer on the test paper. Each correct answer is worth 3 points, for a Part 1 total of 45 points.

 

JUSTIFICATIONS: If you are unsure of an answer, you may write a short explanation next to the question on the test paper (this may earn you points if your answer is wrong, but you can justify it).

 

1.   Which of the following does NOT pertain to the TCA cycle?

 

a. Ends with the regeneration of oxaloacetate

 

b. Reduces pyruvate to lactic acid

 

c. Generates NADH₂ and FADH

 

d. Does not participate in fermentation

 

2.   The pathway by which glucose is split and oxidized to two molecules of pyruvate is called

 

a. glycolysis

 

b. fermentation

 

c. the TCA cycle

 

d. the electron transport system

 

3.   During aerobic respiration

 

a. oxygen acts as a source of electrons

 

b. nitrate acts as the terminal electron acceptor

 

c. glucose is oxidized to CO₂ and H₂O

 

d. the TCA cycle is only partially functional

 

4.   What is the primary purpose of the non-glycolytic reactions during fermentation?

 

a. To generate ATP

 

b. To make alcoholic beverages

 

c. To oxidize pyruvate

 

d. To regenerate NAD⁺

 

5.   The following represents what type of reaction?

 

 

 

 

 

 

 

 

 

a. decarboxylation

 

b. redox

 

c. substrate level phosphorylation

 

d. isomerization

 

6.   The term photolithoautotroph refers to microbes which use

 

a. light for energy, organic molecules for carbon and inorganic molecules for electrons

 

b. light for energy, CO₂ for carbon and inorganic molecules for electrons

 

c. organic molecules as carbon, energy and electron sources

 

d. inorganic molecules for energy and electrons, and CO₂ for carbon

 

7.   During photosynthesis the light reactions produce

 

a. glucose

 

b. CO₂ and O₂

 

c. ATP and NADPH₂

 

d. ATP and NADH₂

 

8.   The process of fermentation

 

a. allows independence from O₂

 

b. prevents organisms growing as fast as they would using aerobic respiration

 

c. is very efficient at extracting energy from molecules

 

d. generates NADH₂, FADH and ATP

 

9.   The pathway by which CO₂ is fixed into organic compounds in autotrophic microbes is known as

 

a. deamination

 

b. the Calvin-Benson cycle

 

c. the TCA cycle

 

d. glycolysis

 

10. During anaerobic respiration the terminal electron acceptor is

 

a. chlorophyll

 

b. a derivative of pyruvate

 

c. oxygen

 

d. an inorganic molecule other than oxygen

 

11. Each NADH₂ that enters the electron transport system generates

 

a. 2 ATP

 

b. 3 ATP

 

c. 36 ATP

 

d. 38 ATP

 

12. Reactions in which electrons are transferred from one molecule to another are called

 

a. decarboxylation reactions

 

b. substrate level phosphorylations

 

c. redox reactions

 

d. endogonic reactions

 

13. Triglycerides must be split into glycerol and fatty acids by what type of extracellular enzyme prior to transport into bacterial cells?

 

a. proteases

 

b. amylases

 

c. cellulases

 

d. lipases

 

14. Most microorganisms assimilate nitrogen in the form of

 

a. NH₄⁺

 

b. N₂O

 

c. CO₂

 

d. N₂

 

15. The glyoxylate pathway

 

a. is an alternative to glycolysis

 

b. allows the synthesis of glucose in the absence of a carbohydrate source

 

c. assimilates nitrogen

 

d. replenishes intermediates in the TCA cycle

 

 

Part 2 SHORT ANSWER: Read each question carefully and answer each question in the space provided. Each correct answer is worth 5 points, for a Part 2 total of 45 points.

 

JUSTIFICATIONS: Again, if you are unsure of an answer, you may write a short explanation next to the question on the test paper.

 

16. Alanine can be converted to pyruvate by transamination. What pathway would be used to make glucose if alanine was the sole carbon source?

 

_gluconeogenesis______________

 

17. a.   Which molecule generates more ATP by oxidative phosphorylation when used as a terminal electron acceptor, nitrate or oxygen?

 

__oxygen________________________________

 

 

b. Why?

 

There is a greater reduction potential difference between NADH₂ and oxygen than

 

there is between NADH₂ and nitrate

 

________________________________________________________________

 

 

18. In the following reaction what molecules are represented by the numbers 1, 2 and 3?

 

1. α-ketoglutarate_______

 

2. NADH₂_____________

 

3. CO₂________________

 

 

 

 

19. The disaccharide lactose is split into glucose and galactose by the enzyme β‑galactosidase

 

      a.   How many ATPs can be generated from the complete oxidation of one molecule of lactose by aerobic respiration?

 

___76___ ATPs

 

      b.   How many ATPs would be generated if lactose was fermented to lactic acid and formic acid?

 

____4____ ATPs

 

20. Microbes can breakdown triglycerides into glycerol and fatty acids

 

      a.   How many ATPs will be generated by the aerobic degradation of three fatty acid molecules each with 20 carbons?

 

3 x [(20/2 x17)-1] =507 ATPs

 

      b.   What pathway is used in the catabolism of fatty acids?

 

___β-oxidation______

 

21. Fill in the blanks. In the electron transport system, redox reactions are coupled with the transport of protons across the plasma membrane to generate the proton motive force. Diffusion of protons back across the membrane through ATP synthase results in the synthesis of ATP.

 

22. Draw and name the missing structure in this transamination reaction.

 

 

 

 

 

 

 

 

 

23. a.   True OR False? No ATP is generated by oxidative phosphorylation from NADH₂ produced during glycolysis

 

__FALSE_________

 

      b.   True OR False? The ATP used during the preparatory phase of glycolysis cancels out any ATP generated by substrate level phosphorylation during the energy conserving phase

 

__FALSE_________

 

24. Fill in the blanks. The metabolic intermediates 3-phosphoglyceric acid, diphosphoglyceric acid, and glyceraldehyde-3-phosphate are found in three major metabolic pathways; a pathway for the catabolism of glucose, glycolysis, a pathway for the anabolism of glucose in heterotrophic bacteria, gluconeogenesis and a pathway for the anabolism of glucose in photosynthetic bacteria, Calvin-Benson cycle.

 

 

 

 

 

 

 

 

 

 

 

 

Part 3 SHORT ESSAY: Answer any TWO of the following questions in the space provided. Each correct answer is worth ten points, for a total of 20 points for Part 3.

 

25. Explain the difference between cyclic and non-cyclic photophosphorylation. Why are both mechanisms of photophosphorylation used during photosynthesis?

 

 

In cyclic photophosphorylation, electrons released from P700 in photosystem I, following the absorption of light energy, are transferred through an electron transport system with the synthesis of ATP by chemiosmosis, and return to P700.

 

In non-cyclic photophosphorylation, electrons are released from chlorophyll P700 as before, but are transferred to NADP⁺ to yield NADPH₂. The electrons do not return to P700. Light energy is also absorbed by chlorophyll P680 in photosystem II, electrons are released and transferred through an electron transport system (with ATP synthesis) and make there way to P700, which is returned to its reduced form. Reduced P680 is regenerated by taking electrons fro H₂O with the release of O₂.

 

Two products of photophosphorylation are required for the dark reactions of photosynthesis, NADPH₂ and ATP. 12 NADPH₂ and 18 ATP are required to make one molecule of glucose. Non-cyclic photophosphorylation makes NADPH₂ and ATP in equal amounts. Cyclic photophosphorylation allows the synthesis of additional ATP, with less light energy than non-cyclic photophosphorylation.

 

 

 

 

 

 

 

 

26.       Explain why the direct transfer of electrons from NADH₂ to O₂ is not beneficial to the cell, and how the electron transport system solves this problem.

 

If electrons are passed directly from NADH₂ to O₂ the release of energy will be so large, because of the large reduction potential difference, that the cell will be unable to capture it for use.

 

The electron transport system takes the electrons from NADH₂ and passes them down a chain of electron carriers such that the change in reduction potential is small between any two carriers. This allows the release of smaller packets of energy which can be coupled with the generation of the proton motive force and ATP production

 

 

 

 

 

 

 

 

 

 

27. Explain the relationship between ΔG, K_eq, exergonic and endergonic reactions

 

 

In exergonic reactions;

 

Keq = [products]    >1

          [reactants]

 

Therefore, ΔG is negative, the reaction proceeds as written spontaneously and releases energy

 

In endergonic reactions;

 

Keq = [products]    <1

          [reactants]

 

Therefore, ΔG is positive, the reaction cannot proceed as spontaneously and requires energy input to proceed