MCP - Cross - 2/10 - Citric Acid Cycle

Question 1

A membrane transport system is present in the inner mitochondrial membrane to transport which of the following molecules?
A. Pyruvate B. O2
C. NADH D. CO2
E. Dinitrophenol

Answer 1

A. Pyruvate

Remember O2 can diffuse across the membrane

Question 2

The reaction catalyzed by aconitase can be characterized as a(n):
A. oxidative transfer
B. condensation/hydrolysis
C. oxidative decarboxylation
D. substrate-level phosphorylation
E. dehydration/hydration

Answer 2

E. Dehydration/hydration

Question 3

Which of the following enzymes catalyzed a reaction sequence that illustrates the Common Intermediate Principle?
A. Adenylate kinase
B. Hexokinase
C. Fumarase
D. Succinyl-CoA synthetase
E. None of the above

Answer 3

D. Succinyl-CoA synthetase

Question 4

Which of the following is not a function of the CAC?

1. Converts a number of different fuels to a common mobile fuel (NADH).
2. Breaks down glucose to pyruvate conserving the energy available as ATP and NADH
3. Serves as a final meeting place of nearly all oxidizable substrates.
4. Provides intermediates for biosynthesis.

Answer 4

2. is not a function of the CAC.

Question 5

Why are mitochondria often located near structures requiring ATP?

Answer 5

Because this decreases the diffusion path from where ATP is made to where it is needed

Question 6

Where does the citric acid cycle occur?

Answer 6

In the matrix of the mitochondria

Question 7

Name reaction type and enzyme involved in the following:

Acetyl Coa + Oxaloacetate –> Citryl CoA –> Citrate + CoA

Answer 7

Reaction: Condensation and hydrolysis of the thioester

Enzyme: Citrate synthase

Question 8

Name reaction type and enzyme involved in the following:

Citrate –> Cis Aconitase –> Isocitrate

Answer 8

Reaction: Dehydration and hydration

Enzyme: Aconitase

Question 9

Name reaction type and enzyme involved in the following:

Isocitrate –> Oxalosuccinate –> alpha-ketoglutarate

Answer 9

Reaction: Oxidative decarboxylation

Enzyme: Isocitrate dehydrogenase

Question 10

Name reaction type and enzyme involved in the following:

alpha-ketoglutaric acid –> Succinyl CoA

Answer 10

Reaction: Oxidative decarboxylation & formation of thioester

Enzyme: alpha-ketoglutarate dehydrogenase complex

Question 11

Name reaction type and enzyme involved in the following:

Succinyl CoA –> Succinate + CoA

Answer 11

Reaction: Thioester cleavage w/ GTP synthesis

Enzyme: Succinyl CoA synthetase

Question 12

Name reaction type and enzyme involved in the following:

Succinate –> Fumarate –> Malate –> Oxaloacetate

Answer 12

Reaction: Oxidation, hydration, oxidation (respectively)

Enzyme: Succinate dehydrogenase, fumarase, malate dehydrogenase

Question 13

__1__ molecules of GTP are formed from 2 molecules of __2__

Answer 13

1. Two

2. Succinyl CoA

Question 14

Six __1__ are formed in the oxidation of 2 molecules each of __2__, __3__ and __4__

Answer 14

1. NADH
2. isocitrate
3. alpha-ketoglutarate
4. malate

Question 15

__1__ FADH2 are formed in the oxidation of 2 molecules of __2__

Answer 15

1. Two

2. succinate

Question 16

How many ATP/glucose does the citric acid cycle yield?

Answer 16

2 (in the form of GTP)

Question 17

Beriberi syndrome, a deficiency of vitamin B1, results in build-up of what substrate?

Answer 17

Pyruvate
Note than thiamine, aka TPP is vitamin B1, the prosthetic group for condensation and decarboxylation of pyruvate dehydrogenase (E1).

Question 18

Which tissue of the eye relies solely on anaerobic metabolism instead of the CAC/ETC?

Answer 18

The cornea, because access to O2 would compromise the transmission of light

Question 19

Which one of the following is a property of pyruvate dehydrogenase?
A. The enzyme contains only one polypeptide chain
B. The enzyme requires thiamine pyrophosphate as a cofactor.
C. The enzyme produces oxaloacetate from pyruvate.
D. The enzyme is converted to an active form by phosphorylation.

Answer 19

B. The enzyme requires thiamine pyrophosphate as a cofactor.
Pyruvate dehydrogenase converts pyruvate to acetyl-CoA, and contains multiple subunits. Thiamine pyrophosphate, lipoic acid, coA and NAD+ are all cofactors for these reactions.

Question 20

Consider the section of the CAC in which isocitrate is converted to fumarate. This segment can best be described by:
A. These reactions yield 5 moles of high-E phosphate bonds per mole of isocitrate
B. These reactions require a coenzyme synthesized in the human from niacin
C. These reactions are catalyzed by enzymes located solely in the mitochondrial membrane.

Answer 20

B, because NADH contains niacin. Note that isocitrate to fumarate contains 4 steps of the CAC.