Question 1

Which of the following best explains why the citrate cycle is considered the hub of metabolism?

Accepted Answer

It connects carbohydrate, fat, and protein metabolism, provides intermediates for biosynthetic pathways, and regenerates electron carriers for oxidative phosphorylation.

Question 2

During one turn of the citrate cycle, which of the following is produced?

Accepted Answer

3 NADH, 1 FADH2, 2 CO2, 1 GTP

Question 3

Which vitamin is required for the decarboxylation step in the pyruvate dehydrogenase (PDH) reaction?

Accepted Answer

Thiamine

Question 4

A patient presents with symptoms of pellagra. Which biochemical process is most directly affected, and why?

Accepted Answer

Pyruvate dehydrogenase reaction, due to deficiency in niacin affecting NAD+ production.

Question 5

Arsenic poisoning inhibits the pyruvate dehydrogenase complex by binding to which component?

Accepted Answer

The lipoamide group of the E2 enzyme

Question 6

Which step in the citrate cycle is endergonic?

Accepted Answer

Conversion of citrate to isocitrate by aconitase

Question 7

Which equation correctly represents the net reaction of the citrate cycle?

Accepted Answer

$$\mathrm{Acetyl{-}CoA} + 3\ NAD^+ + FAD + GDP + P_i + 2\ H_2O \rightarrow 2\ CO_2$ + 3\ NADH + $$FADH_2$$ + GTP + CoA + 3\ H^+$$

Question 8

Which of the following best describes the effect of ATP on metabolic flux through the citrate cycle?

Accepted Answer

ATP decreases the flux by inhibiting key enzymes, reflecting high energy status.

Question 9

Pyruvate carboxylase catalyzes the following reaction to supply oxaloacetate to the citrate cycle. Which equation represents this reaction?

Accepted Answer

$$\mathrm{Pyruvate} + CO_2$ + ATP \rightarrow \mathrm{Oxaloacetate} + ADP + P_i$$

Question 10

Which experiment provided evidence for the Chemiosmotic Theory?

Accepted Answer

Racker and Stoeckenius reconstituted ATP synthase and bacteriorhodopsin in artificial vesicles, showing ATP synthesis driven by light-induced proton gradients.

Question 11

Which equation would you use to calculate the standard free energy change ($$\Delta G$$^{\circ'}$$) for a redox reaction using reduction potentials?

Accepted Answer

$$\Delta G$$^{\circ'}$$ = -nF\Delta E$$^{\circ'}$$

Question 12

Which enzyme is responsible for transferring electrons from NADH to the electron transport chain?

Accepted Answer

NADH:ubiquinone oxidoreductase (Complex I)

Question 13

Which of the following statements about ATP synthase is correct?

Accepted Answer

ATP synthase consists of F0 and F1 subunits, with F0 forming the proton channel and F1 catalyzing ATP synthesis.

Question 14

Which principle is NOT part of the binding change mechanism of ATP synthase?

Accepted Answer

ATP is synthesized only when the enzyme is in the open conformation.

Question 15

How are ADP, ATP, and Pi transported across the inner mitochondrial membrane?

Accepted Answer

By specific transport proteins: the adenine nucleotide translocase for ADP/ATP and the phosphate transporter for Pi.

Question 16

Which mechanism is used to transfer electrons from cytosolic NADH into the mitochondrial matrix in muscle cells?

Accepted Answer

Glycerol-3-phosphate shuttle

Question 17

Which compound acts as an uncoupler of oxidative phosphorylation, and what is its effect?

Accepted Answer

2,4-dinitrophenol; it dissipates the proton gradient, reducing ATP synthesis and increasing heat production.

Question 18

Why are mitochondrial disorders inherited only through the maternal line?

Accepted Answer

Mitochondria in the zygote are derived exclusively from the egg cell.

Question 19

Thermogenin (UCP1) provides adaptive survival in certain animals by:

Accepted Answer

Allowing protons to re-enter the mitochondrial matrix without ATP synthesis, generating heat.

Krebs Cycle, Oxidative Phosphorylation, and ATP Synthesis: Study Guide

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