Q: Which of the following equations correctly summarizes the overall reaction of the citric acid cycle per acetyl-CoA molecule?

$\text{acetyl-CoA} + 3\text{NAD}^+ + \text{FAD} + \text{ADP} + P_i \rightarrow 2\text{CO}_2 + 3\text{NADH} + \text{FADH}_2 + \text{CoA-SH} + \text{ATP}$

Question 1

Which of the following best describes the main function of the electron transport chain (ETC) in mitochondria?

Accepted Answer

To transfer electrons from reduced coenzymes to oxygen, creating a proton gradient across the inner mitochondrial membrane.

Question 2

During aerobic respiration, what is the primary role of oxygen?

Accepted Answer

To serve as the terminal electron acceptor in the electron transport chain, forming water.

Question 3

Which of the following equations correctly summarizes the overall reaction of the citric acid cycle per acetyl-CoA molecule?

Accepted Answer

$	ext{acetyl-CoA} + 3	ext{NAD}^+ + 	ext{FAD} + 	ext{ADP} + P_i ightarrow 2	ext{CO}_2 + 3	ext{NADH} + 	ext{FADH}_2 + 	ext{CoA-SH} + 	ext{ATP}$

Question 4

A mutation in Complex I of the electron transport chain prevents it from pumping protons. How many protons would be pumped into the intermembrane space per NADH oxidized in this mutant?

Accepted Answer

6 protons

Question 5

Which of the following statements about mitochondrial protein import is correct?

Accepted Answer

Most mitochondrial proteins are encoded by nuclear DNA, synthesized in the cytosol, and imported into mitochondria via TOM and TIM complexes.

Question 6

Which of the following best explains why the theoretical maximum yield of ATP per glucose molecule during aerobic respiration is rarely achieved in eukaryotic cells?

Accepted Answer

Some protons are used for processes other than ATP synthesis, and the transport of cytosolic NADH electrons into mitochondria is not 100% efficient.

Question 7

Which of the following is a correct description of the chemiosmotic model proposed by Peter Mitchell?

Accepted Answer

The energy from electron transport is used to pump protons across the inner mitochondrial membrane, creating an electrochemical gradient that drives ATP synthesis.

Question 8

Which of the following best describes the function of the F$_0$F$_1$ ATP synthase complex?

Accepted Answer

It couples the flow of protons down their electrochemical gradient to the synthesis of ATP from ADP and P$_i$.

Question 9

Which of the following is a product of the incomplete reduction of oxygen by complexes I and III of the electron transport chain, and what is its significance?

Accepted Answer

Superoxide anion (O$_2^-$), which is a reactive oxygen species that can contribute to cellular aging.

Question 10

In the binding change model for ATP synthesis, what is the role of the rotation of the γ (gamma) subunit within the F$_1$ complex?

Accepted Answer

It causes conformational changes in the β subunits, cycling them through loose (L), tight (T), and open (O) states to facilitate ATP synthesis and release.

Question 11

Which of the following statements about the citric acid cycle is correct?

Accepted Answer

It generates reduced coenzymes (NADH and FADH$_2$) that feed electrons into the electron transport chain.

Question 12

If a cell is exposed to cyanide, which inhibits cytochrome c oxidase (Complex IV), what is the most immediate effect on cellular respiration?

Accepted Answer

Electron transport halts, preventing the reduction of oxygen to water and stopping ATP synthesis by oxidative phosphorylation.

Question 13

Which of the following best explains why FADH$_2$ yields less ATP than NADH during oxidative phosphorylation?

Accepted Answer

Electrons from FADH$_2$ enter the electron transport chain at Complex II, bypassing Complex I and resulting in fewer protons being pumped across the membrane.

Question 14

Which of the following is a correct summary of the maximum theoretical ATP yield per glucose molecule during aerobic respiration in eukaryotic cells?

Accepted Answer

38 ATP

Question 15

Which of the following is a key regulatory mechanism of the citric acid cycle?

Accepted Answer

Allosteric inhibition of key enzymes by NADH, ATP, and acetyl-CoA.

Question 16

A patient has a genetic defect that prevents the removal of the transit sequence from mitochondrial precursor proteins. What is the most likely consequence?

Accepted Answer

Proteins will accumulate in the mitochondrial matrix with their transit sequences still attached, potentially interfering with proper folding and function.

Question 17

How many protons must pass through the F$_0$F$_1$ ATPase to synthesize one molecule of ATP, assuming 2.5 ATP are generated per NADH and 10 protons are pumped per NADH?

Accepted Answer

4 protons

Question 18

Which of the following best describes the role of chaperone proteins such as Hsp70 and Hsp60 in mitochondrial protein import?

Accepted Answer

They bind to polypeptides to maintain them in an unfolded state for import and assist in proper folding once inside the matrix.

Question 19

Which of the following is a real-world consequence of the generation of reactive oxygen species (ROS) by the electron transport chain?

Accepted Answer

ROS such as superoxide anion and hydrogen peroxide can damage cellular components, contributing to aging and disease.

Cellular Respiration and Mitochondrial Function: Key Concepts and Mechanisms

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