This set of Cell Biology Multiple Choice Questions & Answers (MCQs) focuses on “Aerobic Respiration – TCA Cycle”.
1. All enzymes of the TCA cycle reside in the mitochondrial membrane.
Explanation: All enzymes of the TCA cycle other than succinate dehydrogenase reside in the matrix. It is the only enzyme that takes part in both TCA cycle and electron transport chain and it resides in the inner mitochondrial membrane.
2. Which of the following is also known as Krebs cycle?
a) Electron transport chain
c) TCA cycle
d) DNA Replication
Explanation: The TCA cycle is also known as the Krebs cycle after the name of British biochemist Hans Kreb who elucidated the pathway in 1930s.
3. How many reactions that occur in the TCA cycle transfer electrons from a substrate to an electron accepting enzyme?
Explanation: There are four such a reaction in which electron is transferred from substrate to electron accepting enzyme. In three of these, NAD+ is reduced to NADH and in one FAD reduces to FADH2.
4. Which of the following is an important end product of disassembly of fatty acids?
a) Acetyl CoA
b) Succinate dehydrogenase
d) DNA gyrase
Explanation: The metabolites of TCA cycle are also the same compounds generated by other catabolic processes in the cell. For instance, Acetyl CoA is also an important end product of disassembly of fatty acids.
5. Polysaccharides, fats and proteins break down into metabolites of __________________
b) TCA cycle
c) RNA repair
d) Membrane synthesis
Explanation: Mitochondrion is the site for final energy-conserving steps in metabolism. The energy providing macromolecules polysaccharides, fats and proteins break down into the metabolites of TCA cycle.
6. Acetyl CoA is a _____________ carbon compound.
Explanation: Acetyl CoA is a 2 carbon compound. From oxidation of pyruvate (by the pyruvate dehydrogenase) which is a 3 carbon compound, acetyl CoA is formed with the release of one molecule of CO2 and NADH each.
7. In the TCA cycle, which of the following combines with Acetyl CoA to form a 6 carbon compound?
Explanation: Acetyl CoA is a 2 carbon compound that combines with oxaloacetate which is a 4 carbon compound to form a 6 carbon compound, citrate. The reaction is catalyzed by citrate synthase.
8. The enzyme aconitase is responsible for ________________
Explanation: In the TCA cycle, aconitase is responsible for isomerization of citrate to isocitrate. Isocitrate is further oxidized by isocitrate dehydrogenase to form alpha-ketoglutarate.
9. For each molecule of glucose, how many times does the TCA cycle proceed?
Explanation: Since each molecule of glucose gives off two pyruvate molecules through the process of glycolysis, the cycle operates twice for each molecule of glucose.
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