This set of Microbiology Multiple Choice Questions & Answers (MCQs) focuses on “Energy Production by Aerobic Processes”.
1. The TCA Cycle is an _____________ pathway.
Explanation: The TCA cycle is an amphibolic cycle which means that it functions not only in catabolic (breakdown) but also in anabolic (synthesis) reactions.
2. Which of the following intermediates of TCA cycle act as amino acid precursors?
a) oxaloacetic acid
b) succinic acid
c) citric acid
d) acetyl CoA
Explanation: Oxaloacetic acid and alpha-ketoglutaric acid are some of the intermediates of TCA cycle which act as amino acid precursors.Oxaloacetate forms aspartate which then gives us lysine and threonine.
3. Which pathway will result in the production of four carbon dioxide molecules, two ATP molecules, NADH2 and FADH2?
b) Krebs cycle
c) Calvin cycle
d) electron transport system
Explanation: Krebs Cycle is another name for TCA cycle whose overall reaction is as follows:
2Acetyl CoA+ 3H2O + 3NAD+ + FAD+ ADP+ Pi———> 4CO2+ 2CoA+ 2NADH2+ 2FADH2+ ATP.
4. The TCA cycle is regulated by which of the following enzymes?
a) citrate synthase
b) isocitrate dehydrogenase
c) malate dehydrogenase
d) succinate dehydrogenase
Explanation: TCA cycle is regulated by the enzyme isocitrate dehydrogenase which is sensitive to feedback inhibition by high concentration of ATP and NADH2 and stimulation by high concentration of ADP and NAD.
5. Protein molecules can easily pass into the cell for being utilized for energy production.
Explanation: Protein molecules are too large to pass into the cell, bacteria secrete exoenzymes called proteases that hydrolyze exogenous proteins to peptides, which are then transported into the cell cytoplasm.
6. Which of the following pathway is common for oxidation of carbohydrates, lipids and amino acids?
a) Calvin cycle
b) Electron transport chain
c) TCA cycle
d) Pentose phosphate pathway
Explanation: Since acetyl-CoA is a common intermediate of carbohydrate, lipid, and amino acid metabolism so it enters the TCA cycle and hence TCA cycle is a common pathway for oxidation of carbohydrates, lipids and amino acids.
7. Phosphoenolpyruvate (PEP) is converted to oxaloacetate by the enzyme PEP deaminase.
Explanation: PEP is converted to oxaloacetate by the enzyme PEP carboxylase. This is a type of carbon dioxide fixing reaction.
8. The enzymes present in glyoxylate cycle are which type of enzymes?
a) reductase enzymes
b) anaplerotic enzymes
c) transferase enzymes
d) hydrolase enzymes
Explanation: The specific enzymes for glyoxalate cycle are isocitrate lyase and malate synthase which carry out replenishment of the pool of intermediates of the TCA cycle and hence are known as anaplerotic enzymes.
9. Which molecule will combine with the four-carbon oxaloacetate in the TCA cycle to form the six-carbon citrate?
a) lactic acid
Explanation: The first step of the TCA cycle is the reaction between oxaloacetate and acetyl-CoA to form citrate. This acetyl-CoA comes from carbohydrate, lipid metabolism.
10. The number of ATP molecules generated in TCA cycle is _________
Explanation: In TCA cycle the following result is obtained:
6 NADH2 —> 18 ATP
2 FADH2 —> 4 ATP
2 GTP —> 2 ATP
Thus, total ATP = 24 ATP.
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