Acetyl CoA & TCA Cycle

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| By Iyanna Peppers

Iyanna Peppers

Community Contributor

Quizzes Created: 3 | Total Attempts: 1,777

Questions: 14 | Attempts: 405 | Updated: Mar 21, 2023

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Questions and Answers

1.

Pyruvate dehydrogenase complex catalyzes the:
- A.
  
  Oxidative decarboxylation of pyruvate to CO₂ and acetyl CoA
- B.
  
  Citrate to isocitrate reaction
- C.
  
  Addition of a carboxylic acid to pyruvate, forming oxaloacetate
- D.
  
  Formation of fumarate and FADH2 from succinate
Correct Answer
A. Oxidative decarboxylation of pyruvate to CO₂ and acetyl CoA

Explanation
The correct answer is the oxidative decarboxylation of pyruvate to CO2 and acetyl CoA. The pyruvate dehydrogenase complex is responsible for converting pyruvate, a product of glycolysis, into acetyl CoA, which is a crucial molecule in the citric acid cycle. This process involves the removal of a carboxyl group from pyruvate, resulting in the release of CO2, and the remaining acetyl group is transferred to Coenzyme A (CoA) to form acetyl CoA. This reaction generates high-energy electrons that are captured by NAD+ to produce NADH, which can then be used in oxidative phosphorylation to generate ATP.

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2.

1 mole of pyruvate to acetyl-CoA yields ___ mole(s) of NADH.
- A.
  
  1
- B.
  
  2
- C.
  
  4
- D.
  
  3
Correct Answer
A. 1

Explanation
When 1 mole of pyruvate is converted into acetyl-CoA, it produces 1 mole of NADH. This is because during the conversion process, one molecule of NAD+ is reduced to NADH. Therefore, the correct answer is 1.

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3.

Which cofactors of the pyruvate dehydrogenase reaction are permanently bound?
- A.
  
  Thiamine pyrophosphate
- B.
  
  Lipoamide
- C.
  
  Flavin adenine dinucleotide
- D.
  
  Nicotinamide adenine dinucleotide
- E.
  
  Coenzyme A
Correct Answer(s)
A. Thiamine pyrophosphate
B. Lipoamide
C. Flavin adenine dinucleotide

Explanation
Thiamine pyrophosphate, lipoamide, and flavin adenine dinucleotide are permanently bound cofactors in the pyruvate dehydrogenase reaction. This means that they are tightly bound to the enzyme and participate in the reaction without being released or consumed. These cofactors play essential roles in catalyzing the conversion of pyruvate to acetyl-CoA, which is an important step in cellular respiration. Thiamine pyrophosphate is involved in decarboxylation reactions, lipoamide acts as a carrier of acetyl groups, and flavin adenine dinucleotide is a redox cofactor.

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4.

Which pyruvate dehydrogenase cofactors are acyl group carriers?
- A.
  
  Coenzyme A
- B.
  
  Lipoamide
- C.
  
  FAD
- D.
  
  NAD+
- E.
  
  TPP
Correct Answer(s)
A. Coenzyme A
B. Lipoamide

Explanation
Coenzyme A and lipoamide are the acyl group carriers in the pyruvate dehydrogenase complex. Coenzyme A carries the acetyl group, while lipoamide carries the other acyl groups, such as the succinyl and propionyl groups. FAD and NAD+ are electron carriers, and TPP (thiamine pyrophosphate) is a coenzyme involved in decarboxylation reactions. Therefore, the correct answer is Coenzyme A and lipoamide.

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5.

Molecules with ____, such as dihydrolipoamide, are targets for covalent modification by arsenite.
- A.
  
  Proximal thiols
- B.
  
  Distal thiols
- C.
  
  Proximal hydroxyls
- D.
  
  Distal hydroxyls
Correct Answer
A. Proximal thiols

Explanation
Molecules with proximal thiols, such as dihydrolipoamide, are targets for covalent modification by arsenite. This means that arsenite can form a covalent bond with the proximal thiols in dihydrolipoamide, leading to a chemical modification of the molecule. Proximal thiols are sulfur-containing groups that are located close to the active site of the molecule, making them susceptible to interaction with arsenite. This interaction can have various effects on the function and structure of the molecule, potentially leading to biological consequences.

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6.

______ is complex II of the mitochondrial electron transport chain.
- A.
  
  Succinate dehydrogenase
- B.
  
  Malate dehydrogenase
- C.
  
  α-ketoglutarate dehydrogenase
- D.
  
  Aconitase
Correct Answer
A. Succinate dehydrogenase

Explanation
Succinate dehydrogenase is complex II of the mitochondrial electron transport chain. It is responsible for transferring electrons from succinate to ubiquinone, which is a crucial step in the production of ATP. This enzyme is embedded in the inner mitochondrial membrane and plays a key role in the oxidation of succinate, a substrate derived from the citric acid cycle.

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7.

____ and _____ inhibit key steps of the TCA cycle.
- A.
  
  ATP; NADH
- B.
  
  NAD⁺; ADP
- C.
  
  Succinyl CoA; ADP
- D.
  
  ATP: NAD⁺
Correct Answer
A. ATP; NADH

Explanation
ATP and NADH inhibit key steps of the TCA cycle. ATP is a high-energy molecule that is produced during cellular respiration and is used as a source of energy for various cellular processes. When ATP levels are high, it indicates that the cell has sufficient energy and can inhibit the TCA cycle to prevent excessive production of ATP. NADH, on the other hand, is an electron carrier molecule that is generated during the breakdown of glucose. High levels of NADH indicate that the cell has sufficient energy and can also inhibit the TCA cycle to prevent excessive production of NADH.

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8.

Which PRODUCTS are not formed when there is an excess of ATP and NADH?
- A.
  
  Acetyl CoA
- B.
  
  α-ketoglutarate
- C.
  
  Succinyl-CoA
- D.
  
  Isocitrate
- E.
  
  Pyruvate
Correct Answer(s)
A. Acetyl CoA
B. α-ketoglutarate
C. Succinyl-CoA

Explanation
When there is an excess of ATP and NADH, the citric acid cycle (also known as the Krebs cycle) slows down. Acetyl CoA, α-ketoglutarate, and succinyl-CoA are all intermediates in the citric acid cycle, which means they are produced and consumed during the cycle. However, when there is an excess of ATP and NADH, the cycle slows down and fewer intermediates are formed. Therefore, Acetyl CoA, α-ketoglutarate, and succinyl-CoA are not formed in sufficient quantities when there is an excess of ATP and NADH.

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9.

Catabolic action yields:
- A.
  
  High energy metabolites
- B.
  
  New material (ie, amino acids, porphyrins)
Correct Answer
A. High energy metabolites

Explanation
Catabolic action refers to the breakdown of complex molecules into simpler ones. This process releases energy, which is stored in high energy metabolites. These metabolites, such as ATP, can be used by the cell for various energy-requiring processes. Additionally, catabolic action also produces new materials like amino acids and porphyrins, which can be used for the synthesis of proteins and other essential molecules in the cell.

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10.

The TCA cycle is considered to be anapleurotic. This describes:
- A.
  
  That there are multiple points around the cycle where reactants feed in.
- B.
  
  The circular, regenerative nature of the TCA cycle.
- C.
  
  That malate is the only TCA cycle product that can be shunted through the mitochondrial membrane.
- D.
  
  That the TCA cycle is reversible when needed.
Correct Answer
A. That there are multiple points around the cycle where reactants feed in.

Explanation
The TCA cycle is considered to be anapleurotic because there are multiple points around the cycle where reactants can enter. This means that the cycle can be replenished with intermediates from other metabolic pathways, ensuring a constant supply of reactants for energy production. This flexibility allows the TCA cycle to adapt to changing metabolic demands and maintain its function as a central hub in cellular metabolism.

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Current Version
Mar 21, 2023

Quiz Edited by
ProProfs Editorial Team
Aug 05, 2020

Quiz Created by
Iyanna Peppers

Acetyl Coa & Tca Cycle

Pyruvate dehydrogenase complex catalyzes the:

1 mole of pyruvate to acetyl-CoA yields ___ mole(s) of NADH.

Which cofactors of the pyruvate dehydrogenase reaction are permanently bound?

Which pyruvate dehydrogenase cofactors are acyl group carriers?

Molecules with ____, such as dihydrolipoamide, are targets for covalent modification by arsenite.

______ is complex II of the mitochondrial electron transport chain.

and _ inhibit key steps of the TCA cycle.

Which PRODUCTS are not formed when there is an excess of ATP and NADH?

Catabolic action yields:

The TCA cycle is considered to be anapleurotic. This describes: