Question 1

An in vitro study shows that isocitrate dehydrogenase is activated in the citrate cycle. What is a possible explanation for the activation?

Accepted Answer

A)  high levels of ATP 
B)  low levels of ATP 
C)  high levels of NADH 
D)  low levels of AMP 
A)  high levels of ATP 
B)  low levels of ATP 
C)  high levels of NADH 
D)  low levels of AMP B

Question 2

If acetyl-CoA is not metabolized by the citrate cycle, the molecule in the cell

Accepted Answer

A)  undergoes fatty acid metabolism. 
B)  is transported across the cell membrane. 
C)  is used to synthesize amino acids. 
D)  is used during glycolysis. 
A)  undergoes fatty acid metabolism. 
B)  is transported across the cell membrane. 
C)  is used to synthesize amino acids. 
D)  is used during glycolysis. A

Question 3

Pantothenic acid is essential for life because it is the vitamin precursor to the molecule that

Accepted Answer

A)  provides a reactive disulfide that can participate in redox reactions within the enzyme active site of pyruvate dehydrogenase. 
B)  can accept one or two electrons in redox reactions in the cell. 
C)  is involved in at least 200 redox reactions in the cell. 
D)  is a cofactor in the biosynthetic pathways that produce fatty acids, acetylcholine, heme, and cholesterol. 
A)  provides a reactive disulfide that can participate in redox reactions within the enzyme active site of pyruvate dehydrogenase. 
B)  can accept one or two electrons in redox reactions in the cell. 
C)  is involved in at least 200 redox reactions in the cell. 
D)  is a cofactor in the biosynthetic pathways that produce fatty acids, acetylcholine, heme, and cholesterol. D

Question 4

Which enzyme regulates the flux of acetyl-CoA through the citrate cycle?

Accepted Answer

A)  "pyruvate dehydrogenase" 
B)  "citrate synthase" 
C)  "isocitrate dehydrogenase" 
D)  "$\alpha$-ketoglutarate dehydrogenase" 
A)  "pyruvate dehydrogenase" 
B)  "citrate synthase" 
C)  "isocitrate dehydrogenase" 
D)  "$\alpha$-ketoglutarate dehydrogenase"

Question 5

An in vitro study shows that citrate synthase is inhibited in the citrate cycle. What is a possible explanation for this inhibition?

Accepted Answer

A)  high levels of ADP 
B)  low levels of succinyl-CoA 
C)  high levels of NADH 
D)  high levels of AMP 
A)  high levels of ADP 
B)  low levels of succinyl-CoA 
C)  high levels of NADH 
D)  high levels of AMP

Question 6

What two features of the citrate cycle make it unique compared with linear metabolic pathways?

Accepted Answer

Oxaloacetate is both the substrate for t

Question 7

Using the table below, calculate $\Delta$G $\degree$'  and determine if the conversion from malate to oxaloacetate is favorable under standard biochemical conditions.
Malate + NAD+ $\rightarrow$  Oxaloacetate + H+ + NADH

Accepted Answer

Calculate the@#LAT-DLM&E for the coupled redox rea

Question 8

The citrate cycle is considered to be a(n) pathway.

Accepted Answer

A)  anabolic 
B)  catabolic 
C)  anaplerotic 
D)  amphibolic 
A)  anabolic 
B)  catabolic 
C)  anaplerotic 
D)  amphibolic

Question 9

Calculate the $\Delta$E $\degree$'  of a coupled redox reaction with O2 and ferredoxin (Fe2+) using the table below.

Accepted Answer

A)  "-1.25" 
B)  "-0.39" 
C)  "0.39" 
D)  "1.25" 
A)  "-1.25" 
B)  "-0.39" 
C)  "0.39" 
D)  "1.25"

Question 10

According to the $\Delta$G $\degree$' , which of the following exergonic reactions is most likely irreversible under normal cellular conditions and is considered to be the rate-limiting step of the citrate cycle?

Accepted Answer

A)  "citrate synthase" 
B)  "fumarase" 
C)  "isocitrate dehydrogenase" 
D)  "$\alpha$-ketoglutarate dehydrogenase" 
A)  "citrate synthase" 
B)  "fumarase" 
C)  "isocitrate dehydrogenase" 
D)  "$\alpha$-ketoglutarate dehydrogenase"

Question 11

Which enzyme in the citrate cycle produces NADH?

Accepted Answer

A)  aconitase 
B)  citrate synthase 
C)  isocitrate dehydrogenase 
D)  fumarase 
A)  aconitase 
B)  citrate synthase 
C)  isocitrate dehydrogenase 
D)  fumarase

Question 12

Identify the strongest reductant in the table below.

Accepted Answer

A)  O2 
B)  oxaloacetate 
C)  pyruvate 
D)  ferredoxin 
A)  O2 
B)  oxaloacetate 
C)  pyruvate 
D)  ferredoxin

Question 13

The primary function of the citrate cycle is to oxidize

Accepted Answer

A)  glucose. 
B)  pyruvate. 
C)  acetyl-CoA. 
D)  citrate. 
A)  glucose. 
B)  pyruvate. 
C)  acetyl-CoA. 
D)  citrate.

Question 14

Compare the two ways the pyruvate dehydrogenase reaction is controlled by the cell.

Accepted Answer

Pyruvate dehydrogenase is regulated by a

Question 15

What is the purpose of the first 3 steps in the pyruvate dehydrogenase reaction?

Accepted Answer

A)  regenerate the oxidized form of lipoamide 
B)  form NADH 
C)  transfer electrons 
D)  form acetyl-CoA 
A)  regenerate the oxidized form of lipoamide 
B)  form NADH 
C)  transfer electrons 
D)  form acetyl-CoA

Question 16

Which reaction in the citrate cycle produces CO2?

Accepted Answer

A)  1 
B)  2 
C)  3 
D)  5 
A)  1 
B)  2 
C)  3 
D)  5

Question 17

Which vitamin is the precursor to the coenzyme that functions as a reductant in the pyruvate dehydrogenase complex in the final step of the reaction?

Accepted Answer

A)  thiamine 
B)  pantothenic acid 
C)  riboflavin 
D)  niacin 
A)  thiamine 
B)  pantothenic acid 
C)  riboflavin 
D)  niacin

Question 18

Classify the reaction that occurs at step 1 in the reaction schematic of the pyruvate dehydrogenase reaction below.

Accepted Answer

A)  isomerization 
B)  addition 
C)  oxidation reduction 
D)  decarboxylation 
A)  isomerization 
B)  addition 
C)  oxidation reduction 
D)  decarboxylation

Question 19

A high NADH to NAD+ ratio would inhibit which enzyme in the citrate cycle?

Accepted Answer

A)  succinate dehydrogenase 
B)  succinyl-CoA synthetase 
C)  aconitase 
D)  isocitrate dehydrogenase 
A)  succinate dehydrogenase 
B)  succinyl-CoA synthetase 
C)  aconitase 
D)  isocitrate dehydrogenase

Question 20

Use the overall net reaction of the citrate cycle to explain why excess NADH inhibits the pyruvate dehydrogenase reaction.

Accepted Answer

NADH is a product in the balanced citrat

Exam 10: The Citrate Cycle

An in vitro study shows that isocitrate dehydrogenase is activated in the citrate cycle. What is a possible explanation for the activation?

If acetyl-CoA is not metabolized by the citrate cycle, the molecule in the cell

Pantothenic acid is essential for life because it is the vitamin precursor to the molecule that

Which enzyme regulates the flux of acetyl-CoA through the citrate cycle?

An in vitro study shows that citrate synthase is inhibited in the citrate cycle. What is a possible explanation for this inhibition?

What two features of the citrate cycle make it unique compared with linear metabolic pathways?

Using the table below, calculate Δ\DeltaΔ G °\degree° ' and determine if the conversion from malate to oxaloacetate is favorable under standard biochemical conditions. Malate + NAD+ →\rightarrow→ Oxaloacetate + H+ + NADH

The citrate cycle is considered to be a(n) pathway.

Calculate the Δ\DeltaΔ E °\degree° ' of a coupled redox reaction with O2 and ferredoxin (Fe2+) using the table below.

According to the Δ\DeltaΔ G °\degree° ' , which of the following exergonic reactions is most likely irreversible under normal cellular conditions and is considered to be the rate-limiting step of the citrate cycle?

Which enzyme in the citrate cycle produces NADH?

Identify the strongest reductant in the table below.

The primary function of the citrate cycle is to oxidize

Compare the two ways the pyruvate dehydrogenase reaction is controlled by the cell.

What is the purpose of the first 3 steps in the pyruvate dehydrogenase reaction?

Which reaction in the citrate cycle produces CO2?

Which vitamin is the precursor to the coenzyme that functions as a reductant in the pyruvate dehydrogenase complex in the final step of the reaction?

Classify the reaction that occurs at step 1 in the reaction schematic of the pyruvate dehydrogenase reaction below.

A high NADH to NAD+ ratio would inhibit which enzyme in the citrate cycle?

Use the overall net reaction of the citrate cycle to explain why excess NADH inhibits the pyruvate dehydrogenase reaction.

Principles of Biochemistry

Physical Biochemistry: Energy Conversion, Water, and Membranes

Nucleic Acid Structure and Function

Protein Structure

Methods in Protein Biochemistry

Protein Function

Enzyme Mechanisms

Cell Signaling Systems

Glycolysis: a Paradigm of Metabolic Regulation

Oxidative Phosphorylation

Photosynthesis

Carbohydrate Structure and Function

Carbohydrate Metabolism

Lipid Structure and Function

Lipid Metabolism

Amino Acid Metabolism

Nucleotide Metabolism

Metabolic Integration

DNA Replication, Repair, and Recombination

RNA Synthesis, Processing, and Gene Silencing

Protein Synthesis, Posttranslational Modification, and Transport

Gene Regulation

Filters

Calculate the $\Delta$ E $\degree$ ^' of a coupled redox reaction with O₂ and ferredoxin (Fe²⁺) using the table below. $Calculate the \Delta E \degree <sup>'</sup> <sup> </sup>of a coupled redox reaction with O<sub>2</sub> and ferredoxin (Fe<sup>2+</sup>) using the table below.$

According to the $\Delta$ G $\degree$ ^' , which of the following exergonic reactions is most likely irreversible under normal cellular conditions and is considered to be the rate-limiting step of the citrate cycle?

Which reaction in the citrate cycle produces CO₂?

A high NADH to NAD⁺ratio would inhibit which enzyme in the citrate cycle?