Question 1

Which enzyme class is NOT found in the citric acid cycle?

Accepted Answer

A)  oxidoreductase 
B)  hydrolase 
C)  ligase 
D)  lyase 
E)  isomerase 
A)  oxidoreductase 
B)  hydrolase 
C)  ligase 
D)  lyase 
E)  isomerase B

Question 2

Briefly describe the relationship of the pyruvate dehydrogenase complex reaction to glycolysis and the citric acid cycle.

Accepted Answer

The pyruvate dehydrogenase complex (PDC) reaction is a crucial link between glycolysis and the citric acid cycle. In glycolysis, glucose is broken down into pyruvate, which is then converted to acetyl-CoA by the PDC. Acetyl-CoA is the starting molecule for the citric acid cycle, where it undergoes a series of reactions to produce ATP, NADH, and FADH2. Therefore, the PDC reaction connects the breakdown of glucose in glycolysis to the energy-producing reactions of the citric acid cycle, making it an essential step in cellular respiration.

Question 3

How many ATP equivalents are made from the aerobic conversion of pyruvate to oxaloacetate?

Accepted Answer

A)  9 ATP 
B)  10 ATP 
C)  11 ATP 
D)  11.5 ATP 
E)  12.5 ATP 
A)  9 ATP 
B)  10 ATP 
C)  11 ATP 
D)  11.5 ATP 
E)  12.5 ATP E

Question 4

Which three of the choices listed are possible sources for acetyl-CoA that enters the citric acid cycle? 
1. oxidative decarboxylation of pyruvate
2. β oxidation of fatty acids
3. catabolism of certain amino acids
4. citrate
5. carboxylation of pyruvate

Accepted Answer

A) 	1, 2, and 3 
B) 	1, 2, and 4 
C) 	1, 2, and 5 
D) 	1, 4, and 4 
E) 	2, 4, and 5 
A) 	1, 2, and 3 
B) 	1, 2, and 4 
C) 	1, 2, and 5 
D) 	1, 4, and 4 
E) 	2, 4, and 5

Question 5

The pyruvate dehydrogenase complex catalyzes the oxidative decarboxylation of pyruvate. Two of the steps catalyzed by this complex do not involve any of the carbons of pyruvate. Briefly describe these reaction steps.

Accepted Answer

The pyruvate dehydrogenase complex (PDC)

Question 6

Show the steps of the citric acid cycle in which a six-carbon compound is converted into the first four-carbon intermediate in the path. For each step, show structures of substrate and product, name the enzyme responsible, and show where cofactors participate.

Accepted Answer

The citric acid cycle, also known as the

Question 7

Which cofactors associated with the pyruvate dehydrogenase complex are classified as prosthetic groups? 1) TPP
2) lipoate
3) CoA-SH
4) NAD+
5) FAD

Accepted Answer

A)  1 and 5 
B)  1, 2, and 4 
C)  1, 2, and 5 
D)  3 and 4 
E)  4 and 5 
A)  1 and 5 
B)  1, 2, and 4 
C)  1, 2, and 5 
D)  3 and 4 
E)  4 and 5

Question 8

Show the reactions by which $\alpha$-ketoglutarate is converted to malate in the citric acid cycle.

Accepted Answer

The conversion of @#LAT-DLM&-ketoglutarate to mala

Question 9

Show the steps of the citric acid cycle from succinyl-CoA to oxaloacetate only. For each step, show structures of substrate and product, name the enzyme responsible, and show where cofactors participate.

Accepted Answer

Step 1: Succinyl-CoA is converted to suc

Question 10

Which enzymes catalyze oxidation reactions in the citric acid cycle? 1) succinate dehydrogenase
2) pyruvate dehydrogenase
3) citrate dehydrogenase
4) $\alpha$-ketoglutarate dehydrogenase

Accepted Answer

A)  1 and 4 
B)  1, 2, and 4 
C)  1, 3, and 4 
D)  2 and 3 
E)  All of the listed enzymes catalyze oxidation reactions in the citric acid cycle. 
A)  1 and 4 
B)  1, 2, and 4 
C)  1, 3, and 4 
D)  2 and 3 
E)  All of the listed enzymes catalyze oxidation reactions in the citric acid cycle.

Question 11

During seed germination, the glyoxylate pathway is important to plants because it enables them to:

Accepted Answer

A)  carry out the net synthesis of glucose from acetyl-CoA. 
B)  form acetyl-CoA from malate. 
C)  get rid of isocitrate formed from the aconitase reaction. 
D)  obtain glyoxylate for cholesterol biosynthesis. 
E)  obtain glyoxylate for pyrimidine synthesis. 
A)  carry out the net synthesis of glucose from acetyl-CoA. 
B)  form acetyl-CoA from malate. 
C)  get rid of isocitrate formed from the aconitase reaction. 
D)  obtain glyoxylate for cholesterol biosynthesis. 
E)  obtain glyoxylate for pyrimidine synthesis.

Question 12

Citrate synthase and the NAD+-specific isocitrate dehydrogenase are two key regulatory enzymes of the citric acid cycle. These enzymes are inhibited by:

Accepted Answer

A)  acetyl-CoA and fructose 6-phosphate. 
B)  AMP and/or NAD+. 
C)  AMP and/or NADH. 
D)  ATP and/or NAD+. 
E)  ATP and/or NADH. 
A)  acetyl-CoA and fructose 6-phosphate. 
B)  AMP and/or NAD+. 
C)  AMP and/or NADH. 
D)  ATP and/or NAD+. 
E)  ATP and/or NADH.

Question 13

Which type of reaction is found in the citric acid cycle?

Accepted Answer

A)  isomerization 
B)  hydration 
C)  condensation 
D)  redox 
E)  All of the answers are correct. 
A)  isomerization 
B)  hydration 
C)  condensation 
D)  redox 
E)  All of the answers are correct.

Question 14

Intermediates in the citric acid cycle are used as precursors in the biosynthesis of:

Accepted Answer

A)  amino acids. 
B)  nucleotides. 
C)  fatty acids. 
D)  sterols. 
E)  All of the answers are correct. 
A)  amino acids. 
B)  nucleotides. 
C)  fatty acids. 
D)  sterols. 
E)  All of the answers are correct.

Question 15

What is the function of FAD in the pyruvate dehydrogenase complex? How is it regenerated?

Accepted Answer

FAD, or flavin adenine dinucleotide, ser

Question 16

Which reaction in the citric acid cycle will NOT proceed in the absence of inorganic phosphate ions?

Accepted Answer

A)  the reaction catalyzed by $\alpha$-ketoglutarate dehydrogenase 
B)  the reaction catalyzed by succinate dehydrogenase 
C)  the reaction catalyzed by succinyl-CoA synthetase 
D)  the reaction catalyzed by aconitase 
E)  the reaction catalyzed by fumarase 
A)  the reaction catalyzed by $\alpha$-ketoglutarate dehydrogenase 
B)  the reaction catalyzed by succinate dehydrogenase 
C)  the reaction catalyzed by succinyl-CoA synthetase 
D)  the reaction catalyzed by aconitase 
E)  the reaction catalyzed by fumarase

Question 17

Which cofactor is required for the conversion of fumarate to succinate?

Accepted Answer

A)  FAD 
B)  GDP 
C)  CoA 
D)  FADH2 
E)  both GDP and CoA 
A)  FAD 
B)  GDP 
C)  CoA 
D)  FADH2 
E)  both GDP and CoA

Question 18

A function of the glyoxylate cycle, in conjunction with the citric acid cycle, is to accomplish:

Accepted Answer

A)  the complete oxidation of acetyl-CoA to CO2 plus reduced coenzymes. 
B)  the net conversion of lipid to carbohydrate. 
C)  the net synthesis of four-carbon dicarboxylic acids from acetyl-CoA. 
D)  the net synthesis of long-chain fatty acids from citric acid cycle intermediates. 
E)  both the net conversion of lipid to carbohydrate and the net synthesis of four-carbon dicarboxylic acids from acetyl-CoA. 
A)  the complete oxidation of acetyl-CoA to CO2 plus reduced coenzymes. 
B)  the net conversion of lipid to carbohydrate. 
C)  the net synthesis of four-carbon dicarboxylic acids from acetyl-CoA. 
D)  the net synthesis of long-chain fatty acids from citric acid cycle intermediates. 
E)  both the net conversion of lipid to carbohydrate and the net synthesis of four-carbon dicarboxylic acids from acetyl-CoA.

Question 19

Which citric acid cycle intermediate is chiral?

Accepted Answer

A)  citrate 
B)  $\alpha$-ketoglutarate 
C)  fumarate 
D)  succinate 
E)  malate 
A)  citrate 
B)  $\alpha$-ketoglutarate 
C)  fumarate 
D)  succinate 
E)  malate

Question 20

Which factor is NOT associated with the oxidation of substrates by the citric acid cycle?

Accepted Answer

A)  CO2 production 
B)  flavin reduction 
C)  the presence of lipoic acid in some of the enzyme systems 
D)  pyridine nucleotide oxidation 
E)  All of these factors are associated with the oxidation of substrates by the citric acid cycle. 
A)  CO2 production 
B)  flavin reduction 
C)  the presence of lipoic acid in some of the enzyme systems 
D)  pyridine nucleotide oxidation 
E)  All of these factors are associated with the oxidation of substrates by the citric acid cycle.

Exam 16: The Citric Acid Cycle

Which enzyme class is NOT found in the citric acid cycle?

Briefly describe the relationship of the pyruvate dehydrogenase complex reaction to glycolysis and the citric acid cycle.

How many ATP equivalents are made from the aerobic conversion of pyruvate to oxaloacetate?

Which three of the choices listed are possible sources for acetyl-CoA that enters the citric acid cycle? 1. oxidative decarboxylation of pyruvate 2. β oxidation of fatty acids 3. catabolism of certain amino acids 4. citrate 5. carboxylation of pyruvate

The pyruvate dehydrogenase complex catalyzes the oxidative decarboxylation of pyruvate. Two of the steps catalyzed by this complex do not involve any of the carbons of pyruvate. Briefly describe these reaction steps.

Show the steps of the citric acid cycle in which a six-carbon compound is converted into the first four-carbon intermediate in the path. For each step, show structures of substrate and product, name the enzyme responsible, and show where cofactors participate.

Which cofactors associated with the pyruvate dehydrogenase complex are classified as prosthetic groups? 1) TPP 2) lipoate 3) CoA-SH 4) NAD+ 5) FAD

Show the reactions by which α\alphaα -ketoglutarate is converted to malate in the citric acid cycle.

Show the steps of the citric acid cycle from succinyl-CoA to oxaloacetate only. For each step, show structures of substrate and product, name the enzyme responsible, and show where cofactors participate.

Which enzymes catalyze oxidation reactions in the citric acid cycle? 1) succinate dehydrogenase 2) pyruvate dehydrogenase 3) citrate dehydrogenase 4) α\alphaα -ketoglutarate dehydrogenase

During seed germination, the glyoxylate pathway is important to plants because it enables them to:

Citrate synthase and the NAD+-specific isocitrate dehydrogenase are two key regulatory enzymes of the citric acid cycle. These enzymes are inhibited by:

Which type of reaction is found in the citric acid cycle?

Intermediates in the citric acid cycle are used as precursors in the biosynthesis of:

What is the function of FAD in the pyruvate dehydrogenase complex? How is it regenerated?

Which reaction in the citric acid cycle will NOT proceed in the absence of inorganic phosphate ions?

Which cofactor is required for the conversion of fumarate to succinate?

A function of the glyoxylate cycle, in conjunction with the citric acid cycle, is to accomplish:

Which citric acid cycle intermediate is chiral?

Which factor is NOT associated with the oxidation of substrates by the citric acid cycle?

The Foundations of Biochemistry

Water

Amino Acids, Peptides, and Proteins

The Three-Dimensional Structure of Proteins

Protein Function

Enzymes

Carbohydrates and Glycobiology

Nucleotides and Nucleic Acids

DNA-Based Information Technologies

Lipids

Biological Membranes and Transport

Biosignaling

Bioenergetics and Biochemical Reaction Types

Glycolysis, Gluconeogenesis, and the Pentose Phosphate Pathway

Principles of Metabolic Regulation

Fatty Acid Catabolism

Amino Acid Oxidation and the Production of Urea

Oxidative Phosphorylation and Photophosphorylation

Carbohydrate Biosynthesis in Plants and Bacteria

Lipid Biosynthesis

Biosynthesis of Amino Acids, Nucleotides, and Related Molecules

Hormonal Regulation and Integration of Mammalian Metabolism

Genes and Chromosomes

DNA Metabolism

RNA Metabolism

Protein Metabolism

Regulation of Gene Expression

Filters

Which cofactors associated with the pyruvate dehydrogenase complex are classified as prosthetic groups? 1) TPP 2) lipoate 3) CoA-SH 4) NAD⁺ 5) FAD

Show the reactions by which $\alpha$ -ketoglutarate is converted to malate in the citric acid cycle.

Which enzymes catalyze oxidation reactions in the citric acid cycle? 1) succinate dehydrogenase 2) pyruvate dehydrogenase 3) citrate dehydrogenase 4) $\alpha$ -ketoglutarate dehydrogenase

Citrate synthase and the NAD⁺-specific isocitrate dehydrogenase are two key regulatory enzymes of the citric acid cycle. These enzymes are inhibited by: