Role of ATP, Glycolysis, and the Citric Acid Cycle in Cellular Metabolism, Exams of Chemistry

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CHEM210 BIOCHEMISTRY

Module 7

Final Assessment

Q & A

(Each Question denotes its format. All questions are answered)

1. Open-ended: Describe the role of ATP in cellular metabolism and detail the process by which it is generated during glycolysis. Answer: ATP acts as the primary energy currency in cells, transferring energy from catabolic to anabolic processes. During glycolysis, ATP is generated in the substrate-level phosphorylation steps catalyzed by phosphoglycerate kinase and pyruvate kinase.
2. Fill-in-the-blank: The enzyme _______ catalyzes the rate- limiting step of the citric acid cycle. Answer: Isocitrate dehydrogenase.
3. True/False: The electron transport chain is part of the glycolytic pathway. Answer: False. The electron transport chain is a series of complexes located in the mitochondrial membrane and is not part of glycolysis.
4. Multiple-choice: Which of the following is not a product of the citric acid cycle? A) CO B) NADH C) ATP D) Acetyl-CoA Answer: D) Acetyl-CoA. It is a reactant that enters the cycle, not a product.
5. Open-ended: Explain the significance of the citric acid cycle in cellular respiration. Answer: The citric acid cycle is central to cellular respiration as it oxidizes acetyl-CoA to CO2, and in the process, generates NADH and FADH2 which are essential for ATP production in the electron transport chain.

6. Fill-in-the-blank: In lipid oxidation, fatty acids are transported into the mitochondria by _______. Answer: Carnitine.
7. True/False: Glycolysis can occur in the absence of oxygen. Answer: True. Glycolysis is an anaerobic process and does not require oxygen.
8. Multiple-choice: Which enzyme is not involved in the glycolytic pathway? A) Hexokinase B) Citrate synthase C) Phosphofructokinase D) Aldolase Answer: B) Citrate synthase. It is involved in the citric acid cycle.
9. Open-ended: Discuss the role of oxygen in the electron transport chain. Answer: Oxygen serves as the final electron acceptor in the electron transport chain, forming water and allowing for the maintenance of the proton gradient essential for ATP synthesis.
10. Fill-in-the-blank: The conversion of 1,3-bisphosphoglycerate to 3-phosphoglycerate generates one molecule of _______. Answer: ATP.
11. True/False: The citric acid cycle occurs in the cytoplasm. Answer: False. The citric acid cycle takes place in the mitochondrial matrix.
12. Multiple-choice: Which of the following is not a fate of pyruvate in cellular metabolism?

A) Conversion to acetyl-CoA B) Lactate production C) Gluconeogenesis D) Direct incorporation into the electron transport chain Answer: D) Direct incorporation into the electron transport chain.

13. Open-ended: Describe the process and significance of the malate-aspartate shuttle. Answer: The malate-aspartate shuttle is crucial for transferring electrons from NADH produced in glycolysis across the mitochondrial membrane, as NADH cannot cross directly.
14. Fill-in-the-blank: The enzyme _______ is inhibited by ATP and activated by ADP, acting as a metabolic regulator. Answer: Phosphofructokinase.
15. True/False: Beta-oxidation of fatty acids generates acetyl-CoA that can enter the citric acid cycle. Answer: True. Beta-oxidation breaks down fatty acids to produce acetyl-CoA, which can then be oxidized in the citric acid cycle for energy production. Fill in the blank: In glycolysis, glucose is converted to two molecules of pyruvate. Rationale: Glycolysis is the initial step in cellular respiration and involves the breakdown of glucose into simpler compounds. True or False: The citric acid cycle takes place in the cytoplasm of the cell. Answer: False Rationale: The citric acid cycle, also known as the Krebs cycle, occurs in the mitochondria of eukaryotic cells.

Multiple Choice: Which enzyme catalyzes the conversion of citrate to isocitrate in the citric acid cycle? A) Citrate synthase B) Aconitase C) Isocitrate dehydrogenase D) Succinyl-CoA synthetase Answer: C) Isocitrate dehydrogenase Rationale: Isocitrate dehydrogenase is responsible for the conversion of citrate to isocitrate in the citric acid cycle. Fill in the blank: The final electron acceptor in oxidative phosphorylation is oxygen. Rationale: Oxygen serves as the terminal electron acceptor in the electron transport chain, playing a crucial role in ATP synthesis. True or False: Lipid oxidation primarily occurs in the cytoplasm of cells. Answer: False Rationale: Lipid oxidation takes place in the mitochondria, where fatty acids are broken down to generate acetyl-CoA for energy production. Multiple Choice: Which enzyme is responsible for the rate- limiting step in glycolysis? A) Hexokinase B) Phosphofructokinase- 1 C) Pyruvate kinase D) Glucose- 6 - phosphatase Answer: B) Phosphofructokinase- 1 Rationale: Phosphofructokinase-1 catalyzes the conversion of fructose- 6 - phosphate to fructose-1,6-bisphosphate, a crucial

regulatory step in glycolysis. Fill in the blank: The breakdown of one molecule of glucose in glycolysis generates a net gain of two molecules of ATP. Rationale: ATP is produced through substrate-level phosphorylation during glycolysis, yielding a net gain of two ATP molecules per glucose molecule. True or False: The citric acid cycle is a linear pathway that operates independently of other metabolic processes. Answer: False Rationale: The citric acid cycle is interconnected with other metabolic pathways, such as glycolysis and fatty acid oxidation, through shared intermediates. Multiple Choice: Which molecule allosterically activates pyruvate carboxylase, a key enzyme in gluconeogenesis? A) Acetyl-CoA B) ATP C) Fructose-1,6-bisphosphate D) NADH Answer: A) Acetyl-CoA Rationale: Acetyl-CoA serves as an allosteric activator of pyruvate carboxylase, promoting the conversion of pyruvate to oxaloacetate in gluconeogenesis. Fill in the blank: The citric acid cycle produces three molecules of NADH and one molecule of FADH2 per cycle. Rationale: NADH and FADH2 generated in the citric acid cycle play crucial roles in electron transport chain and ATP synthesis. True or False: The conversion of acetyl-CoA to citrate is an

irreversible step in the citric acid cycle. Answer: True Rationale: Citrate synthase catalyzes the condensation of acetyl-CoA and oxaloacetate to form citrate, which is a thermodynamically favorable and irreversible reaction. Multiple Choice: Which enzyme is responsible for the conversion of succinyl-CoA to succinate in the citric acid cycle? A) Citrate synthase B) Aconitase C) Succinyl-CoA synthetase D) Succinate dehydrogenase Answer: D) Succinate dehydrogenase Rationale: Succinate dehydrogenase catalyzes the oxidation of succinate to fumarate while reducing FAD to FADH2 in the citric acid cycle. Fill in the blank: Lipid oxidation produces a high yield of ATP compared to carbohydrate metabolism. Rationale: Fatty acids are a dense energy source, and their oxidation yields more ATP per carbon atom compared to glucose metabolism. True or False: The beta-oxidation of fatty acids occurs in the mitochondria. Answer: True Rationale: Beta-oxidation takes place in the mitochondrial matrix, where fatty acids are sequentially broken down into acetyl-CoA molecules. Multiple Choice: Which of the following is a ketone body produced during fatty acid oxidation? A) Acetoacetate

B) Malonyl-CoA C) Isocitrate D) Glyceraldehyde- 3 - phosphate Answer: A) Acetoacetate Rationale: Acetoacetate is one of the ketone bodies generated during fatty acid oxidation under conditions of high energy demand or low carbohydrate availability.

1. Fill in the blank: In glycolysis, glucose is converted to ___________. Answer: pyruvate Rationale: Glycolysis is the process in which glucose is broken down into pyruvate, generating ATP and NADH.
2. True or false: The citric acid cycle takes place in the cytoplasm of the cell. Answer: False Rationale: The citric acid cycle, also known as the Krebs cycle, takes place in the mitochondria of the cell.
3. Which of the following is NOT a product of glycolysis? a) ATP b) NADH c) FADH d) Pyruvate Answer: c) FADH Rationale: FADH2 is produced in the citric acid cycle, not glycolysis.
4. Fill in the blank: The end product of the citric acid cycle is ___________. Answer: ATP, NADH, FADH

Rationale: The citric acid cycle generates ATP, NADH, and FADH2, which are important molecules for the electron transport chain.

5. True or false: Lipid oxidation primarily occurs in the cytoplasm of the cell. Answer: False Rationale: Lipid oxidation primarily occurs in the mitochondria, where fatty acids are broken down to generate ATP.
6. Which of the following is NOT a step in glycolysis? a) Phosphofructokinase b) Pyruvate dehydrogenase c) Hexokinase d) Aldolase Answer: b) Pyruvate dehydrogenase Rationale: Pyruvate dehydrogenase is involved in the conversion of pyruvate to acetyl-CoA, not glycolysis.
7. Fill in the blank: The primary function of the citric acid cycle is to _______. Answer: generate high-energy electron carriers (NADH and FADH2) Rationale: The citric acid cycle is a central metabolic pathway that generates high-energy electron carriers for the electron transport chain.
8. True or false: The electron transport chain is located in the outer membrane of the mitochondria. Answer: False Rationale: The electron transport chain is located in the inner membrane of the mitochondria.

9. Which of the following molecules is NOT involved in the oxidation of fatty acids? a) Acetyl-CoA b) NADPH c) FADH d) Coenzyme A Answer: b) NADPH Rationale: NADPH is a molecule involved in biosynthesis, not fatty acid oxidation.
10. Fill in the blank: The total ATP yield from the citric acid cycle and glycolysis is ________. Answer: 38 ATP Rationale: The combined ATP yield from glycolysis, the citric acid cycle, and oxidative phosphorylation is 38 ATP.
11. True or false: Glycolysis can occur in the absence of oxygen. Answer: True Rationale: Glycolysis is an anaerobic process that can occur in the absence of oxygen.
12. Which of the following enzymes is NOT involved in the citric acid cycle? a) Isocitrate dehydrogenase b) Phosphofructokinase c) Citrate synthase d) Succinate dehydrogenase Answer: b) Phosphofructokinase Rationale: Phosphofructokinase is an enzyme in glycolysis, not the citric acid cycle.
13. Fill in the blank: Lipid oxidation involves the breakdown of ________ into acetyl-CoA.

Answer: fatty acids Rationale: Lipid oxidation is the process in which fatty acids are broken down into acetyl-CoA to generate ATP.

14. True or false: The citric acid cycle is regulated by feedback inhibition from high concentrations of ATP. Answer: True Rationale: High levels of ATP can inhibit key enzymes in the citric acid cycle to regulate energy production.
15. Which of the following is NOT a key intermediate in glycolysis? a) Pyruvate b) Fructose 1,6-bisphosphate c) Acetyl-CoA d) 3-phosphoglycerate Answer: c) Acetyl-CoA Rationale: Acetyl-CoA is a key intermediate in the citric acid cycle, not glycolysis.
16. Fill in the blank: The final electron acceptor in the electron transport chain is ________. Answer: oxygen Rationale: Oxygen is the final electron acceptor in the electron transport chain, which forms water when combined with electrons and protons.
17. True or false: The citric acid cycle is an aerobic pathway. Answer: True Rationale: The citric acid cycle requires oxygen to function and is considered an aerobic pathway.
18. Which of the following is NOT a product of the electron

transport chain? a) ATP b) NAD+ c) FAD d) Water Answer: b) NAD+ Rationale: NAD+ is a coenzyme that is regenerated during the electron transport chain, not a product of it.

19. Fill in the blank: In the presence of oxygen, pyruvate is converted to ________ in the mitochondria. Answer: acetyl-CoA Rationale: Pyruvate is converted to acetyl-CoA in the mitochondria before entering the citric acid cycle.
20. True or false: Lipid oxidation generates more ATP per gram than glycolysis. Answer: True Rationale: Fatty acids are a more efficient energy source compared to glucose, generating more ATP per gram through lipid oxidation.
21. Which of the following enzymes is NOT involved in glycolysis? a) Hexokinase b) Phosphofructokinase c) Citrate synthase d) Pyruvate kinase Answer: c) Citrate synthase Rationale: Citrate synthase is an enzyme in the citric acid cycle, not glycolysis.
22. Fill in the blank: The ___________ shuttle transfers electrons

from NADH produced in the cytoplasm into the mitochondria. Answer: malate-aspartate Rationale: The malate-aspartate shuttle is a mechanism that transfers electrons from NADH in the cytoplasm into the mitochondria for oxidative phosphorylation.

23. True or false: The conversion of pyruvate to acetyl-CoA is an irreversible step in glycolysis. Answer: True Rationale: The conversion of pyruvate to acetyl-CoA by pyruvate dehydrogenase is an irreversible step in glycolysis, leading into the citric acid cycle.
24. Which of the following is NOT a function of the citric acid cycle? a) Generation of ATP b) Generation of NADH and FADH c) Production of amino acids d) Regeneration of oxaloacetate Answer: c) Production of amino acids Rationale: The citric acid cycle is primarily involved in generating high-energy electron carriers and ATP, as well as regenerating oxaloacetate.
25. Fill in the blank: The citric acid cycle is also known as the ________ cycle. Answer: Krebs Rationale: The citric acid cycle is named after Hans Krebs, who discovered the series of chemical reactions involved in the pathway.
26. True or false: Lipid oxidation primarily occurs during times of high carbohydrate intake.

Answer: False Rationale: Lipid oxidation is a process that primarily occurs when the body requires additional energy and is not dependent on carbohydrate intake.

27. Which of the following molecules is a key player in the allosteric regulation of glycolysis? a) Insulin b) ATP c) Glucagon d) Pyruvate Answer: b) ATP Rationale: ATP acts as a negative regulator of glycolysis, inhibiting key enzymes such as phosphofructokinase when cellular energy levels are high.
28. Fill in the blank: The electron transport chain generates a proton gradient across the ________ membrane of the mitochondria. Answer: inner Rationale: The electron transport chain pumps protons across the inner mitochondrial membrane, creating a gradient that drives ATP synthesis.
29. True or false: The citric acid cycle is a linear pathway that does not contain any branching reactions. Answer: False Rationale: The citric acid cycle contains several branching reactions that lead to the generation of key intermediates for energy production.
30. Which of the following is NOT a product of lipid oxidation? a) Acetyl-CoA

b) NADH c) FADH d) Pyruvate Answer: d) Pyruvate Rationale: Pyruvate is a product of glycolysis, not lipid oxidation.