Chpt 3 Anaerobic Metabolism

Question 1

1. Question: Which of the following is NOT a major source of energy for cells? Options: a) Carbohydrates b) Lipids c) Proteins d) Vitamins

Answer 1

Answer: d) Vitamins Explanation: Vitamins are essential organic compounds but they are not a major source of energy. Carbohydrates lipids and proteins are all macronutrients that can be broken down to produce ATP the cell’s primary energy currency.

Question 2

2. Question: Approximately what percentage of energy from glucose is released during glycolysis? Options: a) 7% b) 10% c) 50% d) 93%

Answer 2

Answer: a) 7% Explanation: Glycolysis only extracts a small portion of the total energy stored in glucose. The majority of energy is released during oxidative phosphorylation (in aerobic respiration).

Question 3

3. Question: Where in the cell do anaerobic processes like glycolysis and fermentation take place? Options: a) Nucleus b) Mitochondria c) Cytoplasm d) Golgi apparatus

Answer 3

Answer: c) Cytoplasm Explanation: Glycolysis and fermentation are anaerobic processes that occur in the cytoplasm of the cell not requiring the mitochondria.

Question 4

4. Question: Which of the following is NOT an activated carrier involved in anaerobic metabolism? Options: a) ATP b) NADH c) Acetyl CoA d) FADH2

Answer 4

Answer: c) Acetyl CoAExplanation: Acetyl CoA is an activated carrier involved in aerobic respiration (specifically the citric acid cycle) not anaerobic metabolism. ATP and NADH are crucial in both aerobic and anaerobic processes while FADH2 plays a role in aerobic respiration.

Question 5

5. Question: What is the ultimate electron acceptor in aerobic respiration? Options: a) Water b) Carbon dioxide c) Oxygen d) Pyruvate

Answer 5

Answer: c) OxygenExplanation: In aerobic respiration oxygen acts as the final electron acceptor in the electron transport chain.

Question 6

6. Question: What is the main product of the first stage of cellular respiration? Options: a) Glucose b) Pyruvate c) Acetyl CoA d) ATP

Answer 6

Answer: b) PyruvateExplanation: The first stage of cellular respiration is glycolysis which produces pyruvate.

Question 7

7. Question: In which stage of cellular respiration is carbon dioxide (CO2) released? Options: a) First stage b) Second stage c) Third stage d) All stages

Answer 7

Answer: b) Second stageExplanation: Carbon dioxide is released during the citric acid cycle (the second stage of cellular respiration).

Question 8

8. Question: The glycolytic pathway is a series of how many reactions? Options: a) 5 b) 8 c) 10 d) 12

Answer 8

Answer: c) 10Explanation: The glycolytic pathway consists of ten enzyme-catalyzed reactions.

Question 9

9. Question: Who is credited with discovering the glycolytic pathway? Options: a) Hans Krebs b) Gustav Embden c) Otto Meyerhof d) Both b and c

Answer 9

Answer: d) Both b and c Explanation: Gustav Embden and Otto Meyerhof are both credited with significant contributions to the discovery and elucidation of the glycolytic pathway.

Question 10

10. Question: What are the two phases of glycolysis? Options: a) Preparatory and payoff b) Oxidation and reduction c) Anaerobic and aerobic d) Citric acid cycle and electron transport chain

Answer 10

Answer: a) Preparatory and payoffExplanation: Glycolysis is divided into two phases: the preparatory phase (energy investment) and the payoff phase (energy generation).

Question 11

11. Question: How many ATP molecules are used in the preparatory phase of glycolysis? Options: a) 0 b) 1 c) 2 d) 4

Answer 11

Answer: c) 2 Explanation: Two ATP molecules are consumed in the preparatory phase of glycolysis to phosphorylate glucose and fructose-6-phosphate.

Question 12

12. Question: How many ATP molecules are produced in the payoff phase of glycolysis? Options: a) 2 b) 4 c) 6 d) 8

Answer 12

Answer: b) 4 Explanation: Four ATP molecules are produced in the payoff phase of glycolysis through substrate-level phosphorylation.

Question 13

13. Question: What is the fate of pyruvate in the yeast cell under anaerobic conditions? Options: a) Lactic acid b) Ethanol c) Acetyl CoA d) Glucose

Answer 13

Answer: b) Ethanol Explanation: In yeast under anaerobic conditions pyruvate is converted to ethanol through alcoholic fermentation.

Question 14

14. Question: How many molecules of NADH are produced per glucose molecule during glycolysis? Options: a) 1 b) 2 c) 3 d) 4

Answer 14

Answer: b) 2 Explanation: Two molecules of NADH are produced per glucose molecule during glycolysis (one per glyceraldehyde-3-phosphate molecule).

Question 15

15. Question: Which enzyme catalyzes the conversion of pyruvate to acetyl-CoA? Options: a) Hexokinase b) Phosphofructokinase c) Pyruvate dehydrogenase d) Lactate dehydrogenase

Answer 15

Answer: c) Pyruvate dehydrogenase Explanation: Pyruvate dehydrogenase is the enzyme complex that catalyzes the conversion of pyruvate to acetyl-CoA in the link reaction before the citric acid cycle.

Question 16

16. Question: What are the two types of fermentation discussed in the text? Options: a) Alcoholic and lactic acid b) Aerobic and anaerobic c) Homolactic and heterolactic d) Ethanol and lactate

Answer 16

Answer: a) Alcoholic and lactic acid Explanation: These are the two main types of fermentation discussed in relation to anaerobic metabolism.

Question 17

17. Question: What is the product of alcoholic fermentation? Options: a) Lactate b) Ethanol and CO2 c) Acetyl CoA d) Glucose

Answer 17

Answer: b) Ethanol and CO2 Explanation: Alcoholic fermentation produces ethanol and carbon dioxide as byproducts.

Question 18

18. Question: Which coenzyme is required for the decarboxylation of pyruvate to acetaldehyde in alcoholic fermentation? Options: a) NADH b) FADH2 c) Thiamine pyrophosphate d) Coenzyme A

Answer 18

Answer: c) Thiamine pyrophosphate Explanation: Thiamine pyrophosphate (TPP) is a coenzyme required by pyruvate decarboxylase for the decarboxylation of pyruvate.

Question 19

19. Question: What is regenerated in the second reaction of alcoholic fermentation? Options: a) Pyruvate b) Acetaldehyde c) Ethanol d) NAD+

Answer 19

Answer: d) NAD+ Explanation: The second reaction of alcoholic fermentation (aldehyde reductase) regenerates NAD+ from NADH allowing glycolysis to continue.

Question 20

20. Question: Where does homolactic fermentation occur? Options: a) Yeast cells b) Lactic acid bacteria and skeletal muscle c) Mitochondria d) Cytoplasm of all cells

Answer 20

Answer: b) Lactic acid bacteria and skeletal muscle Explanation: Homolactic fermentation occurs in lactic acid bacteria and also in vertebrate skeletal muscle cells during strenuous exercise.

Question 21

21. Question: What is the product of homolactic fermentation? Options: a) Ethanol b) Lactate c) Acetyl CoA d) CO2

Answer 21

Answer: b) Lactate Explanation: Homolactic fermentation produces only lactate as a product.

Question 22

22. Question: What is the standard free energy change (ΔG°’) for lactic acid fermentation? Options: a) +25.1 kJ/mol b) -25.1 kJ/mol c) 0 kJ/mol d) +3.5 kJ/mol

Answer 22

Answer: b) -25.1 kJ/mol Explanation: Lactic acid fermentation is an exergonic process with a negative standard free energy change.

Question 23

23. Question: Where is the NADH produced in homolactic fermentation useful? Options: a) Glycolysis b) Oxidative phosphorylation in the mitochondrial electron transport chain c) Citric acid cycle d) Gluconeogenesis

Answer 23

Answer: a) Glycolysis Explanation: In homolactic fermentation the NADH produced in glycolysis is used to reduce pyruvate to lactate regenerating NAD+ for continued glycolysis.

Question 24

24. Question: Which of the following reactions in glycolysis are irreversible? Options: a) All reactions b) Some reactions c) None of the reactions d) Only the reactions in the payoff phase

Answer 24

Answer: b) Some reactionsExplanation: The reactions catalyzed by hexokinase phosphofructokinase-1 and pyruvate kinase are irreversible under standard cellular conditions.

Question 25

25. Question: Why is NAD+ regeneration important in anaerobic conditions? Options: a) To produce ATP b) To allow glycolysis to continue c) To form lactic acid d) To activate pyruvate dehydrogenase

Answer 25

Answer: b) To allow glycolysis to continue Explanation: NAD+ is a required coenzyme for glycolysis. Its regeneration is essential for the continued oxidation of glyceraldehyde-3-phosphate. Without NAD+ regeneration glycolysis would halt.

Question 26

1 Explain the role of activated carriers like ATP NADH and acetyl CoA in anaerobic metabolism. What are their functions and how are they produced and consumed during these processes

Answer 26

Answer: In anaerobic metabolism the roles of activated carriers are somewhat limited compared to aerobic respiration. Acetyl-CoA is not directly involved in anaerobic metabolism as it’s a key player in the aerobic citric acid cycle • ATP: Functions as the primary energy currency. It’s produced through substrate-level phosphorylation (direct transfer of a phosphate group from a high-energy molecule to ADP) during glycolysis. It’s consumed in the early steps of glycolysis (hexokinase and phosphofructokinase) to phosphorylate glucose and fructose-6-phosphate • NADH: Functions as an electron carrier. It’s produced during the oxidation of glyceraldehyde-3-phosphate in glycolysis. Under anaerobic conditions it is not used in an electron transport chain. Instead its electrons are used to reduce pyruvate to lactate (in lactic acid fermentation) or acetaldehyde to ethanol (in alcoholic fermentation) regenerating NAD+ which is crucial for glycolysis to continue

Question 27

2 Compare and contrast the two phases of glycolysis: the preparatory phase and the payoff phase. Describe the key reactions in each phase the net energy yield and the overall significance of these phases in anaerobic metabolism

Answer 27

Answer: Preparatory Phase (Energy Investment): • Key Reactions: Phosphorylation of glucose (hexokinase) isomerization of glucose-6-phosphate to fructose-6-phosphate (phosphoglucose isomerase) phosphorylation of fructose-6-phosphate to fructose-1 6-bisphosphate (phosphofructokinase-1) cleavage of fructose-1 6-bisphosphate into glyceraldehyde-3-phosphate and dihydroxyacetone phosphate (aldolase) isomerization of dihydroxyacetone phosphate to glyceraldehyde-3-phosphate (triose phosphate isomerase) • Net Energy Yield: A net consumption of 2 ATP • Significance: Prepares the glucose molecule for cleavage into two 3-carbon molecules setting the stage for energy generation in the payoff phase Payoff Phase (Energy Generation): • Key Reactions: Oxidation and phosphorylation of glyceraldehyde-3-phosphate to 1 3-bisphosphoglycerate (glyceraldehyde-3-phosphate dehydrogenase) substrate-level phosphorylation yielding ATP from 1 3-bisphosphoglycerate (phosphoglycerate kinase) isomerization of 3-phosphoglycerate to 2-phosphoglycerate (phosphoglyceromutase) dehydration of 2-phosphoglycerate to phosphoenolpyruvate (enolase) substrate-level phosphorylation yielding ATP from phosphoenolpyruvate (pyruvate kinase) • Net Energy Yield: Production of 4 ATP and 2 NADH • Significance: Generates ATP and NADH from the breakdown products of glucose. The ATP provides energy for cellular processes while the NADH is crucial for regeneration in fermentation Overall: While the preparatory phase consumes ATP the payoff phase generates a net gain of 2 ATP (4 produced - 2 consumed) and 2 NADH per glucose molecule in anaerobic glycolysis

Question 28

3 Discuss the fate of pyruvate under anaerobic conditions. Explain the two types of fermentation: alcoholic fermentation and homolactic fermentation. What are the final products the key enzymes involved and the locations where these processes typically occur

Answer 28

Answer: Under anaerobic conditions pyruvate cannot enter the citric acid cycle (requires oxygen). Instead it undergoes fermentation to regenerate NAD+ for glycolysis to continue Alcoholic Fermentation: • Final Products: Ethanol and carbon dioxide (CO2) • Key Enzymes: Pyruvate decarboxylase (removes CO2) alcohol dehydrogenase (reduces acetaldehyde to ethanol using NADH) • Location: Primarily occurs in yeast and some bacteria Homolactic Fermentation: • Final Products: Lactic acid • Key Enzymes: Lactate dehydrogenase (reduces pyruvate to lactate using NADH) • Location: Occurs in many bacteria (lactic acid bacteria) muscle cells under anaerobic conditions (e.g. during strenuous exercise)

Question 29

4 What is the significance of NAD+ regeneration during anaerobic metabolism How is NAD+ regenerated in alcoholic and homolactic fermentation Why is this process crucial for the continuation of glycolysis

Answer 29

Answer: NAD+ is a crucial coenzyme in glycolysis specifically in the glyceraldehyde-3-phosphate dehydrogenase reaction. Without sufficient NAD+ this step cannot occur halting glycolysis and ATP production • Alcoholic Fermentation: NADH reduces acetaldehyde to ethanol regenerating NAD+ • Homolactic Fermentation: NADH reduces pyruvate to lactate regenerating NAD+ Regeneration of NAD+ is essential because it allows glycolysis to continue producing ATP even in the absence of oxygen

Question 30

5 Glycolysis is often described as an ancient metabolic pathway. What evidence supports this view and what insights does this provide about the evolution of energy metabolism

Answer 30

Answer: Several lines of evidence support the ancient nature of glycolysis • Ubiquity: Glycolysis is found in nearly all living organisms from bacteria to humans suggesting its early emergence in evolutionary history • Simplicity: The pathway is relatively simple compared to other metabolic pathways suggesting it may have evolved before more complex processes • Anaerobic Nature: Its anaerobic nature indicates it could function before the evolution of oxygen-dependent respiration • Cytoplasmic Location: The reactions take place in the cytoplasm which is a primitive cellular compartment These observations suggest that glycolysis was a crucial early energy-generating pathway. More complex energy-generating processes like aerobic respiration likely evolved later building upon the foundation established by glycolysis. The existence of glycolysis highlights the fundamental importance of glucose metabolism for life’s evolution