Questions and Answers
During anaerobic glycolysis, how many molecules of ATP are synthesized by substrate level phosphorylation?
What is the net yield of ATP during anaerobic glycolysis?
How many ATP molecules are generated by the mitochondrial electron transport chain from 2 NADH molecules?
What is the net gain of energy from the glycolysis pathway when oxygen is available?
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What is the condition necessary for glucokinase to act?
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Which enzyme is activated by insulin?
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What is the role of ATP in the glycolysis pathway?
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What is the role of fructose-2,6-bisphosphate in the glycolysis pathway?
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What is the function of glucokinase in the liver?
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Which enzyme has a low Km and high affinity for glucose?
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What is the effect of insulin on pyruvate kinase?
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What is the product of pyruvate's oxidative decarboxylation?
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What is the effect of glucagon on glycolysis?
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What is the effect of high energy levels in the cell on glycolysis?
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Study Notes
Energy Yield from Glycolysis
- In anaerobic conditions, 1 glucose molecule converts to 2 lactate molecules, producing a net yield of 2 ATP molecules.
- 4 ATP molecules are synthesized through substrate-level phosphorylations, but 2 ATP molecules are used in steps 1 and 3, resulting in a net yield of 2 ATP molecules.
- The overall reaction is: Glucose + 2 Pi + 2 ADP → 2 Lactate + 2 ATP.
Aerobic Conditions
- In the presence of oxygen, the 2 NADH molecules generated in step 5 can enter the mitochondrial electron transport chain, producing 5 ATP molecules (2.5 ATP per NADH).
- The net energy gain from glycolysis in aerobic conditions is 7 ATP molecules.
Regulation of Glycolysis
- Key enzymes regulating glycolysis are: glucokinase/hexokinase (step 1), phosphofructokinase (step 3), and pyruvate kinase (step 9).
- Glucokinase/hexokinase is regulated by feedback inhibition (hexokinase by glucose-6-phosphate) and activated by insulin.
- Glucokinase is active mainly in the liver and has a high Km for glucose and low affinity, while hexokinase has a low Km and high affinity, making it suitable for phosphorylating glucose at lower concentrations.
- Phosphofructokinase (PFK) is the most important rate-limiting enzyme for glycolysis and is inhibited by ATP and citrate, while activated by AMP.
- Fructose-2,6-bisphosphate (F-2,6-BP) increases the activity of phospho-fructo kinase, which is formed from fructose-6-phosphate by PFK-2.
- Pyruvate kinase is a regulatory enzyme that catalyzes an irreversible step and is inhibited when energy is plentiful in the cell.
- Insulin activates pyruvate kinase, while glucagon inhibits it.
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Description
Calculate the net ATP yield from glucose in anaerobic and aerobic conditions, including the role of NADH and oxygen.
