Questions and Answers
What type of phosphorylation occurs during the conversion of phosphoenolpyruvate to pyruvate?
During glycolysis, how many ATP molecules are consumed in the energy investment phase?
Which enzyme catalyzes the dehydration of 2-phosphoglycerate?
What is the net gain of ATP from one round of glycolysis?
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What is the major fate of pyruvate in poorly vascularized tissues?
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Which enzyme catalyzes the conversion of phosphoenolpyruvate to pyruvate?
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What key role does the enzyme phosphoglycerate mutase play in glycolysis?
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Which statement about NADH in glycolysis is correct?
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What is the net gain of ATP molecules during the energy generation phase of glycolysis?
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What effect does glucose 6-phosphate have on hexokinase activity?
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Which hexokinase isozyme is primarily found in liver parenchymal cells and β cells of the pancreas?
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Which step of glycolysis involves the isomerization of glucose 6-phosphate to fructose 6-phosphate?
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What is the primary function of glucokinase in β cells of the pancreas?
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In most tissues, which enzyme catalyzes the phosphorylation of glucose?
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Which of the following statements about hexokinase is correct?
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What is the result of the phosphorylation of glucose during the energy investment phase?
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What is the primary regulatory enzyme in glycolysis that catalyzes the phosphorylation of fructose 6-phosphate?
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Which glycolysis step involves the cleavage of fructose 1,6-bisphosphate to form two triose phosphate molecules?
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What is produced as a result of the oxidation of glyceraldehyde 3-phosphate in glycolysis?
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Which enzyme catalyzes the conversion of 1,3-bisphosphoglycerate to 3-phosphoglycerate, resulting in the production of ATP?
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What must happen to dihydroxyacetone phosphate for it to continue through the glycolytic pathway?
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Which molecule serves as the primary source of energy for the synthesis of ATP from ADP in glycolysis?
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What is the overall net production of glyceraldehyde 3-phosphate from each glucose molecule during glycolysis?
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What key process occurs in glycolysis that involves a dehydrogenase enzyme and NAD+?
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Study Notes
Energy Generation Phase
- Glycolysis includes an energy generation phase where a net production of 2 ATP molecules occurs per glucose metabolized through substrate-level phosphorylation.
Energy Investment Phase
- Begins with the irreversible phosphorylation of glucose, trapping it as glucose 6-phosphate and committing it to metabolism.
Hexokinase
- Enzyme responsible for glucose phosphorylation in most tissues.
- Broad substrate specificity, phosphorylating multiple hexoses.
- Inhibited by glucose 6-phosphate, regulating its own activity.
- Low Km signifies high affinity for glucose, enabling efficient phosphorylation even at low glucose concentrations.
Glucokinase
- Predominantly found in liver and pancreatic β cells, serving as a glucose sensor for insulin secretion.
- Promotes glucose phosphorylation during hyperglycemic conditions.
- Similar substrate specificity to hexokinase despite the misleading name.
Stepwise Reactions in the Energy Investment Phase
- Isomerization: Glucose 6-phosphate converts to fructose 6-phosphate via phosphoglucose isomerase; the reaction is reversible and not rate-limiting.
- Phosphorylation of Fructose 6-Phosphate: Irreversible phosphorylation catalyzed by phosphofructokinase-1 (PFK-1), critical control point and rate-limiting step of glycolysis; regulated by ATP and fructose 6-phosphate levels.
- Cleavage of Fructose 1,6-bisphosphate: Aldolase cleaves this compound into dihydroxyacetone phosphate and glyceraldehyde 3-phosphate; the reaction is reversible.
- Isomerization of Dihydroxyacetone Phosphate: Dihydroxyacetone phosphate converts to glyceraldehyde 3-phosphate through triose phosphate isomerase, generating two molecules of glyceraldehyde 3-phosphate for further metabolism.
Energy Generating Phase
- Oxidation of Glyceraldehyde 3-Phosphate: Glyceraldehyde 3-phosphate transforms into 1,3-bisphosphoglycerate (1,3-BPG) via glyceraldehyde 3-phosphate dehydrogenase, producing NADH as it oxidizes the aldehyde end.
- Synthesis of 3-Phosphoglycerate: The conversion of 1,3-BPG to 3-phosphoglycerate occurs with ATP generation; catalyzed by phosphoglycerate kinase, this reaction is reversible. Each glucose yields two molecules of 1,3-BPG, compensating for prior ATP consumption.
Additional Steps
- Shift of Phosphate: Phosphate group shifts from carbon 3 to carbon 2 via phosphoglycerate mutase, a freely reversible reaction.
- Dehydration of 2-Phosphoglycerate: Enolase catalyzes the dehydration of 2-phosphoglycerate to phosphoenolpyruvate (PEP), a reversible reaction that redistributes energy.
- Formation of Pyruvate: PEP is converted to pyruvate by pyruvate kinase in an irreversible manner; this reaction favors ATP production and concludes glycolysis, producing 2 pyruvate molecules from the two glyceraldehyde 3-phosphate units.
Final Products
- Overall glycolysis results in a net gain of 2 ATP and 2 NADH molecules. NADH must be transported to mitochondria for ATP production through the electron transport chain.
- Pyruvate can be reduced to lactate by lactate dehydrogenase in anaerobic conditions, primarily occurring in poorly vascularized tissues, including the lens of the eye, kidney medulla, testes, leukocytes, and red blood cells.
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Description
Explore the energy generation phase of glycolysis, where a net of two ATP molecules are produced through substrate-level phosphorylation. This quiz covers key steps, including the irreversible phosphorylation of glucose and its implications for metabolism. Test your understanding of these essential processes in cellular energy production.
