Questions and Answers
What product is formed from 1,3-bisphosphoglycerate in RBCs during glycogenesis?
Which enzyme hydrolyzes 2,3-bisphosphoglycerate in RBCs?
What is the main product of the isomerization of dihydroxyacetone phosphate?
What is the effect of 2,3-bisphosphoglycerate on hemoglobin?
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Which enzyme is primarily affected by pyruvate kinase deficiency in terms of energy production?
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Which enzyme is responsible for the conversion of glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate?
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What role does hexokinase play in glycolysis regulation?
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What role does NAD+ play in the reaction converting glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate?
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How is glucokinase indirectly regulated in glycolysis?
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In substrate level phosphorylation, what compound provides the energy to synthesize ATP?
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What is the consequence of fluoride's presence in glycolysis?
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What is the consequence of pyruvate kinase deficiency in RBCs?
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How does 3-phosphoglycerate convert to 2-phosphoglycerate?
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Which of the following enzymes is activated by fructose 1,6-bisphosphate?
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What type of reaction is catalyzed by pyruvate kinase?
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Which molecule is produced alongside ATP during the conversion of phosphoenol pyruvate to pyruvate?
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Which enzyme is responsible for the phosphorylation of glucose to glucose 6-phosphate?
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What is the primary function of isomerization in glycolysis?
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Which reaction in glycolysis is catalyzed by phosphofructokinase and is considered the key regulatory step?
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Which molecule is produced during the breakdown of fructose 1,6-bisphosphate?
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In which phase of glycolysis does the phosphorylation of fructose 6-phosphate occur?
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What is the result of substrate-level phosphorylation during glycolysis?
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What effect does the phosphorylation of glucose have on its transport across the cell membrane?
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Which of the following tissues primarily relies on glycolysis for energy due to a lower presence of mitochondria?
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Study Notes
Isomerization
- Dihydroxyacetone phosphate is converted to glyceraldehyde 3-phosphate by phosphotriose isomerase.
- Two molecules of glyceraldehyde 3-phosphate are produced in this reversible reaction.
Oxidation
- Glyceraldehyde 3-phosphate undergoes dehydrogenation and phosphorylation to form 1,3-bisphosphoglycerate (1,3-BPG), catalyzed by glyceraldehyde 3-phosphate dehydrogenase (G3-P DH).
- NAD+ carries reducing equivalents, and the reaction is reversible.
- This step is critical for generating NADH + H+ and high-energy compound 1,3-BPG.
Substrate-Level Phosphorylation
- 1,3-BPG's energy is used to synthesize ATP and produce 3-phosphoglycerate via 3-phosphoglycerate kinase.
- This is an instance of substrate-level phosphorylation and is reversible.
- Arsenate inhibits this reaction.
Shift of Phosphoryl Group
- 3-phosphoglycerate is converted to 2-phosphoglycerate by phosphoglycerate mutase, involving a phosphate group shift from C3 to C2.
- This reaction is reversible.
Dehydration
- 2-phosphoglycerate is dehydrated to form phosphoenolpyruvate (PEP), a high-energy compound, catalyzed by enolase.
- This reversible reaction removes one water molecule and requires Mg++.
- Fluoride irreversibly inhibits enolase, halting glycolysis, which is why fluoride is used during blood sugar estimations.
Substrate-Level Phosphorylation
- PEP converts to pyruvate via pyruvate kinase, producing ATP through substrate-level phosphorylation.
- Pyruvate kinase is considered a key enzyme and this marks the third irreversible reaction in glycolysis.
2,3-Bisphosphoglycerate Shuttle
- In RBCs, 1,3-BPG is transformed into 2,3-bisphosphoglycerate (2,3-BPG) by bisphosphoglycerate mutase.
- 2,3-BPG is hydrolyzed to 3-phosphoglycerate by phosphatase, without generating ATP.
- 2,3-BPG lowers hemoglobin's oxygen affinity, facilitating oxygen delivery to tissues under hypoxia.
Pyruvate Kinase Deficiency
- This inherited disorder represents the most common enzyme defect in the glycolytic pathway.
- It results in reduced glycolysis rates in RBCs, causing an energy deficit and leading to hemolytic anemia due to the inability of RBCs to maintain their biconcave shape.
Regulation of Glycolysis
- Regulated through allosteric mechanisms, covalent modifications, and hormonal influences.
Allosteric Regulation
- Key glycolytic enzymes include hexokinase/glucokinase, phosphofructokinase, and pyruvate kinase.
- Hexokinase is inhibited by glucose 6-phosphate; glucokinase is inhibited by fructose-6-P and stimulated by glucose; pyruvate kinase is inhibited by high ATP and activated by fructose 1,6-bisphosphate.
Glycolysis Tissue Distribution
- Glycolysis is prominent in mature RBCs, contracting muscles (due to vessel occlusion), tissues with fewer mitochondria (kidney medulla, testicles, leukocytes), and in the brain and gastrointestinal tract.
Glycolysis Overview
- The glycolytic pathway breaks down glucose into two pyruvate molecules through a sequence of 10 reactions, divided into:
- Energy investment phase (Preparatory phase): first 5 steps
- Energy generation phase (Payoff phase): last 5 steps
Phosphorylation
- Glucose is activated by hexokinase or glucokinase to form glucose 6-phosphate, an irreversible reaction requiring ATP and Mg++.
- The impermeable glucose 6-phosphate traps glucose within the cell for energy production.
Isomerization
- Glucose 6-phosphate is isomerized to fructose 6-phosphate, undergoing a reversible rearrangement from aldose to ketose.
Second Phosphorylation
- Fructose 6-phosphate is phosphorylated to fructose 1,6-bisphosphate by phosphofructokinase (PFK), the key enzyme in glycolysis, using ATP.
- This reaction is the second irreversible step.
Breakdown of Fructose 1,6-bisphosphate
- The 6-carbon fructose 1,6-bisphosphate is split into two 3-carbon molecules: glyceraldehyde 3-phosphate and dihydroxyacetone phosphate, catalyzed by aldolase.
- This reaction is reversible.
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Description
Explore the biochemical processes of isomerization and oxidation involving glyceraldehyde 3-phosphate. This quiz covers key reactions catalyzed by phosphotriose isomerase and glyceraldehyde 3-phosphate dehydrogenase. Test your knowledge of reversible reactions in metabolic pathways.
