Questions and Answers
Which enzyme is primarily associated with the regulation of glycolysis as the rate-limiting step?
What effect does fasting have on glucokinase activity in tissues?
Which characteristics distinguish glucokinase from hexokinase?
Which of the following conditions leads to increased glucose oxidation via glucokinase?
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What role does pyruvate kinase play in the process of glycolysis?
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How does fatty acid oxidation affect glycolysis during fasting?
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Which enzyme is a significant indicator of inherited enzymopathies in red blood cells?
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How does glucagon affect hexokinase IV activity in the liver?
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Which statement is true regarding the Km value of hexokinase compared to glucokinase?
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In what manner does insulin influence glucokinase activity in the liver?
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Study Notes
Carbohydrate Metabolism
- Glycolysis: oxidation of glucose to pyruvic acid (aerobic) or lactic acid (anaerobic).
- Takes place in the cytosol of all cells, converting 1 mol of glucose (6C) into 2 moles of pyruvate or lactate (3C).
Fate of Dietary Sugars
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Glucose oxidation leads to:
- Major Pathway: Glycolysis → Krebs cycle → Electron Transport Chain (ETC)
- Minor Pathway: Hexose monophosphate (HMP) shunt and Uronic acid pathway.
- Storage: Glycogen formation, conversion into TAG (triacylglycerols).
Glycolysis Steps
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Phases of Glycolysis:
- Energy investment phase (first five reactions).
- Energy generation phase (remainder of reactions).
- Lactate production occurs in:
- Red Blood Cells (RBC) due to absence of mitochondria.
- Exercising muscles due to low oxygen availability.
Energy Investment and Generation
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Energy Investment:
- Initial phosphorylation of glucose traps it as glucose-6-phosphate (G6P).
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Energy Generation:
- In aerobic glycolysis:
- Glucokinase and Phosphofructokinase consume 2 ATP.
- Phosphoglycerate kinase and Pyruvate kinase generate 4 ATP.
- Total net gain: 7 ATP.
- In anaerobic glycolysis:
- Similar consumption of 2 ATP, but total net gain is only 2 ATP.
- In aerobic glycolysis:
Importance of Glycolysis
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Energy Production:
- Aerobic conditions yield 7 ATP; anaerobic conditions yield 2 ATP.
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In Erythrocytes:
- Sole source of ATP and production of 2,3-bisphosphoglycerate (2,3 BPG).
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Intermediates:
- Produce important compounds like TAG, glycerol-3-phosphate, and serine.
Clinical Applications of Glycolysis
- Glyceraldehyde-3-phosphate dehydrogenase: susceptible to arsenic and iodoacetate.
- Enolase: inhibited by fluoride via magnesium chelation, affecting glucose estimation.
- Pyruvate Kinase: 95% deficiency contributes to inherited enzymopathies in RBCs.
Regulation of Glycolysis
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Key enzymes include:
- Glucokinase (GK) or Hexokinase (HK).
- Phosphofructokinase (PFK-1): primary control point.
- Pyruvate kinase (PK).
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Allosteric Regulation:
- Hexokinase has low Km (high affinity); Glucokinase has high Km (low affinity).
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Hormonal Regulation:
- Insulin has no effect on GK, but induces HK.
- Glucagon represses HK activity while having no effect on GK.
Short-term and Long-term Regulation
- Short-term regulation involves phosphorylation/dephosphorylation.
- Long-term regulation includes enzyme synthesis.
Effect of Fatty Acid Oxidation
- Fatty acid oxidation decreases the rate of glycolysis during fasting or carbohydrate deprivation, reserving glucose for the brain.
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Description
Test your understanding of carbohydrate metabolism, focusing on glycolysis and the fate of dietary sugars. This quiz covers pathways such as the Krebs cycle, oxidative processes, and the storage forms of glucose. Prepare to explore the major and minor pathways of glucose oxidation.
