Glycolysis Quiz

Glycolysis

• Breakdown of glucose into pyruvate
• Main function: energy production in the form of ATP
• Occurs in the cytosol of all tissues
• All sugars can be converted to glucose and metabolized by glycolysis

Key Steps of Glycolysis

• Glucose-6-phosphate formed from glucose, catalyzed by glucokinase or hexokinase
• Fructose-6-phosphate formed from glucose-6-phosphate, catalyzed by phosphohexose isomerase
• Fructose-1,6-bisphosphate formed from Fructose-6-phosphate, catalyzed by phosphofructokinase (PFK) (rate-limiting enzyme)
• Glyceraldehyde-3-phosphate and Dihydroxyacetone phosphate (DHA-P) formed from Fructose-1,6-bisphosphate, catalyzed by aldolase A
• 1,3-Bisphosphoglycerate formed from Glyceraldehyde-3-phosphate, catalyzed by glyceraldehyde-3-phosphate dehydrogenase, generating NADH
• 3-Phosphoglycerate formed from 1,3-Bisphosphoglycerate, catalyzed by phosphoglycerate kinase, generating ATP (substrate-level phosphorylation)
• 2-Phosphoglycerate formed from 3-Phosphoglycerate, catalyzed by phosphoglycerate mutase
• Phosphoenolpyruvate (PEP) formed from 2-Phosphoglycerate, catalyzed by enolase
• Pyruvate formed from PEP, catalyzed by pyruvate kinase, generating ATP (substrate-level phosphorylation)

End Products of Glycolysis

• Aerobic Glycolysis: Occurs in cells with mitochondria and adequate oxygen supply. Generates 2 pyruvate, 2 NADH.
  • Pyruvate enters the mitochondria and is converted to acetyl CoA, which enters the citric acid cycle for further ATP production
  • NADH utilizes mitochondria and oxygen to yield additional energy
• Anaerobic Glycolysis: Occurs in cells without mitochondria or adequate oxygen supply. Generates 2 lactate.
  • Lactate formed from pyruvate by utilizing NADH

Energy Yield from Glycolysis

• Anaerobic Glycolysis: Net yield of 2 ATP per glucose molecule. Important for tissues with limited oxygen supply (e.g. skeletal muscles during intense exercise), and tissues without mitochondria (e.g. red blood cells)
• Aerobic Glycolysis: Net yield of 8 ATP per glucose molecule, plus 2 NADH.
  • 2 NADH produce 6 ATP when entering the electron transport chain in mitochondria. Total aerobic glycolysis yield is 2 + 6 = 8 ATP.
• Complete aerobic oxidation of glucose: 2 pyruvate converted to 2 acetyl CoA, generating 6 ATP.
  • 2 acetyl CoA entering the citric acid cycle produce 24 ATP. Total yield from complete aerobic oxidation is 38 ATP per glucose molecule.

Regulation of Glycolysis

• Short-term regulation: Enzyme activity is influenced by substrate availability, product inhibition, and allosteric effectors.
• Long-term regulation: Synthesis and degradation of glycolytic enzymes are influenced by hormones like insulin (induction) and glucagon (repression).

Key Enzymes in Glycolysis

• Glucokinase (liver) and Hexokinase (other tissues): regulate glucose entry into glycolysis
• Phosphofructokinase (PFK): rate-limiting enzyme of glycolysis, regulated by allosteric effectors (ATP, AMP, citrate, fructose-2,6-bisphosphate)
• Pyruvate kinase: catalyzes the final step of glycolysis, regulated by phosphorylation (insulin and glucagon)

Genetic Defects of Glycolytic Enzymes

• Pyruvate kinase deficiency: Reduces glycolysis rate and ATP production, leading to hemolytic anemia due to impaired red blood cell function.