Glycolysis Lecture Notes

Introduction to Glycolysis

• Definition: Oxidizing glucose (6-carbon sugar) into pyruvate (3-carbon molecules).
• Source of Glucose: Derived from the diet, enters cells via transporters.

Glucose Entry Into Cells

• Water-Soluble: Cannot diffuse across membrane, requires transporters.
• Transporters: GLUT (Glucose Transporters), bidirectional.
  • Types of GLUT Receptors: Remembered using the mnemonic "BBB Ok Kids Lips are Pink Mother-Father"
    • GLUT1: Red blood cells, fetus, blood-brain barrier
    • GLUT2: Kidney, liver, pancreas, gastrointestinal tract
    • GLUT3: Placenta, neurons, kidney
    • GLUT4: Muscle, fat (adipose), insulin-dependent

Steps of Glycolysis

1. Glucose to Glucose 6-Phosphate
   • Enzymes: Hexokinase (muscle, various tissues), Glucokinase (liver)
   • Mechanism: ATP donates a phosphate group, producing ADP.
2. Glucose 6-Phosphate to Fructose 6-Phosphate
   • Enzymes: Phosphohexose isomerase
   • Process: Isomerization
3. Fructose 6-Phosphate to Fructose 1,6-bisphosphate
   • Enzymes: Phosphofructokinase-1 (PFK-1)
   • Irreversibility: This step is not reversible and highly regulated.
4. Fructose 1,6-bisphosphate to Dihydroxyacetone phosphate (DHAP) and Glyceraldehyde 3-phosphate (GA3P)
   • Enzyme: Aldolase
   • Interconversion: DHAP converts to GA3P via Triose phosphate isomerase (TPI).
5. Glyceraldehyde 3-Phosphate to 1,3-Bisphosphoglycerate
   • Enzyme: Glyceraldehyde 3-phosphate dehydrogenase
   • NAD+: NAD+ reduced to NADH, addition of an inorganic phosphate
6. 1,3-Bisphosphoglycerate to 3-Phosphoglycerate
   • Enzyme: Phosphoglycerate kinase
   • ATP Formation: Produces ATP from ADP
7. 3-Phosphoglycerate to 2-Phosphoglycerate
   • Enzyme: Phosphoglycerate mutase
8. 2-Phosphoglycerate to Phosphoenolpyruvate (PEP)
   • Enzyme: Enolase
9. Phosphoenolpyruvate to Pyruvate
   • Enzyme: Pyruvate kinase
   • ATP Formation: Produces ATP from ADP, irreversible step

Fate of Pyruvate

• Anaerobic Conditions: Convert to Lactic Acid
  • Enzyme: Lactate dehydrogenase
  • NADH: Regenerated to NAD+
  • Clinical Correlation: High lactate dehydrogenase levels indicate conditions like MI, ischemia.
• Aerobic Conditions: Converts to Acetyl-CoA (discussed in future lessons)

Summary

• Location: Cytoplasm
• Starting Substrate: Glucose (6-carbon)
• End Product: 2 Pyruvates (3-carbon each)
• ATP Production:
  • Gross: 4 ATP
  • Net: 2 ATP (used 2 ATP during initial steps)
• NADH Production: 2 NADH
• Process Type: Generally anaerobic, producing lactic acid in low oxygen conditions.

Next steps will cover the transition of pyruvate into acetyl-CoA under aerobic conditions.