Glycolysis Lecture Notes 🧪

Introduction to Glycolysis

• Definition: Process of oxidizing glucose to produce energy.
• Glucose: A six-carbon molecule (C₆H₁₂O₆), a monosaccharide (simple sugar).
• End Product: Glycolysis converts glucose into two molecules of pyruvate (each a three-carbon molecule).

Glucose Transportation into Cells

• Issue: Glucose is water-soluble and cannot passively diffuse through the cell membrane.
• Solution: Requires specialized transporters known as GLUT transporters.
• Types of GLUT Transporters: GLUT1, GLUT2, GLUT3, GLUT4, involved in different tissues and having different functions.

GLUT Transporter Mnemonic: BBB OK Kids Lips Mother Father

• GLUT1:

  • Blood (red blood cells)
  • Baby (fetus)
  • Blood-brain barrier

• GLUT2:

  • Kidney
  • Liver
  • Pancreas

• GLUT3:

  • Placenta
  • Neurons
  • Kidney

• GLUT4:

  • Muscle
  • Fat (adipose tissue)

• Special Note: GLUT4 is insulin dependent, whereas GLUT1, GLUT2, and GLUT3 are insulin independent.

Steps of Glycolysis

1. Glucose to Glucose-6-Phosphate

   • Enzymes: Hexokinase (muscle) or Glucokinase (liver)
   • ATP: Converts ATP to ADP for the phosphate group.

2. Glucose-6-Phosphate to Fructose-6-Phosphate

   • Enzyme: Phosphohexose isomerase
   • Process: Isomerization (aldehyde to ketone)

3. Fructose-6-Phosphate to Fructose-1,6-Bisphosphate

   • Enzyme: Phosphofructokinase-1 (PFK-1)
   • ATP: Another ATP to ADP conversion.

4. Fructose-1,6-Bisphosphate Split

   • Enzyme: Aldolase
   • Products: Dihydroxyacetone phosphate (DHAP) and Glyceraldehyde-3-Phosphate (G3P)
   • Conversion: DHAP converts to G3P via Triose Phosphate Isomerase.

5. G3P to 1,3-Bisphosphoglycerate (1,3-BPG)

   • Enzyme: Glyceraldehyde-3-Phosphate Dehydrogenase
   • NAD+: Converts NAD+ to NADH, adding inorganic phosphate (Pi).

6. 1,3-BPG to 3-Phosphoglycerate (3-PG)

   • Enzyme: Phosphoglycerate Kinase
   • ATP Production: Converts ADP to ATP (produces 2 ATP per glucose).

7. 3-PG to 2-Phosphoglycerate (2-PG)

   • Enzyme: Phosphoglycerate Mutase
   • Process: Phosphate shifts from third to second carbon.

8. 2-PG to Phosphoenolpyruvate (PEP)

   • Enzyme: Enolase
   • Process: Formation of enol structure.

9. PEP to Pyruvate

   • Enzyme: Pyruvate Kinase
   • ATP Production: Converts ADP to ATP (produces 2 ATP per glucose).

Overview of Glycolysis Products

• Starting Substrate: Glucose
• Location: Cytoplasm of the cell
• End Product: 2 Pyruvate molecules
• Net ATP Gain: 2 ATP (4 ATP gross but 2 used)
• NADH: 2 NADH produced
• Anaerobic Process: Generally occurs in the absence of oxygen (leads to lactic acid production).

Fate of Pyruvate

• Anaerobic Conditions:

  • Conversion: Pyruvate to Lactic Acid
  • Enzyme: Lactate Dehydrogenase
  • Result: Decreasing pH, potential metabolic acidosis.

• Aerobic Conditions: Will follow up in the next lecture covering the transition step to Acetyl-CoA.

Key Points

• Glycolysis is a crucial energy-producing pathway occurring in the cytoplasm.
• Uses glucose to produce ATP, NADH, and pyruvate.
• Regulated by specific enzymes at key steps that determine its direction and outcome, under both anaerobic and aerobic conditions.