Glycolyisis

Glycolysis Overview

• Glycolysis is the metabolic pathway that converts glucose into pyruvate, producing ATP and NADH in the process.

Initial Steps of Glycolysis

• Starting Materials:

  • Glucose (derived from food or stored as glycogen/starch)

  • Key enzymes involved:

    • Hexokinase - phosphorylates glucose to form glucose 6-phosphate.

    • Phosphoglucose isomerase - rearranges glucose 6-phosphate to fructose 6-phosphate.

Energy Investment Phase

• Phosphofructokinase transfers a phosphate (Pi) from ATP to fructose 6-phosphate, resulting in:

  • Fructose 1,6-bisphosphate (F1,6-BP)

• Aldolase splits F1,6-BP into:

  • 1 molecule of Glyceraldehyde 3-phosphate (G3P) and 1 molecule of Dihydroxyacetone phosphate (DHAP).

• Triose phosphate isomerase converts DHAP into G3P.

Energy Generation Phase

• NAD+ Reduction:

  • Glyceraldehyde 3-phosphate dehydrogenase transfers a hydrogen from G3P to NAD+ to form NADH.

• Formation of 1,3-bisphosphoglycerate (BPG):

  • A Pi from the cytoplasm is added to G3P, yielding BPG.

• Substrate-Level Phosphorylation:

  • Phosphate is transferred from BPG to ADP to form ATP, yielding:

    • 2 molecules of 3-phosphoglycerate (3PG) and 2 ATP molecules.

• Conversion Steps:

  • Phosphate relocates from the third carbon on 3PG to the second carbon to form 2-phosphoglycerate (2PG).

  • Water is removed from 2PG to form Phosphoenolpyruvate (PEP).

• Final Step:

  • Pyruvate kinase transfers a phosphate from PEP to ADP, resulting in:

    • Pyruvate and a second ATP for every molecule of PEP formed.

Important Enzymes in Glycolysis

1. Hexokinase

2. Phosphoglucose isomerase

3. Phosphofructokinase

4. Aldolase

5. Triose phosphate isomerase

6. Glyceraldehyde 3-phosphate dehydrogenase

7. Phosphoglycerate kinase

8. Phosphoglycerate mutase

9. Enolase

10. Pyruvate kinase

Summary of Glycolysis Products

• Net Yield from glycolysis per glucose molecule:

  • 2 Pyruvate

  • 2 ATP (net gain)

  • 2 NADH