KREB’S CYCLE

Discovered by Hans Adolf Krebs who won the nobel prize in 1953

Occurs in the mitochondrial matrix

A cyclical metabolic pathway with 8 steps which begins with acetyl-CoA and and ends with oxaloacetate- Two acetyl-CoA molecules enter for every glucose molecule consumed

KREB’S CYCLE

Each molecule of acetyl-CoA has two original carbon atoms from the starting glucose

These carbons are released in Kreb’s from as carbon dioxide- The original glucose molecule is completely consumed

All that remains from the original glucose molecule is most of it’s energy stored in the form of ATP and electron carriers

- 4 ATP: 2 glycolysis, 2 kreb’s- 10 NADH: 2 glycolysis, 2 pyruvate oxidation, 6 kreb’s- 2 FADH2: kreb’s

KREB’S CYCLE

KREB’S CYCLE

KREB’S CYCLE

Overall Equation for Kreb’s cycle:

OAA + Acetyl-CoA + ADP + Pi + 3NAD+ + FAD CoA + ATP + 3 NADH + 3H+ + FADH2 + 2 CO2 +

OAA

KREB’S CYCLE

1. Acetyl-CoA (2 original carbons) reacts with oxaloacetate to produce citrate (6 carbons)

Two citrate are produced per glucose

KREB’S CYCLE

2. Citrate (6 carbons) is converted to Isocitrate (6 carbons)

Two isocitrate are produced per glucose

KREB’S CYCLE

3. Isocitrate (6 carbons) is converted to α-ketoglutarate (5 carbons)

- Carbon dioxide is given off- NAD+ is reduced to NADH*** The oxidation of CO2 is coupled to the reduction of NAD+

Two α-ketoglutarate, two carbon dioxide and two NADH are produced per glucose

KREB’S CYCLE

4. α-ketoglutarate (5 carbons) is converted to Succinyl-CoA (4 carbons)- Carbon dioxide is given off- NAD+ is reduced to NADH*** The oxidation of CO2 is coupled to the reduction of NAD+

Two succinyl-CoA, two carbon dioxide and two NADH are produced per glucose

KREB’S CYCLE

5. Succinyl Co-A (4 carbons) is converted to Succinate (4 carbons)

- ATP is generated by substrate level phosphorylation** Phosphate replaces CoA, Phosphate is then added to GTP, Phosphate is then transferred to ADP to form ATP

Two succinate and two ATP are produced per glucose

KREB’S CYCLE

6. Succinate (4 carbons) is converted to Fumarate (4 carbons), oxidation reaction

- FAD is reduced to FADH2

Two fumarate and two FADH2 are produced per glucose

KREB’S CYCLE

7. Fumarate (4 carbons) is converted to Malate (4 carbons)

- Using the addition of water

Two malate are produced per glucose

KREB’S CYCLE

8. Malate (4 carbons) is converted to oxaloacetate (4 carbons,), oxidation reaction- NAD+ is reduced to NADH

Two oxaloacetate and two NADH are produced per glucose

KREB’S CYCLE

Recall:- 4 ATP: 2 glycolysis, 2 kreb’s- 10 NADH: 2 glycolysis, 2 pyruvate oxidation, 6 kreb’s- 2 FADH2: kreb’s

This is not enough!!!

KREB’S CYCLE