HL Bio: Unit 3.3 - Link Reaction and the Kreb Cycle

Link Reaction:

Conversion of Pyruvate into two-carbon acetyl groups 

Done within the mitochondria matrix

• Transporter proteins is used to take it from the outer membrane intro the mitochondrial matrix

3 steps to the link reaction

1. Decarboxylation: removal of CO₂ to change the 3 carbon into a 2 carbon molecule

2. Oxidation: Removal of 2 electrons → Accepted by NAD producing NADH

3. Acetyl Binding: This was produced by the last two steps and it binds to a complex carrier molecule Coenzyme A (CoA)

Coenzyme A (CoA)

• The complex carrier the acetyl group binds to forming Acetyl coenzyme A

Kreb Cycle

Oxidation and Decarboxylation of Acetyl groups 

Oxaloacetic

A four carbon atom which was in the mitochondria to begin with combines with the acetyl group forming citric acid (6 carbon compound)

Process of the Kreb Cycle

1. Decarboxylation: one of the two carbons added by the acetyl group are then oxidized off forming carbon dioxide 

2. Continues until both carbons are oxidized and only the original 4 carbons remain

   • Each Oxidation reduced one NAD+ to NADH

   • 2 NADH are produced - 4 per glucose

3. More reactions occurs on 4-carbon compound to form several products until it’s back to it’s original oxaloacetic form

   • Another NADH is produced - 2 per glucose

   • Coenzyme FAD is reduced to form FADH₂

     • 2 are produced per glucose

   • ADP is also reduced to ATP

     • 2 are made per glucose molecule

Total products from the kreb cycle

1. 6 NADH per glucose - 2 per pyruvate during oxidation and then one in the reactions converting it back to oxaloacetic

2. 2 FADH₂ are produced per glucose (1 each pyruvate)

3. 2 ATP’s are produced per glucose (1 per pyruvate)