Pyruvate Oxidation & Krebs Cycle

STEP 2: PYRUVATE OXIDATION

Recall…

Recall Step 1 - Glycolysis

• Happens in the cytoplasm• Does not require oxygen (anaerobic)• Inefficient (net 2 ATP produced)

Glycolysis Summary

What went in:

• 1 Glucose• 2ATP• 2 NAD+

• 4 ADP• 4 Pi

What was produced:• 2 pyruvate• 2 ADP• 2 NADH + H+

• 4 ATP

Step 2 – Pyruvate Oxidation

Overview

The two pyruvate molecules formed in glycolysis are transported through the two mitochondrial membranes into the matrix

Within the matrix, enzymes catalyze the following three changes

Happens twice for every glucose molecule

Three Steps of Pyruvate Oxidation

1. A carboxyl group is removed as CO2

2. The remaining two-carbon molecule is oxidized by NAD+. This is a redox reaction – pyruvate is oxidized, and NAD+ is reduced

3. Coenzyme A (CoA) is attached to the carbon compound, forming acetyl-CoA

2 pyruvate + 2 NAD+ + 2 CoA 2 acetyl-CoA + 2 NADH + 2 CO2

Overall

The two molecules of acetyl-CoA enter the Krebs cycle The two molecules of NADH proceed to step 4 to

participate in oxidative phosphorylation The two CO2 molecules diffuse out of the cell as waste The two H+ molecules remain dissolved in the matrix No ATP is directly produced in this step

STEP 3: KREBS CYCLE

Overview

• also called the Citric Acid Cycle• named after the Nobel Prize winner who

discovered it• Occurs in the mitochondrial matrix• 8 step process• Remember that the Krebs Cycle happens

TWICE for every one molecule of glucose.

Overall

The Krebs cycle will produce the following products for every glucose molecule broken down

• 6 NADH• 2 FADH2• 2 ATP• 4 CO2