Kreb’s cycle

Krebs Cycle is a part of Cellular Respiration

Cellular respiration is a four-stage process.

1. Glycolysis: Partial oxidation of a glucose molecule to form 2 molecules of pyruvate. This process takes place in the cytosol.

2. Formation of Acetyl CoA: Pyruvate formed in glycolysis enters the mitochondrial matrix. It undergoesoxidative decarboxylation to form two molecules of Acetyl CoA. The reaction is catalyzed by the pyruvate dehydrogenase enzyme.

2Pyruvate+2NAD++2COA ————————>2Acetyl CoA+2NADH+CO₂

Pyruvate oxidation steps:

• Step 1. A carboxyl group is snipped off of pyruvate and released as a molecule of carbon dioxide, leaving behind a two-carbon molecule.
• What causes the carboxyl group of the pyruvate to be removed?
• The enzyme ‘pyruvate dehydrogenase’ pulls away the carboxyl group, resulting in the release of Carbon Dioxide, leaving the Acetyl group behind for binding with CoA.

• Step 2. The two-carbon molecule from step 1 is oxidized, and the electrons lost in the oxidation are picked up by NAD+ to form NADH
• What causes the NAD+ to form NADH+ ?

The carboxyl group does give the acetyl group a negative charge. It shows the CoA attached to sulfur and Hydrogen in step 2. The NAD+ comes to snatch up a H ion that the COA-SH left.

• Step 3. The enzyme-bound acetyl group is transferred to COA, producing a molecule of acetyl CoA. This molecule of acetyl CoA is then further converted to be used in the next pathway of metabolism, the citric acid cycle.

Krebs Cycle is a part of Cellular Respiration

Cellular respiration is a four-stage process.

3. Krebs cycle (TCA cycle or Citric Acid Cycle): It is the common pathway for complete oxidation of carbohydrates, proteins and lipids as they are metabolised to acetyl coenzyme A or other intermediates of the cycle. The Acetyl CoA produced enters the Tricarboxylic acid cycle or Citric acid cycle. Glucose is fully oxidized in this process. The acetyl CoA combines with 4-carbon compound oxaloacetate to form 6C citrate. In this process, 2 molecules of CO2 are released and oxaloacetate is recycled. Energy is stored in ATP and other high energy compounds like NADH and FADH2.

4. Electron Transport System and Oxidative Phosphorylation: ATP is generated when electrons are transferred from the energy-rich molecules like NADH and FADH2, produced in glycolysis, citric acid cycle and fatty acid oxidation to molecular 02 by a series of electron carriers. O2 is reduced to H2O. It takes place in the inner membrane of mitochondria.