Steps of the Krebs Cycle (Citric Acid Cycle):

The Krebs cycle, also known as the citric acid cycle or tricarboxylic acid (TCA) cycle, is a series of enzymatic reactions that take place in the mitochondrial matrix. These steps occur for each acetyl-CoA molecule entering the cycle (two for each glucose molecule). Here are the key steps:

1. Acetyl-CoA Entry: Acetyl-CoA combines with oxaloacetate to form citrate, a six-carbon compound.

2. Isomerization: Citrate is isomerized to isocitrate.

3. First Oxidation: Isocitrate is oxidized to release carbon dioxide (CO2), and it also generates the first NADH of the cycle. This reaction converts isocitrate into alpha-ketoglutarate.

4. Second Oxidation: Alpha-ketoglutarate is oxidized, releasing another molecule of CO2 and generating a second NADH. It is converted into succinyl-CoA.

5. Substrate-Level Phosphorylation: Succinyl-CoA is converted into succinate, with the concomitant formation of GTP (or ATP).

6. Oxidation and Electron Transfer: Succinate is oxidized to fumarate, producing FADH2.

7. Hydration: Fumarate is hydrated to form malate.

8. Final Oxidation: Malate is oxidized to oxaloacetate, generating another NADH.

The cycle continues as oxaloacetate is regenerated to combine with another acetyl-CoA molecule.