GLYCOLYSIS, KREBS CYCLE • CLS Period 1 - Glycolysis, the Krebs Cycle, the ETS, and Metabolism and Respiration

Glycolysis and the TCA Cycle

In the first five steps of glycolysis, one six carbon molecule of glucose is split into two 3-carbon compounds. 2 molecules of ATP are required to prime these reactions. In the second phase of glycolysis, glyceraldehyde-3-phosphate is converted to pyruvate. These reactions yield 4 molecules of ATP, 2 for each molecule of pyruvate produced. The net gain of ATP in glycolysis, therefore, is 4 minus 2, or 2.

The two pyruvate molecules that resulted from glycolysis then go through the Krebs or Tricarboxylic acid (TCA) cycle. First, they are converted into acetyl CoA, and then begin as citrate, a six-carbon molecule with three carboxylic acid groups (note the name tricarboxylic acid). A series of eight steps is performed, and overall (per pyruvate molecule) three carbons are lost as CO₂, 3 NAD⁺ molecules are converted into NADH/H⁺, one ADP is converted to ATP through substrate level phosphorylation, and one FAD molecule is converted into FADH₂. This translates into a maximum net gain of 32 ATP, after all the NADH/H⁺ and the FADH₂ molecules are cashed in in the Electron Transport Phosphorylation.

Hosted by www.Geocities.ws