AP BIOLOGY

Detailed explanation-1: -The Krebs cycle starts with pyruvic acid from glycolysis. Each small circle in the diagram represents one carbon atom. For example, citric acid is a six carbon molecule, and OAA (oxaloacetate) is a four carbon molecule. Follow what happens to the ca rbon atoms as the cycle proceeds.

Detailed explanation-2: -In order to enter the Kreb’s Cycle pyruvate must first be converted into Acetyl-CoA by pyruvate dehydrogenase complex found in the mitochondria.

Detailed explanation-3: -Fuel for the Krebs cycle comes from lipids (fats) and carbohydrates, which both produce the molecule acetyl coenzyme-A (acetyl-CoA). This acetyl-CoA reacts in the first step of the eight step sequence of reactions that comprise the Krebs cycle, all of which occur inside mitochondria of eukaryotic cells.

Detailed explanation-4: -Glycolysis is a linear metabolic pathway of enzyme-catalyzed reactions that converts glucose into two molecules of pyruvate in the presence of oxygen or two molecules of lactate in the absence of oxygen.

Detailed explanation-5: -Prior to entry into this cycle, pyruvate must be converted into a 2-carbon acetyl-CoenzymeA (acetyl-CoA) unit. Figure 15.2. 1: After glycolysis, two 3-carbon pyruvates enter the mitochondria, where they are converted to two 2-carbon acetyl-CoenzymeA (CoA) molecules. Acetyl-CoA then enters the Krebs Cycle.