AP BIOLOGY

Detailed explanation-1: -During glycolysis, glucose is broken down into two three-carbon molecules of pyruvate. The mitochondrial pyruvate dehydrogenase complex then catalyzes the oxidative decarboxylation of pyruvate to produce acetyl-CoA, a two-carbon acetyl unit that is ligated to the acyl-group carrier, CoA [6].

Detailed explanation-2: -The link reaction occurs in the mitochondrial matrix. In the first step, carbon dioxide and hydrogen are removed from two pyruvate molecules, producing two acetyl groups. The hydrogen removed is transferred to NAD, reducing it. In the second step, coenzyme A combines with the acetyl group to form acetyl CoA.

Detailed explanation-3: -Acetyl-CoA is synthesized in mitochondria by a number of reactions: oxidative decarboxylation of pyruvate; catabolism of some amino acids (e.g., phenylalanine, tyrosine, leucine, lysine, and tryptophan); and -oxidation of fatty acids (see earlier).

Detailed explanation-4: -During the link reaction, a carbon atom is removed from pyruvate, forming carbon dioxide. This converts pyruvate into a two-carbon molecule called acetate. Hydrogen is also removed from pyruvate in the conversion into acetate, which is picked up by the coenzyme NAD to form reduced NAD.

Detailed explanation-5: -In the Krebs cycle, acetyl coenzyme A produced by the link reaction joins the 4-carbon compound oxaloacetic acid (or oxaloacetate) to form the 6-carbon compound citric acid (or citrate). Then, in a series of reactions, oxaloacetic acid is regenerated from citric acid.