MUSCLE PHYSIOLOGY

Detailed explanation-1: -Krebs’ cycle starts with condensation of acetyl group (acetyl CoA) with oxaloacetate (4-carbon compound) in the presence of a condensing enzyme citrate synthase to form a tricarboxylic, 6-carbon compound called citric acid. It is the 1st product of Krebs cycle.

Detailed explanation-2: -The first step is fusion of the acetyl group of acetyl-CoA with oxaloacetate, catalyzed by citrate synthase. CoA-SH and heat are released and citrate is produced.

Detailed explanation-3: -The Krebs cycle itself actually begins when acetyl-CoA combines with a four-carbon molecule called OAA (oxaloacetate) (see Figure above). This produces citric acid, which has six carbonatoms. This is why the Krebs cycle is also called the citric acid cycle.

Detailed explanation-4: -The citric acid cycle is called a cycle because the starting molecule, oxaloacetate (which has 4 carbons), is regenerated at the end of the cycle.

Detailed explanation-5: -The citric acid cycle begins with the transfer of a two-carbon acetyl group from acetyl-CoA to the four-carbon acceptor compound (oxaloacetate) to form a six-carbon compound (citrate). The citrate then goes through a series of chemical transformations, losing two carboxyl groups as CO2.