Krebs Cycle

Krebs cycle -

a)also known as tricarboxylic acid cycle or citric acid cycle.

b)a cyclic series of reactions occurring in the mitochondria in which pyruvate is broken down to form carbon dioxide, H+ and ATP.

c)The H+ ions are accepted either by NAD+ or FAD and then sent to the electron transport system where they are converted into water with the formation of ATP.

  Formation of acetyl coenzyme A.

a)Pyruvate undergoes oxidative decarboxylation in which carbon dioxide is removed and dehydrogenation takes place.

b)Coenzyme A and NAD+ are required forming acetyl coenzyme A and NADH + H+.

 Formation of citrate

a) Acetyl coenzyme A that consists of two-carbon atoms then combines with a four-carbon oxaloacetate to form a six-carbon citrate

 Regeneration of oxaloacetate :

a)The citrate then undergoes a series of reactions through α-ketoglutarate and succinate to regenerate oxaloacetate

b)In this cyclic process, decarboxylation takes place twice, dehydrogenation takes place four times and formation of GTP from GDP and phosphate once.

Regeneration of oxaloacetate :

c)  During the dehydrogenation process, three times NAD+ and one time FAD are used as hydrogen acceptors forming NADH + H+ and FADH2 respectively.

Hence from one pyruvate,

•four NADH + H+,

•one FADH2 and

•one GTP are produced.