CHAPTER 34: TRICARBOXYLIC ACID CYCLE

The TCA cycle, also known as the Citric Acid or Krebs Cycle, is a metabolic pathway that occurs in the mitochondrial matrix and serves as a major integration center for coordinating carbohydrate, lipid, and protein metabolism.

TCA cycle

The liver is the major organ in which the TCA cycle and other metabolic processes occur to a significant extent. Damage or replacement of hepatocytes in the liver can have profound repercussions on metabolic pathways.

Liver

Citrate synthase is the enzyme that catalyzes the first reaction of the TCA cycle, which involves the synthesis of citrate from acetyl-CoA and oxaloacetate. It is inhibited by high concentrations of ATP, citrate, and long-chain fatty acyl-CoA.

Citrate synthase

Isocitrate dehydrogenase is the enzyme that catalyzes the dehydrogenation of isocitrate to form oxalosuccinate and the subsequent decarboxylation to produce alpha-ketoglutarate. It is an important enzyme in the TCA cycle and is inhibited by ATP and NADH.

Isocitrate dehydrogenase (ICD)

Succinate thiokinase, also known as succinyl-CoA synthetase, is the enzyme that catalyzes the conversion of succinyl-CoA to succinate in the TCA cycle. This reaction generates a high-energy phosphate, either ATP or GTP, at the substrate level.

Succinate thiokinase

Fumarase, also called fumarate hydratase, is the enzyme that catalyzes the addition of water to fumarate to produce malate in the TCA cycle.

Fumarase

Malate dehydrogenase is the enzyme that catalyzes the reversible conversion of malate to oxaloacetate in the TCA cycle. It requires NAD+ as a cofactor and plays a role in gluconeogenesis in liver tissue.

Malate dehydrogenase

The TCA cycle generates reducing equivalents in the form of NADH and FADH2, which are passed on to

ATP production