The tricarboxylic acid cycle occurs in a collection of enzymes in the mitochondrial matrix that is organized in a cyclic metabolic pattern. These enzymes include succinate dehydrogenase, which enters the membrane-bound ET route through the inner mt-membrane, and dehydrogenases that congregate in the NADH pool. At the point where pyruvate enters the TCA cycle via acetyl-CoA, citrate synthase serves as a marker enzyme for the cycle. Thus, it is the central component of the electron transfer pathway, located downstream of the outer mt-membrane and upstream of the inner membrane-bound ET pathway (mET-pathway). Fatty acid oxidation also referred to as -oxidation requires sections of the TCA cycle.
Hans Krebs proposed the intricate cycle, which earned it the name Krebs cycle. In 1953, he received the Nobel prize for his contribution. The acetyl group of acetyl-CoA is oxidized to make two molecules of CO2 in a succession of eight steps, while also producing one ATP. Additionally, reduced high-energy molecules like NADH and FADH2 are created.
Krebs Cycle Phases
It involves eight steps. In the matrix of mitochondria, the Krebs cycle or TCA cycle occurs in aerobic conditions.
Step 1: Coenzyme A is released during the condensation of acetyl CoA with the 4-carbon molecule oxaloacetate to create 6C citrate. Citrate synthase is the catalyst for the process.
Step 2: Isocitrate, the isomer of citrate, is produced. This process is catalyzed by the enzyme aconitase.
Step 3: Isocitrate is dehydrogenated and decarboxylated to produce 5C -ketoglutarate. The release of CO2 in a molecular form. The reaction is catalyzed by isocitrate dehydrogenase. It is an enzyme that depends on NAD+. NADH is created from NAD+.
Step 4, succinyl CoA, a 4C molecule, is created by the oxidative decarboxylation of -ketoglutarate. The enzyme complex known as -ketoglutarate dehydrogenase facilitates the process. NAD+ is changed to NADH, which results in the emission of one CO2 molecule.
Step 5: Succinate is created by succinyl CoA. The reaction is catalyzed by the succinyl CoA synthase enzyme. Along with that, GDP is phosphorylated at the substrate level to produce GTP. ATP is created when GTP transfers its phosphate to ADP.
In step 6 : the enzyme succinate dehydrogenase converts succinate to fumarate. As a result, FAD is changed into FADH2.
Step 7: By adding one H2O, fumarate is transformed into malate. Fumarase is the enzyme that is catalyzing this reaction.
In step 8, malate is dehydrogenated to create oxaloacetate, which joins forces with an additional acetyl CoA molecule to initiate a new cycle. Removed hydrogens are transferred to NAD+ to create NADH. The reaction is catalyzed by malate dehydrogenase.