Citric Acid Cycle

Citric Acid Cycle

Also know as the Krebs Cycle
The citric acid cycle completes the energy yielding oxidation of orgainic molecules
If molecular oxygen is present, pyruvate enters the mitochondrion. Here the enzymes of the krebs cycle complete the oxidation of the organic fuel. As the pyruvate enters the mitochondrion through the active transport, it is converted to a compound known as acetyl coenzyme (acetyl CoA).

Process Overview

1.. Acetyl CoA adds its 2-carbon acetyl group to oxaloacetate, which produces citrate.
2.. By the removal of a water molecule and addition of another, citrate is converted into isocitrate.
3.. Citrate losses a CO2, the result looses an electron, reducing NAD+ to NADH.
4.. Another CO2 is lost, and the result is again oxidized reducing NAD+ to NADH. The remaining molecule next attached to CoA by an unstable bond.
5.. CoA is then displaced by a phosphate group, which is transferred to GDP, forming GTP and then to ATP, this is by substrate-level phosphorylation, (process in which ATP is made by enzyme transfer of a phosphate group from an organic substrate to ATP.)
6.. Two hydrogens are transferred to FAD, forming FADH2 and oxidizing succinate.
7.. The addition of a H2O rearranges bonds in the substrate. The substrate is oxidized reducing NAD+ to NADH and regenerating oxloacetate.