Biochemistry Lecture No. 17: The Citric Acid Cycle
Thursday October 18 , 2012
The Mitochondrion & Its Regions:
-The outer mitochondrial membrane has many pores to allow small molecules to cross. The inner
mitochondrial membrane (IM membrane) prevents small molecules from crossing, unless a special
pathway exists. The cristae are folds of the IM membrane that provide high surface area. The
mitochondrial matrix is the space enclosed by the IM membrane. The origins of mitochondria involve
the endosymbiosis of symbiotic aerobic bacteria into eukaryotic cells billions of years ago.
-Pyruvate oxidation occurs in two stages: the decarboxylation of pyruvate to form acetyl coenzyme A
(acetyl CoA) and the oxidation of the acetyl group in acetyl CoA in the Citric Acid (Kreb’s) Cycle.
-Coenzyme A (or CoA) is a carrier molecule that contains a thiol group (SH) on its end. When attached to
an acetyl group, a high energy bond is formed between the acetyl and the thiol group of CoA.
The Formation Of Acetyl CoA From Pyruvate:
-The pyruvate dehydrogenase complex is the enzyme responsible for the conversion of pyruvate to
acetyl CoA. Both acetyl CoA and NADH are competitive inhibitors (bind to the active site) and will inhibit
further catalysis by pyruvate dehydrogenase