Biology Times (^) March 19
Aerobic Respiration
Aerobic respiration is a metabolic process where reduced organic compounds are mobilised and
subsequently oxidised in controlled manner. The first stage of aerobic respiration Glycolysis.
Step II: Link Reaction
The link reaction is named thus because it links the products of glycolysis with the aerobic processes of the
mitochondria. Pyruvate is transported from the cytosol into the mitochondrial matrix by carrier proteins
on the mitochondrial membrane. Pyruvate combines with CoA to form acetyl CoA. In this reaction, 2
hydrogen and 1st CO 2 molecule are removed. Hence this reaction is called oxidative decarboxylation. This
reaction is catalysed by enzyme pyruvic acid dehydrogenase. The two hydrogen atoms are accepted by
NAD+ to form NADH 2.
Pyruvic acid dehydrogenase complex is made up of a decarboxylase, thiamine pyrophosphate (TPP), lipoic
acid, transacetylase and Mg2+.Step III: Kreb’s cycle/ citric acid cycle/ TCA cycle
Kreb’s cycle was discovered by Hans Kreb in 1937. Discovery of tricarboxylic acid or Kreb cycle or citric
acid cycle which consists of series of chemical reactions under aerobic conditions. The term citric acid
cycle refers to the first stable compound formed in the cycle, i.e., Citrate or citric acid. This cycle of
reactions are each regulated by a specific enzyme.Citric acid cycle is located in matrix of mitochondria. Plant mitochondria have two membranes, Smooth
outer membrane that completely surrounds a highly invaginated inner membrane. The invaginations
of inner membrane are known as Cristae. Region between two mitochondrial membranes are called
Intermembrane space. The aqueous phase contained within the inner membrane is referred as
Mitochondrial matrix.
Raw material of the kreb’s cycle is Acetyl CoA. It is formed from fatty acids by β-oxidation and from
pyruvic acid by oxidative decarboxylation.