Mechanism of Respiration

                  The process of respiration completes in 4 major phases:

1. Glycolysis :

             It is common to aerobic and anaerobic respiration. It occur in cytoplasm. In this process , oxygen is not necessary and a glucose molecule breaks to form two molecules of pyrubic acid under the action of several enzymes.

2. Oxidative decarboxylation of pyrubic acid:

            Pyrubic acid is the end  product of glycolysis that don’t enter into kreb cycle directly so three carbon carbon change into 2 carbon atom, acetic acid by decarboxylation. Acetic acid enters into mitochondrial unit and react with Co-enzyme A to form acetyl Co-enzyme A. In this reaction, two hydrogen atom are released , accepted by NAD to form NADH_2.

                                       In glycolysis, two molecules of pyrubic acid, two molecules of NADH₂ and two molecules of ATP are formed.

3. Kreb’s Cycle :

          Acetyl C-enzyme A enters into matrix of mitochondria and decarboxylated dehydrogenated into CO₂, water, NADH₂ and FADH₂ in presence of oxygen to release ATP energy in kreb cycle. The first metabolic compund of Kreb’s  cycle is 3-carbon atom, cytric acid. So, it is also called tricarboxylic acid cycle. It was discovered by Kreb in 1945 and got Noble Prize in 1950.