Krebs cycle or Link reaction . The reaction of pyruvate oxidation is 2x CH COCOOH 2NAD 2CoA 2xCH CO.CoA 2NADH 2H 2CO ↑ Pyruvate dehydrogenase complex consist of three distinct enzymes, such as . Pyruvate dehydrogenase . Dihydrolipoyil transacetylase .
Dihydrolipoyil dehydrogenase and five different coenzymes, TPP (Thymine Pyro Phosphate), NAD , FAD, CoA and lipoate . . . Krebs cycle or Citric acid cycle or TCA cycle: Two molecules of acetyl CoA formed from link reaction now enter into Krebs cycle.
It is named after its discoverer, German Biochemist Sir Hans Adolf Krebs ( ). The enzymes necessary for TCA cycle are found in mitochondrial matrix except succinate dehydrogenase enzyme which is found in mitochondrial inner membrane (Figure . ). Pyruvate dehydrogenase complex/ Mg Figure .
: Structure of Mitochondrion Stalk Sir Hans Adolf Krebs was born in Germany on th August . He was awarded Nobel Prize for his discovery of Citric acid cycle in Physiology in . TCA cycle starts with condensation of acetyl CoA with oxaloacetate in the presence of water to yield citrate or citric . Amphibolic nature Krebs cycle is primarily a catabolic pathway, but it provides precursors for various biosynthetic pathways there by an anabolic pathway too.
Hence, it is called amphibolic pathway . It serves as a pathway for oxidation of carbohydrates, fats and proteins. When fats are respiratory substrate they are first broken down into glycerol and fatty acid. Glycerol is converted into DHAP and acetyl CoA.
This acetyl CoA enter into the Krebs cycle. When proteins are the respiratory substrate they are degraded into amino acids by proteases. The amino acids after deamination enter into the Krebs cycle through pyruvic acid or acetyl CoA and it depends upon the structure. So respiratory intermediates form the link between synthesis as well as breakdown.
The citric acid cycle is the final common pathway for oxidation of fuel molecules like amino acids, fatty acids and carbohydrates. Therefore, respiratory pathway is an amphibolic pathway (Figure . ). Figure .