Explain the Kreb'S Cycle with Reaction
Answers
Explanation:
ANSWER
The reactions which help in converting pyruvic acid to carbon dioxide and water in mitochondria is called Krebs cycle. It is also known as citric acid or tricarboxylic acid cycle (TCA cycle).
In the first reaction of citric acid cycle, acetyl CoA combines with the oxaloacetic acid to form citric acid. This reaction is catalysed by citric acid synthetase. Citric acid contains three carboxylic acid groups. Citric acid is dehydrated to form cis-aconitic acid in the presence of aconitase. The same enzyme aconitase catalyses the formation of isocitric acid from the cis-aconitic acid by the addition of the molecule of water. Citric acid, cis-aconitic acid, and isocitric acid contain three carboxylic acid groups. The isocitric acid is oxidatively decarboxylated to α−α−ketoglutaric acid. This reaction is catalysed by an isocitric dehydrogenase. During this reaction, one NADH
2
is formed. The α-ketoglutaric acid is oxidatively decarboxylated to form succinyl co-a. This reaction is catalysed by an alpha-ketoglutaric dehydrogenase. The energy released during this reaction is conserved in NADH
2
. The succinyl-CoA is hydrolysed to succinic acid in the presence of succinyl co-a synthetase. In this reaction, ADP is phosphorylated to ATP. This is called substrate level phosphorylation. The succinic acid is oxidised to form fumaric acid by a succinic dehydrogenase. FAD++ is reduced to FADH
2
. The fumaric acid is converted to malic acid by the addition of a molecule of water. This reaction is catalysed by fumarase. The malic acid is oxidised to oxaloacetic acid by the enzyme malic dehydrogenase.
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Explanation:
The citric acid cycle (CAC) – also known as the TCA cycle (tricarboxylic acid cycle) or the Krebs cycle – is a series of chemical reactions used by all aerobic organisms to release stored energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins. In addition, the cycle provides precursors of certain amino acids, as well as the reducing agent NADH, that are used in numerous other reactions. Its central importance to many biochemical pathways suggests that it was one of the earliest components of metabolism and may have originated abiogenically. Even though it is branded as a 'cycle', it is not necessary for metabolites to follow only one specific route; at least three segments of the citric acid cycle have been recognized.[5]
The name of this metabolic pathway is derived from the citric acid (a tricarboxylic acid, often called citrate, as the ionized form predominates at biological pH that is consumed and then regenerated by this sequence of reactions to complete the cycle. The cycle consumes acetate (in the form of acetyl-CoA) and water, reduces NAD+ to NADH, releasing carbon dioxide. The NADH generated by the citric acid cycle is fed into the oxidative phosphorylation (electron transport) pathway. The net result of these two closely linked pathways is the oxidation of nutrients to produce usable chemical energy in the form of ATP.
In eukaryotic cells, the citric acid cycle occurs in the matrix of the mitochondrion. In prokaryotic cells, such as bacteria, which lack mitochondria, the citric acid cycle reaction sequence is performed in the cytosol with the proton gradient for ATP production being across the cell's surface (plasma membrane) rather than the inner membrane of the mitochondrion. The overall yield of energy-containing compounds from the TCA cycle is three NADH, one FADH2, and one GTP.