Question

Gateway of Krebs cycle?

Answer 1

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The citric acid cycle (CAC) – also known as the TCA cycle (tricarboxylic acid cycle) or theKrebs cycle is a series of chemical reaction  used by all aerobic organisms to release stored energy through the oxidation  of acetyl-CoA derived from carbohydrates, fats and proteins into (ATP) and carbon dioxide . In addition, the cycle provides precursor  of certain amino acids, as well as the reducing agent NADHthat are used in numerous other reactions. Its central importance to many biochemical pathways suggests that it was one of the earliest established components of cellular 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.

The name of this metabolic pathway is derived from the critic acid (a type of 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 acetly-CoA) and water, reduces NAD+to NADH, and produces carbon dioxide as a waste byproduct. 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