Question

What is the main function of the CAC with respect to energy metabolism?

Answer 1

Citric Acid Cycle

The citric acid cycle (CAC) or TCA cycle (tricarboxylic acid cycle) or the Krebs cycle is a cyclic chemical reactions used by the aerobic organisms to produce energy by the oxidation of acetyl-CoA which is derived from carbohydrates, fats, and proteins, into adenosine triphosphate (ATP) and carbon dioxide.This cycle provides precursors of certain amino acids, as well as the reducing agent NADH, GTP and FADH2 that are used in numerous other reactions. It is central importance reaction for many biochemical pathway. Even though it is called  as a 'cycle', but it is not necessary for metabolites to strictlelly follow the only one specific route; at least three segments of the citric acid cycle have been recognized.

Thhe cycle consumes acetate (in the form of acetyl-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, CAC occurs in the matrix of the mitochondrion. In prokaryotic cells, such as bacteria, which lack mitochondria, the CAC reaction 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.