NEET BIOLOGY

Detailed explanation-1: -Fuel for the Krebs cycle comes from lipids (fats) and carbohydrates, which both produce the molecule acetyl coenzyme-A (acetyl-CoA). This acetyl-CoA reacts in the first step of the eight step sequence of reactions that comprise the Krebs cycle, all of which occur inside mitochondria of eukaryotic cells.

Detailed explanation-2: -The Krebs cycle, by itself, does not require the presence of oxygen; this element is necessary for the last stage of aerobic cellular respiration, i.e., oxidative phosphorylation. Organic molecules endowed with energy (carbohydrates, lipids, proteins) are split in previous reactions.

Detailed explanation-3: -The main function of the Krebs cycle is to produce energy, stored and transported as ATP or GTP.

Detailed explanation-4: -The Krebs cycle uses the two molecules of pyruvic acid formed in glycolysis and yields high-energy molecules of NADH and flavin adenine dinucleotide (FADH2), as well as some ATP. The Krebs cycle occurs in the mitochondrion of a cell (see Figure 6-1).

Detailed explanation-5: -The only reactants of the Krebs cycle proper are acetyl CoA and the aforementioned four-carbon molecule, oxaloacetate. The availability of acetyl CoA hinges on adequate amounts of oxygen being present to suit the needs of a given cell.