Glycolysis is an anaerobic process & takes place in cytosol, through which one glucose molecules is breakdown into two molecules of three-carbon pyruvate. The glycolysis of each glucose molecule generates 2 ATP molecules. ATP synthesis from anaerobic process is via glycolysis of glucose in the presence of various enzymes.
Glucose + 2 NAD+ + 2 Pi + 2 ADP → 2 pyruvate + 2 NADH + 2 ATP + 2 H+ + 2 H2O + heat
Citric acid cycle:
The pyruvate generated by the glycolysis is converted into acetyl-CoA that enters into the citric acid cycle. Citric acid cycle involves a series of reactions that occur in the presence of oxygen. Citric acid cycle generates NADH, which enters into the oxidative phosphorylation process. This cycle occurs in mitochondrial matrix and generates one ATP molecule only.
Acetyl co-A + 3 NAD+ + FAD+ + inorganic phosphate + GDP + 2 water molecules -----> Coenzyme A-SH + 3 NADH + 3H+ + FADH2 + 1 GTP + 2 CO2
Oxidative phosphorylation: this process involves electron transport in mitochondria, where a greatest amount of ATP is produced through electron transport chain.
Glycolysis (breakdown of glucose), oxidation of fatty acids and citric acid cycle releases NADH (hydrohenated nicotinamide adenine dinucleotide) and FADH2 (hydrogenated flavin adenine dinucleotide) molecules. These molecules carry electrons with high transfer potential. These electrons reduce the oxygen present in the mitochondria; this process produces a very high amount of energy (in the form of ATP (adenosine triphosphate)).
“Oxidative phosphorylation (occurs in cristae of mitochondria)” is an aerobic process that involves a series of reactions, which include the transfer of electrons from the NADH or FADH2 to oxygen. This process involves the transfer of electrons (oxidation) by a series of electron carriers (electron transport system (ETS)) and attachment of phosphate group (phosphorylation). Aerobic ATP synthesis in the presence of oxygen takes place in mitochondria as describe below.
FADH2 is not be re-oxidized by complex I of the respiratory chain while NADH becomes a substrate for Complex I.
FADH2 can be reoxidized by Complex II of the respiratory chain to generate 2 ATP (stores less energy) while NADH is a substrate to generate 3 ATP (provides more energy) can be reoxidised by complex I. NADH donates a pair of electrons in a downhill movement followed by generation of ATP via complex I.
Thus, the options (a), (b) and (d) are incorrect.
Oxidative phosphorylation: this process involves electron transport in mitochondria, where a greatest amount of ATP is produced through electron transport chain.
Therefore, the correct option is – c. electron transport chain.