Question

The ultimate respiratory substrate, yielding the maximum number of ATP molecules, is
A. Glycogen
B. Ketogenic amino acid
C. Glucose
D. Amylose

Answer 1

Hint:
The breakdown of different respiratory substrates to release energy in the form of ATP molecules is called respiration. It can take place either in the presence of oxygen or in the absence of oxygen. The organic nutrients oxidized to release energy are called respiratory substrates. It can be carbohydrates, lipids or proteins.

Complete step by step answer:
The amount of energy released during the oxidation of respiratory substrates is different for different substrates.
Carbohydrates are stored in the tissues of the body in the form of glycogen and on hydrolysis forms glucose. Glycogen is not directly used to release energy as it is a complex polysaccharide and thus is first converted into a simple monosaccharide called glucose and then glucose is used as the respiratory substrate. The glucose is first converted into a three-carbon molecule of pyruvate in the cytoplasm and then is further broken down into carbon dioxide and water. The oxidation of glucose releases 38 molecules of ATP.
An amino acid that can be directly degraded into acetyl-CoA is called a ketogenic amino acid. Lysine and leucine are pure ketogenic amino acids. The acetyl-CoA enters the citric acid cycle and produces 22 molecules of ATP after oxidative phosphorylation.
A component of starch that consists of long, unbranched chains of polysaccharides is called amylose. Amylose is also first converted into glucose and then the energy is released in the form of ATP.
Thus, this concludes that the respiratory substrate yielding the maximum number of ATP molecules is glucose.
Hence, the correct answer is Glucose.

Option ‘C’ is correct

Note:
ATP (Adenosine triphosphate) is known as the energy currency of the cell and an excellent energy storage molecule due to the phosphate groups that link through the phosphodiester bonds. These bonds are high-energy bonds due to the electronegative charges that are exerting a repelling force between the phosphate groups and a significant amount of energy is stored within these phosphate-phosphate bonds.