Match the respiratory substrate/enzyme with its entry or action: List I | List II A. Fatty acids | 1. Degrade proteins B. Glycerol | 2. Enter pathway…

The correct Answer is A-2, B-3, C-4, D-1

Explanation

The question pertains to the metabolic pathways of different respiratory substrates (fatty acids, glycerol, amino acids) and the action of an enzyme (proteases) within cellular respiration. It requires matching these components with their respective entry points into the respiratory pathway or their specific function.

Statement-wise Analysis

1. A. Fatty acids - 2. Enter pathway as Acetyl CoA
   Correct: Fatty acids are broken down through beta-oxidation into two-carbon units, which are then converted into Acetyl CoA. Acetyl CoA subsequently enters the Krebs cycle.
2. B. Glycerol - 3. Enter pathway as PGAL
   Correct: Glycerol, derived from fats, is phosphorylated to glycerol phosphate and then oxidized to dihydroxyacetone phosphate (DHAP). DHAP is an isomer of phosphoglyceraldehyde (PGAL), which is an intermediate in glycolysis. Thus, glycerol enters the respiratory pathway as PGAL (or DHAP).
3. C. Amino acids - 4. Enter at various stages after deamination
   Correct: Amino acids, after deamination (removal of the amino group), are converted into various intermediates of the respiratory pathway. Depending on the specific amino acid, these intermediates can enter at different points, such as pyruvate, Acetyl CoA, or intermediates of the Krebs cycle.
4. D. Proteases - 1. Degrade proteins
   Correct: Proteases are enzymes that catalyze the breakdown of proteins into smaller polypeptides or individual amino acids. This is their primary function in digestion and metabolism.

Key Takeaway

Different macromolecules (fats, proteins) are broken down into their constituent units, which then enter the common respiratory pathway at specific intermediate stages, such as Acetyl CoA, PGAL, or Krebs cycle intermediates, to generate energy. Proteases are enzymes responsible for protein degradation.