Options:

α-Ketoglutarate, Ribose 5-phosphate, 3-Phosphoglycerate, and Phosphoenolpyruvate serve as key metabolic intermediates providing carbon skeletons for amino acid biosynthesis, particularly glutamate, histidine, serine, and phenylalanine.

Correct Matching

• P. α-Ketoglutarate → ii. Glutamate: α-Ketoglutarate undergoes reductive amination or transamination to form glutamate directly, serving as the precursor for the α-ketoglutarate family of amino acids (glutamate, glutamine, proline, arginine).​​

• Q. Ribose 5-phosphate → i. Histidine: Ribose 5-phosphate converts to phosphoribosyl pyrophosphate (PRPP), the starting point for histidine biosynthesis via ATP-phosphoribosyl transferase.​

• R. 3-Phosphoglycerate → v. Serine: 3-Phosphoglycerate oxidizes to 3-phosphohydroxypyruvate, then transaminates to phosphoserine, and dephosphorylates to serine.​

• S. Phosphoenolpyruvate → iv. Phenylalanine: Phosphoenolpyruvate (PEP) combines with erythrose-4-phosphate in the shikimate pathway to form chorismate, leading to phenylalanine.​

Option Analysis

Option (A) P-ii; Q-i; R-v; S-iv matches all correct precursors above.​

Option (B) P-iii; Q-ii; R-i; S-v incorrect: α-Ketoglutarate links to glutamate (ii), not aspartate (iii, from oxaloacetate); Ribose 5-phosphate to histidine (i), not glutamate; 3-Phosphoglycerate to serine (v), not histidine.​

Option (C) P-iv; Q-iii; R-ii; S-v incorrect: α-Ketoglutarate not phenylalanine (iv, PEP/shikimate); Ribose 5-phosphate not aspartate; 3-Phosphoglycerate not glutamate.​

Option (D) P-ii; Q-i; R-iv; S-v incorrect: 3-Phosphoglycerate to serine (v), not phenylalanine (iv, PEP-derived).​

Correct answer: (A).

Amino acid biosynthesis relies on metabolic intermediates from glycolysis, TCA cycle, and pentose phosphate pathway as carbon backbones. This guide details key mappings for CSIR NET preparation.

Biosynthesis Pathways

Cells derive non-essential amino acids from central metabolism.

• α-Ketoglutarate family: Forms glutamate via glutamate dehydrogenase, extending to glutamine, proline, arginine.​

• Ribose 5-phosphate pathway: PRPP initiates histidine synthesis, unique among amino acids.​

• 3-Phosphoglycerate route: Leads to serine (then glycine, cysteine) through phosphorylated pathway enzymes.​

• PEP and shikimate: PEP drives aromatic amino acids like phenylalanine, tyrosine, tryptophan.​

CSIR NET Matching Strategy

Standard pairings include:

• α-Ketoglutarate → Glutamate

• Ribose 5-phosphate → Histidine

• 3-Phosphoglycerate → Serine

• Phosphoenolpyruvate → Phenylalanine.​

These reflect conserved pathways across organisms, vital for exam recall.​