17 Phenylalanine, a precursor of most of the phenolics in higher plants is a product of which one of the following pathways?
(1) Shikimic acid pathway
(2) Malonic acid pathway
(3) Mevalonic acid pathway
(4) Methylerythritol pathway

Correct answer: (1) Shikimic acid pathway

Explanation:

• Phenylalanine, the precursor of most phenolic compounds in plants, is biosynthesized via the shikimic acid pathway.

• This pathway provides aromatic amino acids including phenylalanine, tyrosine, and tryptophan, essential for the production of many secondary metabolites.

• The malonic acid pathway is mostly related to fatty acid and polyketide synthesis, not phenylalanine biosynthesis.

• The mevalonic acid and methylerythritol phosphate (MEP) pathways are primarily involved in terpene and isoprenoid biosynthesis.

Option-wise:

• (1) Shikimic acid pathway — Correct.

• (2) Malonic acid pathway — Incorrect.

• (3) Mevalonic acid pathway — Incorrect.

• (4) Methylerythritol pathway — Incorrect.

Phenylalanine is synthesized through the shikimic acid pathway, producing aromatic amino acids crucial for the biosynthesis of phenolics and other plant secondary metabolites, differentiating it from terpene-related pathways like mevalonic acid and MEP.