Isoleucine is a derivative of which of the following acids?
heptanoic acid
hexanoic acid
pentanoic acid
butanoic acid
The correct answer and explanation is :
Correct Answer: Pentanoic Acid
Isoleucine is a derivative of pentanoic acid (also known as valeric acid). The structure of isoleucine consists of a five-carbon backbone, making it structurally related to pentanoic acid.
Explanation
Isoleucine is one of the essential amino acids, meaning that it cannot be synthesized by the human body and must be obtained from the diet. It belongs to the group of branched-chain amino acids (BCAAs) along with leucine and valine. The structural formula of isoleucine consists of an amino group (-NH₂), a carboxyl group (-COOH), and a side chain derived from pentanoic acid.
Relationship to Pentanoic Acid
- Basic Structure: Pentanoic acid (valeric acid) is a straight-chain carboxylic acid with five carbon atoms (C₅H₁₀O₂). Isoleucine retains this five-carbon backbone but has additional branching and functional groups.
- Side Chain in Isoleucine: The side chain of isoleucine is a β-methylbutyl group, which originates from the pentanoic acid backbone. This branching differentiates isoleucine from leucine, which has a different structural arrangement.
- Biochemical Pathway: In biosynthesis, isoleucine is derived from threonine via a metabolic pathway that involves keto-acid intermediates structurally related to pentanoic acid.
Why Not Other Acids?
- Heptanoic acid (C7H14O2): Too long; isoleucine has only five carbon atoms in its backbone.
- Hexanoic acid (C6H12O2): One carbon too many.
- Butanoic acid (C4H8O2): Too short; isoleucine has a five-carbon backbone.
Thus, pentanoic acid is the closest structural match to isoleucine.