Read the passage carefully and answer the questions:

Optically active polyhydroxy aldehydes or ketones or molecules which provide such units on hydrolysis are called carbohydrates. They can be broadly classified as monosaccharides, disaccharides and polysaccharides depending on their behavior towards hydrolysis. They are also classified as reducing or non reducing sugars. Another class of biomolecules is proteins which are polymers of twenty different amino acids linked by peptide bonds. Amino acids can be classified as acidic, basic or neutral depending on the relative number of amino and carboxyl groups in their molecule. The essential amino acids cannot be synthesized by our body and hence must be provided through diet. Nucleic acids are the polymers of nucleotides which in turn consist of a base, pentose sugar and phosphate. There are two types of nucleic acids namely, DNA and RNA which differ in the composition of sugar and a base.

The side chain (R group) present in the "Aspartic Acid" amino acid is

$HOOC-CH_{2-}$

The correct answer is Option (2) → $HOOC-CH_{2-}$ **

Aspartic acid is an acidic amino acid because its side chain contains an additional carboxyl group (–COOH).

The general structure of amino acids is:

NH₂ – CH(R) – COOH

For Aspartic Acid, the side chain (R group) is:

R = –CH₂ – COOH

Thus it is written as:

HOOC – CH₂ –

Because of the extra carboxyl group, aspartic acid behaves as an acidic amino acid.

Option-wise Explanation

Option 1: H₃C – S – CH₂ – CH₂ –

Incorrect. This side chain corresponds to methionine, a sulfur-containing amino acid.

Option 2: HOOC – CH₂ –

Correct. This is the side chain of aspartic acid.

Option 3: HOOC – CH₂ – CH₂ –

Incorrect. This corresponds to glutamic acid, which has a longer side chain.

Option 4: HO – CH₂ –

Incorrect. This is the side chain of serine, a hydroxy amino acid.