Question

(a) Mention any two bases present in DNA.

(b) Which component of starch is an unbranched chain polymer of \( \alpha \)-D-(+) glucose ? Write its one characteristic feature.

(c) Write the name of the linkage present between amino acids. How is it represented ?

Hint:

Amylose is the linear part of starch. Amino acids are joined by the peptide linkage, -CO-NH-.

Answer 1

Step 1: Part (a), name the DNA bases.
DNA holds four nitrogenous bases: adenine (A), guanine (G), cytosine (C) and thymine (T).
Adenine and guanine are purines. Cytosine and thymine are pyrimidines.
Any two of these is correct, for example adenine and guanine.

Step 2: Part (b), find the starch component.
Starch is a mixture of two polysaccharides, amylose and amylopectin.
Amylose is the unbranched, linear chain. Amylopectin is branched.
So the answer is amylose.
Its characteristic feature: the glucose units are joined by \( \mathrm{C_1-C_4} \) \( \alpha \)-glycosidic linkages in a long chain.

Step 3: Part (c), name the linkage in proteins.
The carboxyl group of one amino acid joins the amino group of the next one, and a water molecule is lost.
The amide bond formed is called a peptide linkage.
It is written as \( \mathrm{-CO-NH-} \).

Final Answer:
(a) Adenine and guanine (or any two of A, G, C, T).
(b) Amylose; it has \( \mathrm{C_1-C_4} \) \( \alpha \)-glycosidic links in an unbranched chain.
(c) Peptide linkage, \( \mathrm{-CO-NH-} \).