Question

(a) What is peptide linkage?
(b) What type of bonds hold a DNA double helix together?
(c) Which one of the following is a polysaccharide?
(d) Give one example each for water-soluble vitamins and fat-soluble vitamins.

Hint:

- Peptide bonds form the backbone of proteins. - Hydrogen bonds are weak but critical for stabilizing the structure of DNA. - Starch is a major energy storage polysaccharide in plants. - Water-soluble vitamins are essential for metabolic processes, while fat-soluble vitamins are stored in fat tissues.

Answer 1

(a) A peptide linkage is a covalent bond that joins two amino acids through the carboxyl group (\(-COOH\)) of one amino acid and the amino group (\(-NH_2\)) of another, forming a \(-CONH-\) bond. This reaction results in the elimination of water (\(H_2O\)) and is known as a peptide bond. \[ \text{Amino acid 1} - \text{COOH} + \text{Amino acid 2} - \text{NH}_2 \rightarrow \text{Peptide bond} + H_2O \] 

(b) The DNA double helix is held together primarily by hydrogen bonding between the complementary nitrogenous bases. The adenine (A) base forms two hydrogen bonds with thymine (T), and guanine (G) forms three hydrogen bonds with cytosine (C). These hydrogen bonds are essential for the stability of the double helix structure of DNA. 

(c) The correct answer is starch. Starch is a polysaccharide composed of long chains of glucose molecules. It serves as a storage carbohydrate in plants. Sucrose and fructose are monosaccharides or disaccharides, and glucose is a monosaccharide. 

(d) - Water-soluble vitamins: Vitamin B and Vitamin C. - Fat-soluble vitamins: Vitamin A, D, E, K. These vitamins are classified based on their solubility, with water-soluble vitamins dissolving in water and fat-soluble vitamins dissolving in fats and oils.