Watson & Crick proposed a 3-dimensional secondary structure of DNA. In this DNA molecule, Monomners of DNA are held together by Phosphodiester linkage. This linkages are occured in 5' & 3' carbon atoms of Pentose sugar.

(a) C₄ carbon of the given sugar contains H and OH on the same configuration like C₄ carbon in L-Glyceraldehyde. Therefore the sugar is L-sugar.
(b) Because the H and OH on C₄ carbon are in the same configuration as the Hand OH on C₄ carbon in L-Glyceraldehyde

α - Helix:
In the a-helix sub-structure, the amino acids are arranged in a right handed helical (spiral) structure and are stabilised by the hydrogen bond between the carbonyl oxygen one amino acid (nth residue) with amino hydrogen of the fifth residue (n + 4^th residue).The side chains of the residues protrude, outside of the helix. Each turn of an a-helix contains about 3.6 residues and is about 5.4 Å long.The amino acid proline produces a kink in the helical structure and often called as a helix breaker due to its rigid cyclic structure.

α-D (+) glucophyranose

(i) Enzymes are naturally occurring simple or conjugated proteins which act as biological catalysts in living systems.
(ii) E.g. Carbonic anhydrase, Lactase, Sucrose

∴ Two dipeptides structures are possible from glycine and alanine. They are glycyl alanine and Alanyl glycine.

(i) Hormone is an organic substance (e.g. a peptide or a steroid) that is secreted by one tissue. It limits the blood stream and induces a physiological response (e.g. growth and metabolism) in other tissues. It is an intercellular signalling molecule.
(ii) e.g. Testosterone, Thyroxine, Estrogen, Insulin, Oxytocin etc.

Vitamins are classified into two groups based on their solubility in water or in fat.
(a) Fat soluble vitamins:
These vitamins absorbed best when taken with fatty food and are stored in fatty tissues and livers. These vitamins do not dissolve in water. Hence they are called fat soluble vitamins. Vitamin A, D, E & K are fatsoluble vitamins.
(b) Water soluble vitamins:
Vitamins B (B₁, B₂, B₃, B₅, B₆, B₇, B₉ & B12) and C are readily soluble in water. On the contrary to fat soluble vitamins, these can't be stored. The excess vitamins present will be excreted through urine and are not stored in our body. Hence, these two vitamins should be supplied regularly to our body.

i) Starch - Polysaccharide
ii) fructose - monosaccharide
iii) sucrose - oligosaccharides 
iv) lactose - oligosaccharides
iv) maltose - oligosaccharides

(i) Almost all carbohydrates are optically active as they contain one or more chiral carbons.
(ii) The number of optical isomers depends upon the number of chiral carbons (ie) 2ⁿ isomers, where n = total number of chiral carbons.
(iii) Glucose has \(4{ }^{\star} \)C; ∴ It has 2⁴ =16 isomers.

(i) Each protein has a unique three-dimensional structure formed by interactions such as disulphide bond, hydrogen bond, hydrophobic and electrostatic interactions. These interactions cain be disturbed when the protein is exposed to a higher temperature, certain chemicals such as urea, alteration of pH, ionic strength etc., It leads to the loss of the three-dimensional structure partially or completely. The process of a losing its higher order structure without losing the primary structure, is called denaturation. When a protein denatures, its biological function is also lost.
(ii) Since the primary structure is intact, this process can be reversed in certain proteins. This can happen spontaneously upon restoring the original conditions or with the help of special enzymes called cheperons (proteins that help proteins to fold correctly).
(iii) Example: coagulation of egg white by action of heat.

Hormone	Vitamin
Synthesized in animal bodies	Synthesised in plants
Produced in ductless (endocrine glands)	Have to be supplied in diet except (Vitamin D)
These are not stored in body but are continuously produced	These remain stored in the body to keep away diseases
Eg: Androgen, Estrogen, thyroxine etc.	Eg: Vitamin A (Retinol) Vitamin C (Ascorbic acid)

i) Rickets - Vitamin - D (Cholecalciferol - (D₃) Ergocalciferol - (D₂)
ii) Scurvy (bleeding gums) - vitamin - C (Ascorbic acid)

(i) Lipids ate the integral component of cell membrane. They are necessary of structural integrity of the cell.
(ii) The main function of triglycerides in animals is as an energy reserve. They yield more energy than carbohydrates and proteins.
(iii) They act as protective coating in aquatic organisms.
(iv) Lipids of connective tissue give protection to internal organs.
(v) Lipids help in the absorption and transport of fat soluble vitamins.
(vi) They are essential for activation of enzymes such as lipases.
(vii) Lipids act as emulsifier in fat metabolism.

(i) Ribonucleic acids are similar to DNA. Cells contain up to eight times high quantity of RNA than DNA. RNA is found in large amount in the cytoplasm and a lesser amount in the nucleus. In the cytoplasm it is mainly found in ribosomes and in the nucleus, it is found in nucleolus.
(ii) RNA molecules are classified according to their structure and function into three major types
i. Ribosomal RNA (rRNA)
ii. Messenger RNA (mRNA)
iii. Transfer RNA (tRNA)
rRNA:
rRNA is mainly found in cytoplasm and in ribosomes, which contain 60% RNA and 40% protein. Ribosomes are the sites at which protein synthesis takes place.
tRNA:
tRNA molecules have lowest molecular weight of all nucleic acids. They consist of 73 - 94 nucleotides in a single chain. The function of tRNA is to carry amino acids to the sites of protein synthesis on ribosomes.
mRNA:
mRNA is present in small quantity and very short lived. They are single stranded, and their synthesis takes place on DNA. The synthesis of mRNA from DNA strand is called transcription. mRNA carries genetic information from DNA to the ribosomes for protein synthesis. This process is known as translation.