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Option : (d) hydrogen bond

Option : (d) Watson and Crick

Adenine and guanine.

These are nitrogenous bases. 

Amino acids are bi-functional compounds containing both carboxylic acid group (-COOH) and basic amino group (-NH₂). They are building blocks of proteins. They are linked together by peptide bond. due to the formation of zwitter ion it is amphoteric in nature.

In a DNA, a purine always pairs with a pyrimidine i.e. adenine pairs with thymine (A = T) and guanine with cytosine (G = C). This is called a complementary pairing.

The structure differences between DNA and RNA are as follows:

The functional difference between DNA and RNA are as follows:

(D) Globulin

1. Conjugated proteins consist of a simple protein attached with some non-protein substance. The non-protein group is called prosthetic group. 

2. The conjugated protein functions in interaction with other chemical group whereas simple proteins contain only amino acids and no other chemical group attached to it. 

3. Example of conjugated protein is haemoglobin. Globin is the protein and iron containing pigment and haem is the prosthetic group.

Glycoprotein

Inhibitor closely resembles the substrate in its molecular structure and inhibits the enzyme activity. 

E.g., inhibition of succinic dehydrogenase by malonate.

Classification of enzymes : 

Oxidoreductase/dehydrogenases : Catalyse oxidoreduction between 2 substrates. 

Transferases : Catalyse transfer of a group between a pair of substrates. 

Hydrolases : Catalyse hydrolysis of ester, ether, peptide, glycosidic, C-C, P-N bonds. 

Lyases : Catalyse removal of groups from substrates by mechanisms other than hydrolysis. 

Isomerases : Catalyse inter-conversion of optical, geometric or positional isomers. 

Ligases : Catalyse linking together of 2 compounds. 

Cofactors : Non-protein constituents found to the enzyme to make it catalytically active. Protein portion of enzyme is called apoenzyme. 

• Prosthetic groups : Are organic compounds tightly bound to apoenzyme. E.g., haem in peroxydase and catalase. 

• Co-enzymes : Organic compounds which has transient association with enzyme. E.g., NAD, NADP. 

• Metal ions : Required for enzyme activity. Form coordination bond with side chains at active site and with substrate. E.g., zinc is a co-factor for enzyme carboxypeptidase.

Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) is called Nucleic acids.

Oils are unsaturated lipids, hence have lower melting points.

Nitrogen an element found in proteins but not in lipids and carbohydrates.

RNA has uracil instead of thymine.

Lowers the activation energy of reaction. 

Are the energy currency of cell.

The intercellular ground substance is Collagen.

Option : (b) the acidic group -N⁺H₃ and the basic group COO^-

The α-carbon has 4 substituted groups occupying the 4 valency positions : - H, -COOH, -NH₂ and -R group.

a. The three main components of any cell are: 

Cell membrane, Cytoplasm, Nucleus. 

b. The components present in both plant and animal cells are:

Endoplasmic reticulum, ribosomes, golgi apparatus, lysosomes, mitochondria, vacuoles. 

c. The components present in plant cell and not in animal cell: 

Cell wall and plastids. 

d. The components present in animal cell and not in plant cell:

Cilia and flagella.

a. When there is high level of cholesterol in the blood, the cholesterol builds up on the walls of arteries causing a condition called atherosclerosis (a form of heart disease). 

b. Because of this the arteries are narrowed and the blood flow to the heart is slowed down. 

c. The blood carries oxygen to the heart, but because of this condition enough blood and oxygen does not reach to the heart and causes heart diseases. 

d. If the condition increases, the supply of oxygen and blood is completely cut off to the heart and this can lead to heart attack.

The role of each component of a cell is as follows: 

a. Cell membrane: Cell membrane separates the cytoplasmic contents from external environment. 

b. Cytoplasm: Site for metabolic activities and organelles. 

c. Nucleus: It is the control center of the cell. Genetic material is present in the nucleus. 

d. Endoplasmic reticulum: It produces, processes and transports proteins and lipids. 

e. Ribosomes: Ribosome is the site for protein synthesis. 

f. Golgi apparatus: It is involved in modifying, sorting and packing of proteins for secretion. It also transports lipids around the cell. 

g. Lysosomes: It is involved in digestion of worn out organelles and waste removal.

h. Mitochondria: It is responsible for production of energy. 

i. Vacuoles: It has various functions like storage, waste disposal, protection and growth. 

j. Cell wall: It provides strength and support to the cell. 

k. Plastids: They are responsible for production and storage of food. It also contains photosynthetic pigments (Chloroplasts). 

l. Cilia and flagella: Help in motility

Lipids:

Lipids are a group of heterogeneous compounds like fats, oils, steroids, waxes, etc. They are macro-biomolecules. These are group of substances with greasy consistency with long hydrocarbon chain containing carbon, hydrogen and oxygen. 

Lipids are classified into: 

1. Saturated fatty acids: They contain single chain of carbon atoms with single bonds. 

E.g. Palmitic acid, stearic acid 

2. Unsaturated fatty acids: 

They contain one or more double bonds between the carbon atoms of the hydrocarbon chain. 

a. Simple lipids: These are esters of fatty acids with various alcohols. 

E.g. Fats, wax

b. Compound lipids: 

These are ester of fatty acids containing other groups like phosphate (Phospholipids), sugar (glycolipids), etc. 

E.g. Lecithin 

c. Sterols: 

They are derived lipids. They are composed of fused hydrocarbon rings (steroid nucleus) and a long hydrocarbon side chain. 

E.g. Cholesterol, phytosterols.

1. The word carbohydrates mean ‘hydrates of carbon’. 

2. They are also called saccharides. 

3. They are biomolecules made from just three elements: carbon, hydrogen and oxygen with the general formula C_x (H₂O)_y. 

4. They contain hydrogen and oxygen in the same ratio as in water (2:1). 

5. Carbohydrates can be broken down (oxidized) to release energy.

(D) polysaccharide

a. Starch: 

1. Natural Sources: Cereals (wheat, maize, rice), root vegetables (potato, cassava etc.) 

2. Structural units: Starch consist of two types of molecules – Amylose and amylopectin. 

3. Functions: It acts as a reserve food and supply energy.

b. Cellulose: 

1. Natural sources: Plant fibers (cotton, flax, hemp, jute, etc.), wood. 

2. Structural units: It is made from p glucose molecules. 

3. Functions: It in a major component of cell wall. It provides structural support. 

c. Glycogen: 

1. Natural sources:

Fruits, starchy vegetables, whole grain foods. 

2. Structural units: 

It consists of linear chains of glucose residues. The glucose is linked linearly by a (1 → 4) glycosidic bonds and branches are linked to the linear chain by a (1 → 6) glycosidic bonds. 

3. Functions: 

It is stored in liver and muscles and it readily provides energy when the blood glucose level decreases.

Oligosaccharides: 

a. A carbohydrate polymer comprising of two to six monosaccharide molecules is called oligosaccharide. 

b. They are linked together by glycosidic bond. 

c. They are classified on the basis of monosaccharide units: 

Disaccharides: These are the sugars containing two monosaccharide units and can be further hydrolysed into smaller components. 

E.g.: Sucrose, maltose, lactose, etc. 

Trisaccharides: These contain three monomers. 

E.g. Raffmose.

Tetrasaccharides: These contain four monomers. 

E.g.: Stachyose.

Glycosidic bond: 

a. Glycosidic bond is a covalent bond that forms a linkage between two monosaccharides by a dehydration reaction.

b. It is formed when a hydroxyl group of one sugar reacts with the anomeric carbon of the other. 

c. Glycosidic bonds are readily hydrolyzed by acid but resist cleavage by base. 

d. There are two types of glycosidic bonds: aglycosidic bond and P-glycosidic bond.

Reactions of glucose that cannot be explained by open chain structure : 

(i) Glucose gives the characteristic reaction of alcohols and carbonyl group (aldehydes and ketones). However it does not form addition compound with ammonia and sodium bisulphite and does not respond to 2, 4-DNP test and Schiffs test. 

(ii) The penta-acetate of glucose does not react with hydroxyl amine indicating the absence of free - CHO group.

(a) Both A and R are correct and R is the correct explanation of A.