BIO BOTANY [5 Mark each]

Compare DNA with RNA:

DNA	RNA
1. Deoxyribose sugar is present	1. Ribose sugar is present
2. Thymine is present	2. Uracil is present
3. More stable	3. Less stable
4. Double stranded	4. Single stranded
5. Types: A – DNA, B – DNA, Z – DNA	5. Type: mRNA, tRNA, rRNA
6. Genetic material for most of living organism except few viruses	6. Genetic material for few viruses only

The various features of different forms of DNA:

S. No	Feature	B-DNA	A-DNA	Z-DNA
1	Type of helix	Right-handed	Right-handed	Left-handed
2	Helical diameter (nm)	2.37	2.55	1.84
3	Rise per base pair (nm)	0.34	0.29	0.37
4	Distance per complete turn (pitch) (nm)	3.4	3.2	4.5
5	Number of base pairs per complete turn	10	11	12
6	Topology of major groove	Wide, deep	Narrow, deep	Flat
7	Topology of minor groove	Narrow, shallow	Broad, shallow	Narrow, deep

Many enzymes require non – protein components called co – factors for their efficient activity. Co – factors may vary from simple inorganic ions to complex organic molecules.
They are of three types:

1. Inorganic ions, prosthetic groups and coenzymes.
2. Holoenzyme – active enzyme with its non – protein component.
3. Apoenzyme – the inactive enzyme without its non – protein component.

Inorganic ions help to increase the rate of reaction catalysed by enzymes. Example: Salivary amylase activity is increased in the presence of chloride ions. Prosthetic groups are organic molecules that assist in catalytic function of an enzyme. Flavin adenine dinucleotide (FAD) contains riboflavin(vit B2), the function of which is to accept hydrogen. ‘Haem’ is an iron – containing prosthetic group with an iron atom at its centre. Coenzymes are organic compounds which act as cofactors but do not remain attached to the enzyme. The essential chemical components of many coenzymes are vitamins. Eg. NAD, NADP, Coenzyme A, ATP.

Lock and Key Mechanism of Enzyme: In a enzyme catalysed reaction, the starting substance is the substrate. It is converted to the product. The substrate binds to the specially formed pocket in the enzyme – the active site, this is called lock and key mechanism of enzyme action. As the enzyme and substrate form a ES complex, the substrate is raised in energy to a transition state and then breaks down into products plus unchanged enzyme.

1. Hydrogen Bond: It is formed between some hydrogen atoms of oxygen and nitrogen in polypeptide chain. The hydrogen atoms have a small positive charge and oxygen and nitrogen have small negative charge. Opposite charges attract to form hydrogen bonds. Though these bonds are weak, large number of them maintains the molecule in 3D shape.

2. Ionic Bond: It is formed between any charged groups that are not joined together by peptide bond. It is stronger than hydrogen bond and can be broken by changes in pH and temperature. 3. Disulfide Bond: Some amino acids like cysteine and methionine have sulphur. These form disulphide bridge between sulphur atoms and amino acids. 4. Hydrophobic Bond: This bond helps some protein to maintain structure. When globular proteins are in solution, their hydrophobic groups point inwards away from water.

Flow Chart depicting the Carbohydrate Classification:

The primary structure is linear arrangement of amino acids in a polypeptide chain. Secondary structure arises when various functional groups are exposed on outer surface of the molecular interaction by forming hydrogen bonds. This causes the amino acid chain to twist into coiled configuration called α – helix or to fold into a flat β – pleated sheets.

Tertiary protein structure arises when the secondary level proteins fold into globular structure called domains. Quaternary protein structure may be assumed by some complex proteins in which more than one polypeptide forms a large multiunit protein. The individual polypeptide chains of the protein are called subunits and the active protein itself is called a multimer.

The primary structure is linear arrangement of amino acids in a polypeptide chain. Secondary structure arises when various functional groups are exposed on outer surface of the molecular interaction by forming hydrogen bonds. This causes the amino acid chain to twist into coiled configuration called α – helix or to fold into a flat β – pleated sheets.

Tertiary protein structure arises when the secondary level proteins fold into globular structure called domains. Quaternary protein structure may be assumed by some complex proteins in which more than one polypeptide forms a large multiunit protein. The individual polypeptide chains of the protein are called subunits and the active protein itself is called a multimer.