Biomolecules Test - 9

Vitamin A keeps eyes in good health. Deficiency of Vitamin A causes Night Blindness.

Complete hydrolysis of RNA yields a pentose sugar, phosphoric acid and nitrogen containing heterocyclic compounds (called bases). In RNA molecule, the sugar moiety is β-D-ribose.

DNA contains four bases viz. adenine (A), guanine (G), cytosine (C) and thymine (T). RNA also contains four bases, the first three bases are same as in DNA but the fourth one is uracil (U).

A unit formed by the attachment of a base to 1′ position of sugar is known as nucleoside. In nucleosides, the sugar carbons are numbered as 1′, 2′, 3′, etc. in order to distinguish these from the bases.

When nucleoside is linked to phosphoric acid at 5ꞌ – position of sugar moiety, we get a nucleotide.

When nucleoside is linked to phosphoric acid at 5′-position of sugar moiety, we get a nucleotide and nucleotides are joined by a phosphodiester bond between 5′ and 3′ carbon atoms of the pentose sugar.

Two nucleic acid chains are wound about each other and held together by hydrogen bonds between pairs of bases. The two strands are complementary to each other because the hydrogen bonds are formed between specific pairs of bases. Adenine forms hydrogen bonds with thymine whereas cytosine forms hydrogen bonds with guanine. So base pair in a double helix of DNA is A-T.

A sequence of bases on DNA is unique for a person and information regarding this is called DNA fingerprinting. It is same for every cell and cannot be altered by any known treatment.

Proteins may have one or more polypeptide chains. Each polypeptide in a protein has amino acids linked with each other in a specific sequence and it is this sequence of amino acids that is said to be the primary structure of that protein. Thus the most appropriate structure for knowing about the sequence of nucleotides in the DNA chain is its primary structure.

Curdling of milk is caused due to the formation of lactic acid by the bacteria present in milk. Milk contains proteins. When a protein in its native form, is subjected to physical change like change in temperature or chemical change like change in pH, the hydrogen bonds are disturbed. Due to this, globules unfold and helix get uncoiled and protein loses its biological activity. This is called denaturation of protein.