Soon after Mendel's work scientists came to know that all the activies of the living organisms are controlled by the single
structural and functional unit called as "Cell". Cell has a central controlling body called as
nucleus. The nucleus can be described as " The Brain" of the cell. The nucleus contains
chromosomes which are responsible for the transfer of heredity.Chromosomes has several factors on them which are called as "genes".
Genes are tightly coiled to form a thin thread like structure called DNA ( DeoxyRibonuclic Acid) DNA is found in the nucleus. DNA is the longest and the complex biomolecule.
It comprises of the chain of nucleotides link together to form a polynucleotide
Each nucleotide is composed of
i) pentose suger (Ribose)
ii) phosphate group
iii) one of the nitrogen bases attached to ribose suger
The nitrogenous bases are of two types
Purines such as
Adenine(A) and
Guanine (G)
Pyrimedines such as
Thymine(T) and
Cytosine(C)