Molecular Genetics consists of chromosomes, deoxyribonucleic acid ( DNA) and genes. As well as the interactions among three major molecules (DNA, RNA ribonucleic acid and protein). An introduction to molecular genetics is presented as every nucleus of a human cell contains 46 chromosomes arranged in 23 pairs, 22 autosomes and two sex chromosomes. A chromosomes is an extremely long strand of supercoiled DNA bonded with protein molecules called histomes, genes are parts of the chromosomes with a coding function: they are unique sequences that code for specific proteins.
Genes comprise only the minority of the DNA of a chromosome. The remaining great majority of DNA has no known function with the exception of specific areas of the chromosome that are known to be important for correct replication at chromosome termini( telomeres) or correct movement of chromosomes into daughter cells following cell division ( centromeres). The DNA molecule consists of two DNA chains coiled around each other to form a double helix. Each DNA strand has a backbone of 5-carbon sugar (deoxyribose) residues, which are linked by covalent phosphodiester bonds .
On each residue is a nitrogenous base either a pyrimidine ( cytosine [C], or thymine [T] or a purine ( adenine [A], or guanine [G]. The two DNA chain has a polarity determine by the orientation of the sugar-phosphate backbone.