DNA
Within each chromosome lies a gigantic molecule
of chemical known as deoxyribonucleic acid or DNA
in short. The DNA is very tightly packed like a spring.
Each chromosome can be regarded as a very long piece
of DNA which if fully stretched would be 2 metres
long!
How
does a DNA molecule look like? The structure of the
DNA molecule was first discovered by two scientists
known as James Watson and Francis Crick in 1953. It
looks like a very long twisted ladder known as a double
helix (See diagram)
The
two sides of the ladder are made of sugar phosphate.
The rungs of the ladder are the most important because
they give the cell its information. Each rung is split
into half, and each half of the rung is made of a
nitrogenous chemical, which can either be adenine,
guanine, cytosine or thymine. They are typically referred
simply as A, G, C or T. These chemicals join in the
middle and these bases always occur in pairs. A always
joins to T, and C always joins to G. A base pair or
bp in short refers to either a pair of A and T or
a pair of G and C
A
sugar and phosphate (found on the side of the ladder)
and one nitrogenous base (found on the rungs of the
ladder) is called a nucleotide. Each strand of the
double helix therefore contains many nucleotides.
