There are two distinct types of nucleic acid: deoxyribonucleic acid
(abbreviated to DNA) and ribonucleic acid (RNA).
You will undoubtedly meet these molecules again and again as you study biology! They are
large polymers (chains) composed of smaller sub-units known as nucleotides. Each
nucleotide consists of a sugar, a phosphate group and a base (this is a chemical group
that contains nitrogen). DNA is formed from two chains side by side, while RNA is a single
DNA stores genetic information, while RNA in its several forms uses that
information to manufacture specific proteins. Directly and indirectly, these molecules
have a significant influence on just about every aspect of cellular activity and general
Deoxyribonucleic acid (DNA)
DNA is a large macromolecule (large, that is, in relation to other molecules!)
in the shape of a double helix.
If the DNA molecule can be imagined as a ladder that has become rather
twisted, then the sugars and phosphate groups of the nucleotides are strongly bonded
together to form the sides of the ladder, whilst the bases are weakly joined by hydrogen
bonds to each other in pairs to form the 'rungs'. This elegant arrangement allows copies
of the molecule to be made - the two strands separate and each then provides a template
for a new second strand to be built alonside it. The copying process is called
replication, and occurs without any of the genetic information being lost. (We shall take
a closer look at cell division in a later Gallery.)
DNA is mainly located in the nucleus (central compartment) of a cell,
distributed between 46 structures called chromosomes.
(There is in addition a small amount of DNA associated with other parts of the cell, as we
shall see later.)
DNA holds all the instructions or genes
for cell activity and it governs everything from cell growth to eye colour.
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