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Nucleic acids

DNA (21K bytes)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 chain.

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 metabolism.

Deoxyribonucleic acid (DNA)

DNA molecule (19K bytes)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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