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What is DNA?

Our genetic material is made of DNA (deoxyribonucleic acid).

dna-double-helix

A molecule of DNA resembles a spiral ladder, where the sides are made of sugar (deoxyribose) and phosphate and each rung is made of a pair of chemical bases weakly bonded together.

There are four bases present in DNA; adenine (A), thymine (T), cytosine (C) and guanine (G). A always pairs with T to form a rung (base pair) and C always pairs with G.

bases present in DNA

The weak bonds between the bases mean that the DNA molecule can be easily separated into two strands. Each strand can act as a template for the other as it is known which base has to pair with which. This complementarity allows the cell to make a copy of its DNA before it divides (DNA replication) and also underpins many of the techniques used in the lab to manipulate DNA.

separation-of-dna-base-pairs

DNA can be a very long molecule. The DNA from a single human cell stretched out would reach approximately six feet (180cm) in length. For that reason, it has to be packed up efficiently to fit into the cell nucleus. This process, called supercoiling is highly regulated and involves the DNA wrapping itself around proteins called histones. The DNA within a cell's nucleus is thereby folded and packaged up into 46 molecules called chromosomes. 

Did you know?
All of the molecular genetic tests that are carried out in the clinical genetics laboratory rely upon DNA's ability to separate into two strands and the specificity of base pairs (A always pairing with T and C always pairing with G)

 

Find out more:

A PDF document

DNA

Use this factsheet to provide an introduction to the properties of deoxyribonucleic acid (DNA).

 

A PDF document

Variations in DNA and their effects

Use this factsheet to provide an overview of DNA variations and their effects on the individual.