How does DNA repair itself?

Most DNA mutations occur when your cells divide. But your DNA is also under constant attack from other chemicals in your cells. Fortunately, your cells have a very efficient DNA repair system which is constantly scanning your DNA. Without these DNA repair enzymes, your cells would soon accumulate too much damage to survive. There are two main repair systems: one for removing and replacing a single base-pair mutation, and another for removing long stretches of unwanted, extra base pairs.

Back to top

Enlarge

The protein BRCA1 helps repair DNA.

How do mutations affect proteins?

Very occasionally, a DNA mutation occurs in a gene, changing its RNA molecule and sometimes affecting the protein it codes for. The RNA code uses four chemical 'letters' (bases), known as A, C, U, and G, in groups of three. Adding, removing or changing just one base can have a drastic effect on a gene, just as changing one letter in a sentence of three-letter words can alter its meaning.

Back to top

Play

The RNA code.

How can DNA bases change?

The DNA code CCA GCA CAC CAA tells the cell to add the amino acids proline, alanine, histidine and glutamine to the protein it is making. If just one of the DNA bases is changed, a different amino acid may be substituted. Adding or removing a base can have an even more drastic effect, as all the code that follows is disrupted.

Back to top

Play

Changing a gene.

How is DNA like a sentence?

Imagine changing just one letter in the sentence 'THE CAR WAS RED'. This can change its whole meaning. Adding or removing a letter from the sentence can have an even more drastic effect since all the words that follow are disrupted, making nonsense of the sentence. Similarly, changing, adding or removing a single letter in the DNA code for a gene can affect the protein it makes.

Back to top

'Junk' DNA?

You have 6000 million base pairs of DNA in almost every one of your cells, but only about 3% of it makes up genes. Of the remaining 97% some helps keep the DNA bound together. Scientists used to call this ‘junk DNA’. Now they have found that much non-coding DNA has essential roles such as controlling the activity of genes. There is much yet to discover about the role of non-coding DNA.

Back to top

Play

Only 3 per cent of your DNA makes up genes.

 

Principal Funder:

Wellcome trust

Major Sponsors:

GlaxoSmithKline life technologies