Mutations

Since every letter in a gene is part of a word in the recipe book, it’s important that every letter is in the correct place. A mutation changes the order of the letters in the DNA sequence.

Why does this matter?

This is important as it can change the protein that is made. If we changed the C in the word CAT to a T, the sentence: “the cat sat on the mat” wouldn’t make much sense any more – TAT is still a word, but it’s not the right word for this sentence. In much the same way if we change one of the nucleotides in a codon – the word is altered and we’ll get the wrong amino acid being added to the protein.
Or, if the word gets altered to the special stop codon, the protein will stop being made and be too short. This shortening is called a truncation.

Silent mutations

Any change to the DNA sequence is a mutation, however not all mutations cause a change to the amino acid sequence of a protein.  

Some amino acids casino have several different codons representing them – for example the codon for glycine can be GGT, GGC, GGA or GGG – this means if the last letter is changed due to a mutation in the DNA it doesn’t matter; the meaning of the word is still glycine. This kind of mutation is called a silent mutation.
Other silent mutations can occur when DNA is mutated outside of a gene, such as in a region that doesn’t do anything (remember not all DNA is part of a gene). 		  Double helix with single base pair mutation highlighted

What causes mutations?

There are two main ways that DNA may be mutated.

  • Enviromental factors, such as chemicals (which are called mutagens if they affect DNA), viruses (e.g. the human papillomavirus that can cause cervical cancer) and radiation (e.g. UV light from the sun) can all damage DNA
  • Mistakes can occur when a cell copies its DNA whilst getting ready for cell division, most of the time these mistakes are corrected by proteins in your cells, but sometimes they are missed, and the mutation is passed on to the daughter cell. 

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