Nucleic Acids- Mutations

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What is a mutation?

A mutation is a heritable change in the DNA. This may be due to a base being substituted or deleted, or due to larger mutations such as chromosomes fusing together.

What is a missense mutation?

A missense mutation is a mutation in which an amino acid changes to a different one. There are two types of missense mutations: conservative and non-conservative. Conservative missense mutations are missense mutations in which the new amino acid has similar properties to the old one (e.g. both of them might be basic), allowing the protein to function as before. In non-conservative missense mutations, however, the new amino acid is so different to the old one that the protein can no longer perform its original function.

What is a nonsense mutation?

A nonsense mutation is one in which a codon coding for an amino acid is changed to a stop codon. This creates a polypeptide that is much shorter and usually non-functional.

What is a silent mutation?

A silent mutation is a mutation in which the sequence of bases on the DNA changes, but the amino acids do not. This can occur because the genetic code is degenerate (i.e. multiple different codons can code for the same amino acid).

How does base tautomerisation impact on DNA sequence fidelity?

Bases can exist in several different tautomers, in which the double bonds and hydrogen atoms are located in different positions. Some of these tautomers may be able to pair with bases that they normally would not be able to pair with (though purines will still pair with pyrimidines and vice-versa). This anomalous base-pairing may cause an incorrect base to be inserted during DNA replication or transcription.