Substitution of Bases

A mutation may arise where one nucleotide base is substituted for another.For example if in the template strand triplet GTC cytosine is substituted with guanine, the triplet code will read GTG and code for histidine rather than glutamine. This is called a base substitution and the effect will depend on the role the amino acid plays in the protein.Histidine and glutamine have different structures and properties. If the amino acid replaced is in the active site of an enzyme it may cause a change of function of enzyme by altering the shape of the active site, or the enzyme may not function at all.On the other hand the base substitution may cause no discernable change. This is known as a silent mutation.A base substitution may result in the same amino acid being incorporated into the polypeptide chain.For example if GTC was changed to GTT since both triplets code for glutamine there would be no change in the amino acid sequence.