DNA - Mutations (GCSE Biology)
Mutations
Mutation
Mutations are rare, random changes in the base sequence of DNA that can be inherited. They can lead to alterations in the polypeptide chain and so can lead to non-functional proteins. The majority of mutations don’t cause profound changes in proteins. This is for many reasons.
- The triplet code is degenerate. This means that in many circumstances, one base may change, but the amino acid coded for by the codon will not. This means that the right protein will still form.
- Slight changes may not alter the function of the protein. The protein may only change slightly, therefore the functionality may not actually be altered.
However, in cases such as enzymes, even small mutations can lead to changes in the active site. This could easily make them non-functional.
This could also be problematic in DNA that codes for structural proteins. If a sequence for a key structural protein is altered, it may lead to big problems in the body.
Mutations in non-coding DNA can also cause problems as they can interfere with and stop the transcription of DNA. Hence, they can alter how genes are expressed.
Mutations can occur in three ways:
- Deletion – A deletion mutation involves losing a base in the sequence. This can often lead to a frame shift mutation, which can cause great issues.
- Insertion – A base may be inserted into the sequence.
- Substitution – A base is substituted into the sequence instead of another.
Incidence of Mutations
- The incidence of mutations can be increased by exposure to ionising radiation. For example, gamma rays, x-rays and ultraviolet rays.
- The incidence of mutations can also be increased by some chemical mutagens. For example, chemicals in tobacco.
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