The control of gene expression (AQA A2 Biology) PART 1 of 8 TOPICS
Alternation of the sequence of bases in DNA can alter the structure of proteins:
Gene mutations might arise during DNA replication. The types of mutations include:
- Addition: This is where a base is added in between two bases. So if a base sequence was ATCGGA, addition of a base may cause ATA This causes a frame shift to the right.
- Deletion: This is where a base is deleted from the sequence. So if a base sequence was ATCGGA, deletion may cause ATGGA. This causes a frame shift to the left.
- Substitution: This is where a base is swapped for another base. So if a base sequence was ATCGGA, substitution may cause ATCTGA.
- Inversion: This is where the base sequence is inverted. So if a base sequence was ATCGGA, inversion may cause AGGCTA.
- Duplication: This where one or more bases is repeated. So if a base sequence was ATCGGA, duplication may cause ATT This causes a frame shift to the right.
- Translocation: This is where the base sequence is moved on to a different locus on the same chromosome or onto a whole new chromosome.
Gene mutations occur spontaneously but the rate of mutation is increased by mutagenic agents. These include x-rays and other ionising radiation, tar in cigarettes and radioactive isotopes of elements.
Mutations can result in a different amino acid sequence in the encoded polypeptide. The mutations that result in a different primary structure are addition and deletion. A change in the primary structure causes a change in the tertiary structure and could make a non-functional protein. Substitution is least likely to cause a mutation as the genetic code is degenerate i.e. more than one triplet can code for the same amino acid.