Altering DNA base sequence can alter protein structure - AL only (3.8.1)
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A gene mutation is a change in the sequence of bases in DNA.
Mutations can occur spontaneously during DNA replication and may affect the amino acid sequence of the resulting protein. Some mutations have no effect, while others may be beneficial or harmful depending on where they occur in the genome.
Mutations can also occur due to mutagenic agents, such as radiation, UV light, or certain chemicals, which can alter the DNA.
Substitution is a mutation where one nucleotide is replaced with another. This could lead to a variety of different effects.
With silent mutations, the degenerate nature of DNA means there can be a change in the triplet code with no change to the amino acid.
Addition and deletion mutations occur when a base is added or removed. The number of bases added or removed impacts the significance of the mutation.
If the number of bases added or deleted is not a multiple of three, this causes a frame shift, and every amino acid after the mutation could be altered.
If a multiple of three bases is added or deleted, one or more amino acids will be added or deleted, resulting in a single point mutation. This alters the primary structure at that point in the chain, but has no impact on the remainder of the coded amino acids.
Duplication mutations occur when one or more bases are duplicated. The impact of duplication mutation is the same as addition mutation but the causes vary.
Some mutations involve moving a section of DNA.
Inversion mutations are when a section of DNA is separated and rejoins in the same place, but in the reverse order. This would not cause a frame shift, but would alter the protein folding, as the inverted section would code for different amino acids.
Translocation – a section of DNA is separated and rejoins on a different chromosome. Translocations have a significant impact on phenotype as they affect two different areas of the genome. Translocations tend to affect how genes are expressed as well as the sequence of amino acids in a particular protein.
Some different mutations and their impact on the coding of the primary structure are illustrated below. Note the frame shifts caused where the addition, deletion and insertion examples are not multiples of three.
Many types of mutations, such as addition, deletion, duplication and translocation can cause a frame shift. A frame shift causes all subsequent triplet codes past the point of mutation to be read incorrectly. This significantly impacts the protein produced.
All mutation types have the potential to introduce a stop codon, thereby shortening the amino acid chain and leading to an ineffective protein.