A point mutation is a change in a single base in one DNA strand. Some people include insertions and deletions of bases as point mutations, but I think they should be treated separately.
Point mutations are also referred to as single nucleotide polymorphisms or SNPs for short. These can have a number of different effects: Note that the SNPs that are usually considered of biological importance are those occurring within the promoter or coding regions of a gene. A point mutation in 'junk' DNA would have no effect, at least none that we know of.
Missense - changes the codon so that a different amino acid is inserted when the gene is translated. Sometimes the changed codon still codes for the same amino acid in which case the protein remains the same. This is known as a 'silent' mutation. At other times, the mutated codon changes the amino acid to a different one but its chemical properties are so similar that the translated protein has the same function. This is known as a 'conservative' point mutation because the protein function is conserved.
If the SNP causes a codon change resulting in a chemically different (e.g., hydrophobic for hydrophilic) amino acid, the mutation is known as non-conservative because the protein structure is changed and the function may be altered.
Nonsense Mutation - this type of point mutation creates a codon that does not code for an amino acid but rather a STOP signal that terminates protein synthesis. Depending on where the STOP codon is, the resulting protein may be be so truncated as to be totally inactive.
Coding vs Noncoding Mutations - many genes have an upstream promoter, repressor or enhancer region that controls gene expression. A point mutation in this region can change the DNA sequence that is recognized by a promoter protein and alter gene expression. The protein is normal but the level of expression is affected. Point mutations can also occur in introns, the DNA sequences between the exons in many genes. The introns are required for correct splicing of the exons and a point mutation in an intron can alter the splicing and change the structure of the resulting protein.
Sourceshttps://en.wikipedia.org/wiki/Point_mutation
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