substitutionsförändringar

Substitutionsförändringar, often translated as substitution mutations or base substitutions, are a type of point mutation where a single nucleotide base in a DNA sequence is replaced by another. This alteration can occur during DNA replication or through damage to the DNA molecule. There are two main categories of substitutions: transitions and transversions. Transitions involve the replacement of a purine with another purine (adenine with guanine, or guanine with adenine) or a pyrimidine with another pyrimidine (cytosine with thymine, or thymine with cytosine). Transversions, on the other hand, involve the replacement of a purine with a pyrimidine or vice versa. For example, substituting an adenine for a thymine is a transversion.

The consequences of a substitution mutation depend on where it occurs within the genome and the resulting change in the amino acid sequence of a protein, if any. If the substitution leads to a codon that still codes for the same amino acid, it is called a silent mutation and typically has no observable effect on the organism. If it results in a different amino acid, it is a missense mutation, which can range in impact from negligible to severe, depending on the importance of that amino acid to protein function. In some cases, a substitution mutation can change a codon that normally codes for an amino acid into a stop codon, leading to a premature termination of protein synthesis. This is known as a nonsense mutation and usually results in a non-functional protein. Substitutions can also occur in non-coding regions of DNA, where their effects can be more variable and less predictable, potentially affecting gene regulation or other regulatory functions.