Base-pair substitution

Base-pair substitution is a type of mutation that involves the replacement of one nucleotide base pair with another in the DNA sequence. This can lead to significant changes in the protein produced by the affected gene, potentially resulting in a variety of genetic disorders or diseases.

Overview

A base-pair substitution occurs when one nucleotide base pair in the DNA sequence is replaced by another. This can happen during DNA replication, when the DNA polymerase enzyme makes a mistake and incorporates the wrong nucleotide into the newly synthesized DNA strand.

There are two main types of base-pair substitutions: transitions and transversions. Transitions involve the substitution of a purine for a purine (adenine (A) with guanine (G), or vice versa) or a pyrimidine for a pyrimidine (cytosine (C) with thymine (T), or vice versa). Transversions, on the other hand, involve the substitution of a purine for a pyrimidine, or vice versa.

Effects

The effects of a base-pair substitution can vary widely, depending on the specific change and its location within the gene. In some cases, the substitution may have no effect on the protein produced by the gene, a phenomenon known as silent mutation. This is because the genetic code is degenerate, meaning that multiple different codons can code for the same amino acid.

In other cases, the base-pair substitution can result in a missense mutation, where the changed codon codes for a different amino acid. This can alter the structure and function of the protein, potentially leading to a genetic disorder or disease.

A particularly severe type of base-pair substitution is a nonsense mutation, where the changed codon becomes a stop codon. This causes the protein synthesis to terminate prematurely, often resulting in a nonfunctional protein.

See also

• Point mutation
• Frameshift mutation
• Mutation rate
• Genetic variation