University:
Western Sydney University
Course:
MEDI 2003 | Clinical Sciences 2
Academic year:

2024
Views:

357

Pages:

2
Author:

Mariam A. A.

Point Mutation Definition: A change in one nucleotide in DNA, such as substitution of one nucleotide for another, an insertion or deletion of a nucleotide. Silent A silent mutation is a change in the sequence of nucleotide bases which creates DNA, without a subsequent change in the amino acid or the function of the overall protein. Nonsense A nonsense mutation is a genetic mutation in a DNA sequence that results in a shorter, unfinished protein product. Missense A genetic alteration in which a single base pair substitution alters the genetic code in a way that produces an amino acid that is different from the usual amino acid at that position. Categories of point mutations: • • Coding Point Mutation: occurs within the coding region of DNA that specifies for a protein whereas the latter occurs outside the coding region of DNA. Non-Coding Point Mutation: non-coding point mutation does not affect the amino acid sequence of polypeptide chains in protein synthesis whereas coding point mutation does. Causes: • • • Point mutation can arise due to spontaneously (natural) or be induced (unnatural). Spontaneous mutation deals with errors in normal DNA replication that are not repaired by enzymes resulting in insertion or deletion of a nitrogenous base from DNA sequence. Induced mutation can be due to the exposure to environment agents such as ionising radiation, chemicals or naturally occurring substances. Processes: Point mutations involve a substitution, deletion, or insertion of one nucleotide base. Deletions and insertions result in a frameshift mutation of triplets, so polypeptide chains are significantly distributed or terminated. Effects: • • • • Point mutations cause new alleles in germ-line and somatic cells If a substitution of a nitrogenous base occurs in a ‘non-coding’ part of the DNA it could result in the substitution of one amino acid for another in polypeptide synthesis - Substitution in part of the “non-coding” DNA could alter the expression of a gene. Some point mutations may have no observable impact on the phenotype Insertion of an extra nucleotide or deletions of a nucleotide. These may result in frame shift mutations. - Frame shift mutations: A frameshift mutation is a type of mutation involving the insertion or deletion of a nucleotide in which the number of deleted base pairs is not divisible by three