Mutations Section 12-4 Pages 307-308

Genetic Mutations A mutation is a change in the nucleotide sequence of DNA. Mutations that produce changes in a singe gene are called gene mutations. Mutations that produce changes in whole chromosomes are chromosomal mutations.

Gene Mutations Gene mutations deal with the change of a single nucleotide in the chain. The effects can be: no change in the protein serious defects in protein structure Which can include: shortened proteins, due to a premature stop codon proteins with extra amino acids due to a lack of a stop codon proteins with incorrect amino acids due to a substitution

There are 3 main types of gene mutations: Substitution Deletion Insertion

Substitution Substitution occurs when a single nucleotide is switched with a different base pair. RESULTS: - ONE incorrect amino acid in the manufactured protein most times. -OR- - Sometimes with a substitution there will be no change in the protein. Substitutions are often called point mutations because they only affect 1 point in the sequence.

Deletion Deletion occurs when a single nucleotide is dropped from the sequence. When this happens, the remaining nucleotides move up one spot in the sequence. RESULTS: -A shortened protein because a premature stop codon formed -OR- - A lengthened protein because of a late stop codon. - No protein being made at all. ANALOGY: A person leaves the line for movie tickets and everyone behind them moves up a spot closer to the counter.

Insertion Insertion occurs when a single nucleotide is added to the sequence. When this happens, the remaining nucleotides move back one spot in the sequence. RESULTS: - A shortened protein (a premature stop codon formed) -OR- - A lengthened protein (a late stop codon) - No protein being made at all. ANALOGY: A person cutting the line for movie tickets and everyone behind them moves a spot farther from the counter

Frameshift mutations Deletions and insertions are called frameshift mutations because they shift the “reading frame” of the genetic message. Frameshift mutations can change every amino acid that along the point of the mutation Frameshift mutations can alter a protein so much that it is unable to perform its normal functions.