Mutations

Substitutions  the replacement of one base in a DNA sequence by another base i) Silent Mutation has no effect on the operation of the cell  usually occur in the noncoding regions of DNA (introns)  may also result due to the redundant nature of the genetic code ii) Missense Mutation occurs when a change in the base sequence of DNA alters a codon, leading to a different amino acid being placed in the protein sequence  this may alter the folding pattern of the protein and thus the protein may not function properly iii) Nonsense Mutation occurs when a change in the DNA sequence causes a stop codon to replace a codon specifying an amino acid, only part of the protein is created, often lethal to the cell  missense and nonsense mutations arise from the substitution of one base pair for another, this affects one amino acid in the sequence • Deletion or Addition/Insertion  the elimination or addition/insertion of a base pair or group of base pairs from a DNA sequence i) Frame Shift Mutation changes the entire amino acid sequence following the mutation  frameshift mutations may be the result of deletions or insertions  a deletion occurs when one or more nucleotides are removed from the DNA sequence, this shifts all codons and alters them

Inactivation of gene if translocation is within a coding segment i) Translocation  the transfer of a fragment of DNA from one site in the genome (chromosome) to another location  usually occurs between two nonhomologous chromosomes  segments of chromosomes break off and exchange places  some fragments of DNA, called transposable elements consistently move from one location to another in the genome ii) Inversion the reversal of a segment of DNA within a chromosome  no gain or loss of genetic material but may disrupt transcription

x rays UV light chemicals - ethidium bromide (DNA gels), asbestos errors of DNA replication and DNA polymerase 1 fails proof reading

protein with altered function

defective protein