DNA and mutations SC.912.L.16.4

Mutations Alterations in DNA sequence Some are part of normal DNA variation Caused by chemical and physiological agents and errors in DNA replication Cells can repair some mistakes If not repaired, changes in DNA sequence are made permanent by DNA replication

Point mutations: Single base mutations: 1. Missense mutation: leads to an amino acid change 2. Silent mutation: does not change the amino acid (NO PHENOTYPIC CHANGE!) 3. Nonsense mutation: causes premature stop-codon

Frameshift mutations: insertion/deletion duplication translocation Altered reading frame Severe impacts on protein structure-will see a phentotypic change, or potentially lethal

Effects of mutations Insignificant (no phenotypic change) 1) Some nucleotide substitution mutations 2) Degeneracy of codons a) More than one codon for most amino acids b) Third nucleotide position is often not important e.g., G-U-n = valine; U-C-n = serine; C-G-n = arginine 3) Functional equivalency of amino acids As long as the amino acid can still function as it is supposed to, there will most often be no phenotypic change

Effects of mutations Harmful 1) Some nucleotide substitutions 2) Nucleotide insertions or deletions result in frameshifts, null mutations 3) Altered or lost protein function If the amino acid and/or protein loses function, there will be a phenotypic change, or mutation will be lethal