mibo ch 16 pt 2

mutations

mutation

heritable change in DNA sequence
changes can be small (affecting 1 nucleotide) or larger (affecting many nucleotides)
both can have dramatic effects

mutations arise in

diverse ways

spontaneous mutations

rare because of the efficiency of RNA proofreading and repair pathways

reasons mutations can arise

1. tautomeric shifts in DNA bases that alter base-pairing properties

2. oxidative deamination of bases

3. formation of apurinic sites

tautomeric shifts in DNA bases that alter base-pairing properties

A-T pair changes to A-C pair

oxidative deamination of bases

C changes to U on DNA strand which then pairs with A

formation of apurinic sites

loss of base from sugar backbone
harder to repair
insert something random → mutation moves through progeny

frameshift mutation

insertion or deletion of nucleotides that cause the reading frame to change
dramatically changes the protein sequence after the site of the mutation, often causing them to lose their function

nonsense mutation

converts a codon that normally encodes from an amino acid to a stop codon
causes the formation of truncated proteins, often causing them to lose their function

missense mutation

converts a codon that encodes from one amino acid to a codon that encodes for a different amino acid
sometimes impacts the protein function, depending on whether the substitution is conservative or nonconservative and where the amino acid is located within the protein structure (active site)

silent mutation

the amino acid that the codon encodes for is unchanged
rarely impacts the protein function

frameshift mutations occur at

short stretches of repeated nucleotides
pairing of template and new strand can be displaced

insertion/deletion of DNA sequence changes

the open reading frame of the gene termed a frameshift

which process is the point mutation occurring in if it is a heritable change?

replication

what enzyme is creating the mutation?

DNA polymerase

What step is a mutation most likely to impact?

see effect in protein activity
translation (new aa or altering reading frame)