micro final: mutations and repair mechanisms

point mutations

- most common

- single change of single pair of nucleotide

--> addition/deletion

larger mutations

- less common, more severe

- insertions, deletions, inversions, duplication, and translocations of nucleotide sequences

mutation

change in DNA

spontaneous mutations

arise in cells without exposure to agents capable of inducing mutation

- may result from errors in DNA replication

- may result from action of mobile agent elements (transposon/ jumping genes)

insertions and deletions

additions or losses of nucleotide pairs in a gene

- not much imapct on leaders/trailers

- usually occur in areas of repeated sequences

4 most common mutations

silent. missense, nonsense, and frameshift

silent mutation

change in the nucleotide sequence of DNA that does not alter the amino acid sequence of a protein

missense mutation

a single base substitution that changes codon for one amino acid into codon for another amino acid

nonsense mutation

converts a sense codon to a stop codon

frameshift mutation

results from insertion or deletion of one or two base pairs in the coding region of the gene

mutations in tRNA and rRNA genes

protein synthesis is inhibited

proof reading (DNA repair)

- correction of errors in base pairing made during replication

- errors corrected by DNA polymerase ( I, II, III)

mismatch repair (excision repair)

- correction enzyme scans newly synthesized DNA for mismatched pairs

- mismatched pairs removed and replaced by DNA polymerase and DNA ligase

DNA methylation: used by E.coli

mismatch repair system to distinguish old DNA strands from new DNA strands

- old DNA= methylated

- new DNA= temporarily lack methyl groups

--> mut S= stops error

--> mut H= allows for error to be cut out

nucleotide excision repair

corrects damage that causes distortions in double helix

- 2 types of excision repair systems= nucleotide and base excision repair

- UVA and B scan for dimers

- UVA leaves and recuits UVC to fix the problem