Mutations lectures (2) Flashcards
why are bacteria good model systems?
- unicellular (change in phenotype WILL affect that cell)
- single chromosome - haploid - no competing alleles
- replicate by binary fission
- > all daughter cells identical to parent
- > no genetic variation
- simple gene structure
Stop codons
UAA, UAG, UGA
mutants in bacteria
auxotrophs
amino acid/vitamin
mutations in bacteria
resistance
antibiotics/phage/toxic chemicals
mutations in bacteria
inability to use a substrate
sugar
non-selective media
all cells grow so test individual colonies
selective media
e.g. antibiotic present / absence of amino acid
indicator media
e. g. MacConkey Agar
- identifies whether bacteria use lactose
silent mutation
different codon, same amino acid
missense mutation
different amino acid, different protein
nonsense mutation
changes to stop codon, cuts protein short
frame-shift mutation
adds/removes nucleotide, shifts sequence
deletions
removes genes, may change phenotype
insertions
adds gene(s), may change phenotype
rearrangements
reorders gene (s), may not change phenotype
point mutations
affect one single gene
types of point mutations
- silent mutations
- missense mutations
- nonsense mutations
- frame-shift mutations
types of larger-scale mutations
- deletions
- insertions
- rearrangements
reverse and suppressor mutation types
- forward mutation
- reversion
what is a forward mutation?
wild type sequence -> mutant sequence
what is a reversion mutation?
1) reverse
mutant sequence -> wild type sequence
2) suppressor
mutant sequence
Types of reversion mutation
- reverse
- suppressor
Mutation Rate formula
= ratio in a population of (number of mutants/number of wild types)
requirements for measuring frequency of mutation
large populations
special techniques
Induced mutations are caused by…
mutagens and radiation
transition mutations
pyrimidine -> pyrimidine
purine -> purine
transversion mutations
pyrimidine -> purine
purine -> pyrimidine
why are transition mutations more common than transversion mutations?
pyrimidines and purines (two rings) are more structurally different from each other than within their group.
Spontaneous mutations
independent of selective (dis) advantage to host
each gene mutates at a characteristic rate
each type of mutation occurs at a characteristic rate
Base Analogues
molecule similar to one of the four DNA bases
Base analogues incorporated into DNA…
ONLY at replication
Base analogues can…
pair with a normal base
Example of a base analogue to thymine
5 - bromouracil
nitrous acids causes what type of mutations?
transitions A-T -> G-C
alkylating agents cause what type of mutations?
transition A-T -> G-C
Intercollating chemicals
planar, ringed molecules the size of a base pair (bp)
examples of intercollating chemicals
acridine
ethidium bromide
order these mutations in their ease to be fixed and tolerance to mutation by radiation
- ssDNA breaks
- nucleotide substitution
- dsDNA breaks
- nucleotide substitution
- ssDNA breaks
- dsDNA breaks
DNA repair mechanisms
Apurine gap repair Mismatch pair Photoreactivation repair Excision repair Post-replication repair
Apurine gap repair
uses AP endonuclease
- removed damaged base
- ss gap filled by polymerase
if no repair inserts A
Mismatch pair
nearby ss cut and excision of ssDNA past mismatch
DNA polymerase repairs gap
Photoreactivation repair
light driven process
various enzymes with specific properties
Excision repair
multi-enzyme system
enzymes identify & instant removal
polymerase repairs
Post-replication repair
polymerase can't replicate across damaged DNA, leaves gap gap filled by strand exchanged from another dsDNA secondary gap (from where strip take - not damaged) repaired by polymerase
