LECTURE 12 Flashcards
what are the important regions of a bacterial gene?
promoter
antileader (on template strand)
coding region
antitrailer
terminator
in what way is RNA made, and what strand is it identical to?
made in 5’-3’ direction, identical to non template strand
what are the different types of mutations in DNA (5)?
base substitution
deletion
inversion
transposition
duplication
what can mutations lead to?
morphological
- colonial or cellular
lethal mutations (essential) genes
biochemical mutations (pathways)
resistant mutant (antibiotic, chemicals)
how can the cell type change if there is a biochemical mutation?
cell can go from a prototroph to an auxotroph or vice versa
prototroph: can make their own stuff
auxotroph: need to import it from the outside
why can mutations happen?
- spontaneous, happen in DNA replication
- can be induced by mutagens
physical (UV, X ray, gamma ray)
chemical (5-bromouracil)
what are the different types of point mutations?
only one base pair changes
- silent (does not change the codon)
- missense (changes the codon)
- nonsense (creates a stop codon)
- frameshift (deletions and insertions)
what is a forward and reversion mutation?
forward mutation= starting from the reference wild type
reversion mutation= back to wild type phenotype, but that doesn’t necessarily mean that the sequence is the same
- original wild type sequence
- new codon but same AA (silent)
- new codon but similar AA (missense)
where can a suppressor mutation be?
- intragenic: same gene but another location
- extragenic: different location
what are some mistakes that can be made by DNA polymerase 3 and what does that lead to?
- slippage in the new strand
leads to an addition in the next round of replication - slippage in the parental strand
leads to a deletion in the next round of replication
how is the thymine dimer created and what is it?
through exposure to UV, a covalent bond between thymines is created, and that creates a shape distortion of the DNA
what is 5-bromouracil and how can it be incorporated into the DNA?
exists in two forms: keto and enol
the two forms are present in a 50:50 ratio
the keto form can bind to adenine
the enol form can bind to guanine
this means that 5-bromouracil can be incorporated into the sequence by DNA pol III
-> you can induce mutations with this
what are mechanisms of DNA repair and what do they deal with?
- proofreading activity of DNA polymerases (3’ to 5’ exonuclease activity) (can still make mistakes)
- mismatch repair
not complementary base pairs - nucleotide excision repair
distorted DNA (thymine dimer) - base excision repair (backbone intact but base is missing)
apurinic and apyrimidinic sites
damaged or unnatural bases (RNA in DNA)
how does mismatch repair work?
- the MuS protein finds a mismatch
the MutS/MutL complex is bound to MutH, which is already bound to a hemimethylated sequence - MutH makes a cut in the nonmethylated strand
- exonuclease begins at this cleavage site and digest the nonmethylated strand beyond the base mismatch
- DNA polymerase fills in the vacant region
- DNA ligase seals the end and the mismatch has been repaired
how does nucleotide excision repair work?
- the UvrAB complex tracks along the DNA in search of damaged DNA
- after damage is detected, UvrAB is released and UvrC binds
- UvrC makes cuts on both sides of the thymine dimer
- UvrD is a helicase that remove the damaged region
- UvrB and UvrC are also released
- DNA polymerase fills the gap and DNA ligase seals the gap
