Lecture 3/17 Flashcards
If the bar eye is X-linked, is a male more likely to inherit it if it’s a recessive or dominant gene?
it doesn’t matter, as it will only get one copy. if the copy it gets is the bar, it will have bar eyes
are mutagens only seen in the environment?
no, they are all actually endogenous (naturally occurring in the body) as well as environmental
which is worse – increased ROSs or DSBs?
double stranded breaks are worse
what causes a DSB?
X-rays, UV boxes, radiation treatment
what is an intercalating agent? how is it a mutagen?
something that inserts itself between bases, causing a disruption in DNA replication/repair/recombination –> it makes the DNA think there is a mismatch, which leads to the deletion of a base pair or insertion of a random base pair
what are the different types of mutagens?
intercalating agents, base analogs
what are base analogs? what’s an example and how does it work
molecules that mimic the structure of a standard base. example is uracil with bromide. uracil with bromide-rare state behaves like cytosine, so it pairs to guanine
what are the effects of a somatic mutation?
- non germ cells
- not transmitted to next generation
- can affect survival of an individual
- can lead to cancer, but doesn’t affect progeny
what are the effects of germ line mutations?
- occur in gametes/gamete precursor cells
- doesn’t affect the parent with the mutation, only future generation
- transmitted to next generation
- provides raw material for natural selection
- these mutations are often cancerous
what can cause a mutation to not be permanent?
if the DNA repair occurs before replication
what is the effect of a mutation dependent upon?
if the mutation is corrected and if it’s in a somatic cell or germline
what helps DNA be repaired before replication
having a vigilant repair system
at what point are mutations usually corrected? does it do a good job? how does it work?
during proofreading, it’s highly accurate. mispaired base is recognized and excised by 3’ to 5’ exonuclease activity of DNA pol; improves fidelity of replication 100-fold
what is alkyltransferase?
it removes alkyl groups (alkyl transferases are naturally occurring)
how do prokaryotes respond to UV ray-caused thymine dimers?
photolyase is used to split the covalent bond of thymine dimers in presence of light
which kinds of repair are single strand base repair?
homology-dependent repair:
- base excision repair
- nucleotide excision repair
which kinds of repair are for double stranded breaks?
correction of DNA replication errors:
- methyl-directed mismatch repair
how does base excision repair work? (5steps)
- deaminated C DNA looks like a U, glycosylase recognizes and cleaves the C from the sugar, leaving an AP site.
- AP endonuclease cuts in and nicks the backbone at the AP site around where the mutation occurred
- DNA exonucleases remove nucleotides near the nick because there’s a free 3’ and 5’ end (which is bad)
- DNA pol I/beta synthesizes new DNA to fill the gap
- DNA ligase seals the nick
what is an AP site?
an apurinic or apyrimidic site
does AP endonuclease make a ss or ds cut?
single stranded
what do glycosylases do?
recognize different types of DNA damage and cleave them
what happens if you have mutations in/are missing glycosylases?
you die, these are essential enzymes
what type of repair uses glycosylases?
base excision repair (ber)
what happens in response to UV exposure?
thymine dimers
