module 10 Flashcards
- define Mutation
- T or F, Mutations are random and usually deleterious (negative impact)
- Rates are (low/high?) in all genomes, vary among organisms and among
different genes within a species
- heritable/permanent change in sequence of genome (i.e. DNA)
- True
- Low
What causes gene conversion?
When resolution of recombination junctions in meiosis leads to change from original nucleotides?
What happens in Transition mutations?
one purine replaces another, or one pyrimidine replaces another
Mutation where a pyrimidine is replaced by a purine or vice versa?
Transversion mutations
Point mutations in coding regions (3)?
- Silent (synonymous)
- Missense
- Nonsense
Determine the type of point mutation
1. no change in amino acid produced
2. change to stop codon
3. change in amino acid produced
- Silent (synonymous)
- Nonsense
- Missense
what are Frameshift mutations?
insertion or deletion of nucleotide
changes reading frame
what can introduce premature stop codons?
frameshifts
Determine the type of REGULATORY point mutation:
- alter consensus sequence nucleotides of promoters
- alter ends of introns, can result in retaining introns in mRNA
- produce new intron splicing sites
- block addition of poly-A tail
- promoter mutations
- splicing mutations
- cryptic splice sites
- polyadenylation mutations
What happens in a Forward mutation?
converts a wild-type allele to a mutant
allele
Which mutation converts mutant alleles to
wild-type or near wild-type allele?
Reverse mutation or reversion
Alterations in number of DNA repeats
occur via what?
strand slippage
- _______ mutation: occurs in tissues not associated with reproduction
▪ is not passed to sexually produced offspring - germ-line mutation: ____________
▪ can be passed to offspring
- somatic
- occurs in reproductive cells (i.e., sperm
and egg)
Tautomeric shifts are a problem during DNA replication because what?
minor tautomeric forms base pair with
incorrect nucleotide
What happens during Depurination?
(leaves apurinic site)
loss of a purine base by breaking the covalent bond linking the nucleotide base to the sugar
After depurination, DNA polymerase will usually compensate by doing what?
putting an adenine opposite the apurinic
site during replication
Chemical mutagens can be classified by their modes of action on DNA as? (3)
- Deaminating agents
- Nucleotide base analogs
- Intercalating agents
what removes amine groups from nitrogenous bases in DNA?
Deaminating agents
What removes amine groups from Adenine and Cytosine, causing mispairing?
nitrous acid (HNO2)
What is 5-bromodeoxyuridine?
acts as an analog of thymine (but can pair
with guanine instead of adenine)
Molecules that fit between DNA
base pairs and distort the duplex?
DNA Intercalating Agents
What is Ethidium bromide used for?
to stain DNA in gel electrophoresis
(is an intercalating agent)
What are Photoproducts?
What causes them?
aberrant structures with additional bonds involving nucleotide
caused by UV irradiation
_________ _______ have additional covalent bonds between adjacent pyrimidines
Pyrimidine dimers
In base excision repair what does DNA glycosylases cut out? What does this leave?
T/F The pathway is active throughout cell cycle
incorrect or damaged bases
apurinic site
Mismatch repair is what type of repair mechanism?
post-replication
Repair enzymes distinguish between the
original, correct nucleotide and the new,
mismatched nucleotide using what?
Methylation on the original strand
In E. Coli, the unmethylated strand is cut where?
GATC methylation site
Nucleotide Excision Repair recognizes and removes what 2 things caused by UV light
damage, that do what to DNA?
Bulky chemical adducts
covalent modifications
distorts DNA
How can pyrimidine dimers be directly repaired?
photoreactive repair
What does photolyase use for energy to break bonds?
energy from visible light to break the bonds
between pyrimidine dimers
The _______ repair mechanism is a ________
mechanism, distinguishing between parent and
daughter DNA strands by __________ of the parent
strand.
a) mismatch; post-replication; methylation
b) base excision; pre-replication; acetylation
c) photoreactive; post-replication; double-strand breaks
d) mismatch; pre-replication; methylation
e) nucleotide excision; post-replication; acetylation
Two repair mechanisms for double-strand break
Nonhomologous end joining (NHEJ)
Synthesis-dependent strand annealing (SDSA
Double-strand breaks can be repaired by an error-free process called what and is this before or after replication?
Synthesis-Dependent Strand Annealing, AFTER
ORDER THESE STEPS OF Synthesis-Dependent Strand Annealing
Sister chromatids re-form, resulting in
replacement of the excised DNA with duplex
identical to the sister chromatid
Trims (excision) one broken strand, Rad51
attaches to resulting 3ʹ overhangs
Replication fork at D-loop synthesizes new
DNA from the intact template strands
Intact sister chromatid has strand invasion
by end of broken strand, forms a
displacement (D) loop
- Trims (excision) one broken strand, Rad51
attaches to resulting 3ʹ overhangs - Intact sister chromatid has strand invasion
by end of broken strand, forms a
displacement (D) loop - Replication fork at D-loop synthesizes new
DNA from the intact template strands - Sister chromatids re-form, resulting in
replacement of the excised DNA with duplex
identical to the sister chromatid
What does the p53 repair pathway control?
How (2 things)?
cell responses to mutation
- Pause the cell cycle
- Direct the cell to undergo
programmed cell death
In synthesis-dependent strand annealing, why does the repair
mechanism result in ‘perfect’ repairs?
a) use of a homologous chromosome as template guarantees
DNA repair without any sequence changes
b) any damaged nucleotides are removed without replacement
c) use of a sister chromatid as template guarantees DNA
repair without any sequence changes
d) any long section with damaged DNA is entirely removed
without replacement
e) SDSA typically does not result in perfect repairs, instead it
usually introduces mutations
What initiates homologous recombination?
DNA double strand breaks
The exchange of genetic material
between homologous DNA molecules
Homologous recombination
In eukaryotes when does homologous recombination occur?
Prohphase I of meiosis
In holiday junction resolution, when must connection between homologs be resolved?
before metaphase I
two ‘north-south’ (NS) resolution or two ‘east
west’ (EW) resolution cuts are defined as
Same sense resolution
____________ sense resolution is much more common: a resolution in which
one Holliday junction is resolved by a NS cut and the other by an EW cut
Opposite sense resolution
A simple test with Salmonella typhimurium tests what?
two mutant forms of S. typhimurium are
used, that cannot synthesize _________, due
to ?
the mutagenicity of compounds
histidine
single base substitution
single base frameshift
Which of the following is true of the Ames test?
(select all that apply)
a) used to scan for forward mutations
b) reverse mutations indicate a compound is
mutagenic
c) can detect substitution mutations
d) can detect frameshift mutations
e) uses mutant strains of E. col
