Module 6 1-8 Flashcards
Mutations are
heritable changes in base sequences that modify the information content of DNA
Forward mutation
changes wild-type to (a different) mutant allele
Reverse mutation
causes mutant allele to revert back to wild-type(reversion)
(reversion)
mutant allele to revert back to wild-type
mutations Can be used as a tool of
genetic analysis
substitution
base is replaced by
one of the other three bases
deletion
block of one or more
DNA pairs is lost
insertion
block of one or more
DNA pairs is adde
types of mutations
point mutations(base substitution) and frameshift mutations
types of point mutation
silence, missense, nonsense
types of framshift mutation
deletion or insertion
What is this an example of
THE CAT ATE THE RAT
HEC ATA TET HER AT
framshift mutation
example of
I HAVE A CAT
I HAVE A RAT
missense mutation
Mutations affecting phenotype occur
very rarely
Different genes mutate at
different rates
Different species have
different mutation rates
The mitochondrial genome has a ________ mutation rate than the
nuclear genome
different
Rate of forward mutation is almost always _____ than rate of reverse
mutation
higher
Mutation rate in human sperm is _____ than in human eggs.
higher
Resistance arises from mutations that exist ______ exposure
to bacteriocide
before
After exposure to bacteriocide, the bacteriocide becomes a _______
selective agent
selective agents kill ___ allowing _____ cells to live
the nonresistant cells; preexisting
mutations occur _____ at any time
randomly
Mutations ______ in particular genes as a direct response to environmental change
do not arise
Luria and Delbruck Experiment tried to answer the question (2)
Do mutations occur spontaneously or are they a reaction to a selection pressure?
did they mutate before infection to after infection to allow survival
before the Luria and Delbruck experiment it was known that some bacteria can
survive infection with bacteriophages
first pediction of luria and delbruck experiment
parallel cultures of bacteria should all show roughly same number
of resistant colonies (induced by infection)
second prediction of luria and delbruck experiment
if mutations are random and occur before treatment, parallel
cultures should display varying amounts of resistant colonies
ledeberg experiment design-
bacteria was infected with bacteriaphage and cultures plated onto petri dishes resulted in varied numbers of resistence to bacteriaphage. reistence was random supports hypothesis 2
ledeberg experiment also tested to see
if mutations were spontanious or induced
what was the experiment premise for ledeberg experiment
replica plating
ledeberg experiment: what happened
petri dish with number 1 senstive and resistence bacteria to antibiotics when velvet palced over stamper bacteria can be picked up on velvet which is then placed in petri dish with penecilin. only reistsnt colony forms.
result of ledeberg experiment
resistent were all in the same area. which means mutation occurs. and not a result of penecillin.
what Causes-Chemical and Physical Assaults (2 ways)
wild type-> natural process of mutagen-> dna damage->dna replication-> mutation
wild type-> natural process of replication in prescense of mutagen-> dna base sequence error->dna replication-> mutation
mutations can be avoided by
DNA repair
mutations can be ____ or caused by _____
spontaneous; mutagens
what 2 different processes can mutagens do to cause changes in DNA
depurination, deamination
depurination
Process: This occurs when a purine base (adenine or guanine) is lost from the DNA molecule, creating an apurinic site (AP site).
depurination effect
When DNA is replicated, the absence of the base can lead to the incorporation of an incorrect base (often adenine), potentially resulting in a mutation.
deamination
Deamination involves the removal of an amino group from a nucleotide base. For instance, cytosine can be converted to uracil, and adenine can be converted to hypoxanthine.
deamination effect
This can lead to base pairing changes during DNA replication. For example, uracil pairs with adenine instead of guanine, which can result in a transition mutation (changing a pyrimidine to another pyrimidine or a purine to another purine
can radiation cause mutations?
yes
radiation can cause
mass deletions
radiation with light can cause
thymin dimers/pyrimidine dimers
thymine dimers/pyrimidine dimers can cause problems with
dna rpelication
mutations can be caused by oxidation from ________
free radicals
oxidation from free radicals can cause
incorrect nucleitide inserted making mutant sequence
mutations can also be caused by
Unequal crossing over can cause insertions and deletions
Transposable elements can jump into genes.
what enzyme proofreads
polymerase
when wrong base is added proofreading enzyme will
excise wrong base, and add correct one
base tautomers can cause mutations by
base tautamer is placed in location and alters base pairing abilities
trionucleotide expansions seen with
fragile x and hutchinsons disease
Trinucleotide Expansions Can Destroy
Gene Function
Trinucleotide Expansions mechanism?
unknown maybe a “stutter” during replication
Trinucleotide can either have ______ or _____
repeat expansion or repeat contraction
Mutations Can be Fixed
by
enymes
base excision repair
altered base removed->endonuclease cuts at apurinic site->exonuclease remove nucleotides near cut->polymerase fills cut->ligase seals cut
Nucleotide Excision
repair
Enzymes release
damaged regions of
DNA. Repair is then
completed by DNA
polymerase and DNA
ligase
types of mutation repairs
Nucleotide Excision
repair
base excision repair
severe mutagens can break
both strands
when severe mutagens break both strands how do enzymes fix this
enzymes come in, trim edges, then join together with ligase
this process uses additional proteins
double stranded break fixes are normally very
error prone
Methyl-directed mismatch
repair in bacteria
Fixes uncorrected mistakes of
DNA polymerase
methal tags are on
parental strand
______ Mutagens can be used to increase mutation rates
mutagens
H. J. Muller – first discovered that
x rays increase mutation rates in drosphilia
the more x rays the more
mutations
scientists can use chemical mutagens to replace a
base
chemicals that can alter base by
hydroxylating agents, alkalyzing agents, or deaminating agents
some chemical mutagens act as
Intercalating agents
Intercalating agents inserts itself between
base pairs
when Intercalating agents inserts itself between base pairs
effects dna replication, leads to insertions and deletions
Intercalating ___________ allows us to see DNA using UV light
ethidium bromide
Germ line mutations
passed on to next generation and
affect the evolution of species
Somatic mutations
affect the survival of an individual
cell cycle mutations fall under
somatic mutations
cell cycle mutations can cause
cancer
Because of potential harmful effects of mutagens to individuals, tests have been developed to identify _____
carcinogens
carcinogens
cancer causing
ames test was developed by
bruce ames in 1974
ames test is used to identify possible
carcinogens
what are the 2 major consequences of mutations
germ line mutation
somatic mutation
bruce ames used salmonella since it had
a mutation already
ames test-
contorl experiment- histodine, and rat liver enzyme mixed and plaed onto medium with no histodine. few bacteria colonies
experiment- histodine, rate liver enzyme, and thing being tested for mutagen. mixture is placed onto medium with no histodine. many bacteria colonies form
bacteria used in ames is
his- mutant bacteria
his- bacteria cant make histodine and cant make histodine unless
back mutation which allowd bacteria to produce histodine.
Salmonella strain has a mutation in a gene necessary to make the amino acid
histodine
The strain is histidine auxotroph
– it is unable to grow without
added histidine
Revertants
will grow on minimal medium plates without
histidine
what do revertents due for salmonella strain taht cant grow histodine
will make new mutations that re-establish ability to make histidine
the salmonella strain also has a mutation that
inactivate NER (nucleotide encision repair) , and a mutation that makes cell wall more permeable for chemicals
Complementation testing tells us whether
wo mutations are in the same or
different genes
no complementation means mutations are
in the same gane
complementation means mutations are in
differeent genes
If a gene is linear then
mutations should be able to occur
independently in the same gene in different locations
f a gene is linear, recombination within a gene should restore
wild type
