T4M4- DNA mutations and applied lecture Flashcards
are mutations always bad?
no they can cause either destructive cellular responses, beneficial adaptations or be perfectly harmless
what can mutations be a result of
environmental factors, spontaneous mutations or error in DNA replication
what are the most common types of mutations?
spontaneous
do viruses have low or high mutation rate?
high
why are RNA viruses more prone to mutation
due to delicate nature of backbone
- no proofreading capability
what will happen to a division of cell with mutation?
new cell will have part of mutation
what happens if a mutation occurs in non dividing (post mitotic) cell in G0 phase?
effect of mutation is negligible
are mutations inherited in somatic cells?
no
are mutations inherited in germ cells? why
yes because germ cells produce offspring
what did joshua and esther lederberg’s experiment in 1952 show
mutations are random and not directed
what type of nutrients were in the experimental setup of lederberg
nonselective supplemented nutrients
- so that cell can grow and form bacteria
what was in the new selective plate?
antibiotic penicillin
what is this process of stamping called
replica pleating
- preserves relative arrangements of colonies relative to original plate
what did they find after stamping
only few colonies survived penicillin on plate 2
what did they predict about the new colonies that survived
carry mutation resistant to antibiotic for penicillin
what does the process of replica mean
original colony isolated from original agar and used to test
after testing what did they discover about the mutations?
it existed in population prior to exposure
what can repair breaks in DNA backbone?
DNA ligase
why do most cells contain DNA ligase
for replication and repair of single stranded breaks
define proofreading
scanning DNA for potential mismatches
what does a mismatch cause
kink in DNA molecule
what causes a single stranded cleavage of mismatched DNA in the backbone
nuclease
what happens once nuclease cuts the backbone
another enzyme removes successive nucleotides from DNA strand
what happens if DNA accidently incorporates uracil
DNA-uracil glycosylase will cleave uracil from backbone, leaving deoxyribose sugar with no base
what is the lack of base detected by
AP endonuclease
what does AP endonuclease do
cleaves backbone of lack based area, leaving gap for addition of new nucleotide
what happens in a base excision repair
damaged base is recognized and removed from the DNA backbone by one of the DNA glycosylases
what is nucleotide excision repair similar to
mismatch repair
what does a nucleotide excision repair do
removes and replaces one or more nucleotide bases in a “cut and patch” way
how are bases cleaved during nucleotide excision repair
bases signal to enzymes to cleave DNA backbone on both sides of damaged bases
what are small point mutations
single nucleotide pair changes
where do small point mutations arise and why
during DNA replication due to escaping proofreading mechanisms
what are the most common types of small point mutations
single nucleotide base substitution
what is another name for single nucleotide base substitution
single nucleotide polymorphisms or SNP
what mutation causes sickle cell anemia
a missense mutation that causes a single amino acid substitution in the hemoglobin molecule
what happens as a result of the base change in sickle cell anemia
translation of valine instead of glutamate
define missense mutation
when a single nucleotide base is changed, resulting in a a different amino acid
define silent mutation
occurs when a change in nucleotide pair has codon substitute but still produces same amino acid
- possible due to gene redundancy
what do most substitution mutations lead to
missense mutations
what is a nonsense mutation
a point mutation which gives rise to an amino acid which codes for stop codon
describe result of nonsense mutations
-causes premature translation termination
-has shorter polypeptide sequence
-can lead to nonfunctional proteins
define insertion
when one or more extra nucleotide is inserted into replicating DNA
define deletion
skipping or removing more than one nucleotide during replication
what determines degree of impact of insertion or deletions
size of mutation
what mutation causes cystic fibrosis
deletion of 3 nucleotides in CFTR channel
define a frameshift mutation
occurs when insertion or deletion does not happen in a group of three
what does a frameshift mutation lead to
-improper grouping of nucleotides
-massive missense mutations
-ends in nonsense and nonfunctional proteins
what happens when a centromere is lost
entire chromosome is lost because not allocated into daughter cells
what happens if there is a deletion in one homologous chromosome
organism may persist depending on if other homologue can compensate to provide gene product needed for survival
what can chromosomal duplication cause
little harm due to homologous chromosome
what can duplication lead to
new gene being formed with similar function to original gene
define inversion
when normal sequence is reversed
what causes an inversion?
a segment breaks off and reattaches in reverse order
is inversion serious?
no because all genes are present
what does inversion explain?
long term chromosomal evolution
define reciprocal translocation
portion of one chromosome attach to non homologous chromosome and exchange terminal chromosomal fragments
when does reciprocal translocation occur
happens when there is a break and translocation carried out before the break required
where does reciprocal translocation occur
in non coding regions of DNA in large genome
explain duplication and divergence effect with globin proteins in fetuses
two gamma globin genes are almost identical in amino acid sequence but expressed at different points
explain duplication and divergence effect with globin proteins in adults
adult delta and beta hemoglobin differ in amino acid sequence and are expressed at different levels
what are miRNAs
microRNAs- short non coding RNA that regulate gene expression post transcriptionally
what are TUFs
transcripts of unknown function- their role in the cell is unknown
what does the alternative splicing hypothesis state
eukaryotes do not require large numbers of distinct genes
how similar are chimp and human genes?
98.8%
where are the differences in genome found between chimps and humans
in the regulatory sequences
- responsible for phenotypic differences
