Lecture 22 Flashcards
do most mutations occur in somatic cells or gamete cells?
somatic cells
when are mutations inherited?
if mutations are in gametes
what percent of offspring carry the mutation if a gamete is mutated?
50%
why do only 50% of F1 generation carry mutation from germ-line mutant?
mutation occurs randomly so only 1 homologous chromosome will get mutation, so only F1s that inherit that chromosome will have mutation
chromosome mutation VS insertional mutation VS point mutation
chromosome mutation: gain/loss of all or part of a chromosome
insertional mutation: insertion of large region of DNA
point mutation: changes in 1 nt
2 categories of point mutations
- base substitution
- indel
2 types of base subtitutions
- TRANSITION
- TRANSVERSION
what is a transition base substitution?
purine –> purine
pyrimidine –> pyrimidine
what is a transversion base substitution?
pyrimidine –> purine
purine –> pyrimidine
which bases are purine?
A and G
which bases are pyrimidine?
C and T
4 types of point mutations in ORF
- Synonymous/Silent Mutation
- Nonsynonymous/Missense Mutation
- Nonsense Mutation
- Frameshift Mutation
what happens in a Synonymous/Silent Mutation?
nt sequence changes but aa sequence does not change
what happens in a Nonsynonymous/Missense Mutation?
nt sequence changes and changes aa sequence
2 types of Nonsynonymous/Missense Mutations and what they mean
- conservative –> mutant encodes chemically similar aa
- non-conservative –> mutant encodes chemically different
what happens in a Nonsense Mutation?
change sequence of codon that codes for an aa into a stop codon
what does the effect of a Nonsense Mutation rely on?
depends on the distance from 3’ end of ORF
what does a Nonsense Mutation lead to?
triggers nonsense-mediated decay which degrades mRNA
what causes a Frameshift Mutation? and what does it lead to?
caused by an insertion or deletion, leading to a change in the translation reading frame for codons downstream of the mutation
3 effects of point mutations on gene function
- WT function
- LOF
- GOF
2 types of LOF and what they mean
- HYDROMORPHIC: weak/partial function
- NULL: non-functional or not produced
3 types of GOF and what they mean
- HYPERMORPHIC: protein is hyperactive
- ECTOPIC: more protein made or made in wrong time/place
- NEOMORPHIC: protein gains new function
where in the genome can point mutations be found?
in coding AND non-coding regions
example of gene that has LOF after mutation
p53
example of gene that has GOF after mutation
RAS
what happens to RAS function with GOF?
becomes constitutively active
what is the mutation that occurs to make RAS constitutively active?
G –> T
Gly –> Val
how does mutation cause RAS to become constitutively active?
blocks conversion from GTP to GDP so RAS is stuck in active form and cells receive growth signal
mutations in non-coding regions affect: (5)
- transcription
- splicing
- stability
- translation
- function
2 ways point mutations can affect mRNA splicing
- make new splice site in wrong place
- remove splice site so there is no splicing
outcome of PBRM1 mutation on cancer patients
PBRM1 mutation causes worse cancer prognosis
describe what happens with a BAP1 mutation
GGT –> GGG, still Glycine
exon 11 spliced out and causes framshift that makes a stop codon
mRNA and protein are degraded (LOF)
therefore, mutation is silent in coding region but visible in translation
what do Northern and Western blots look like if there’s a MISSENSE MUTATION?
aa is just swapped, so northern and western blots look the same as WT
what do Northern and Western blots look like if there’s a NONSENSE MUTATION?
makes early stop codon, so northern looks same as WT but western shows smaller protein OR mRNA degradation via NMD
what do Northern and Western blots look like if there’s a FRAMESHIFT MUTATION?
can make smaller protein, so northern looks the same as WT but western shows smaller protein OR mRNA degradation via NMD
what do Northern and Western blots look like if there’s a REGULATORY REGION MUTATION?
northern and western both show no band
2 origins of spontaneous mutations
- errors in DNA replication
- chemical changes to DNA
2 ways that errors in DNA replication can occur
- base mispairing
- strand slippage
what is the DNA pol error rate?
300 mutations per mitosis
are most DNA pol errors harmful?
no, >99% are fixed by DNA repair mechanisms
2 types of chemical changes in DNA that lead to mutation?
- depurination
- deamination
what happens to DNA if there are no proofreading mechanisms?
any mismatch = mutation
3 types of errors in base pairing
- tautomeric base pair
- ionized base pair
- wobble base pair
what is a tautomer?
isomaer of a base with diff positions of atoms and their bonds, the forms are in eqb
what happens when a thymine base pairs with an enol form of guanine?
error in replication causes T-G mismatch
when the DNA is replication, one product will be normal C-G pairing and the mutant product will be A-T pairing
when does a mismatch become permanent?
once replicated
