Mutations Flashcards
What is another name for single base substitutions?
single nucleotide polymorphins (SNPs)
C -> T changes occur as what proportion of SNPs?
2/3
Which are more common: transitions or transversions?
Transitions
What is a transition?
A base substitution of purine to purine or pyrimidine to pyrimidine.
What is a transversion?
The base substitution is purine to pyrimidine or vice versa.
What is a missense mutation?
One amino acid is substituted by another.
What is a silent mutation?
The substitution does not affect the amino acid coded for.
What is a nonsense mutation?
The amino acid codon is mutated to a stop codon.
What is a frameshift mutation?
The reading frame of the mRNA is altered.
What are conservative missense mutations?
Amino acid substitutions that are better tolerated because the amino acids are similar.
When premature termination occur, what process degrades the protein?
Nonsense mediated decay (NMD)
What things can cause base changes?
tautomeric shift DNA strand slippage chemical alteration of DNA bases chemical disruption to DNA base stacking UV light radioactive substances
What is tautomeric shift?
A proton briefly changes position in one of the bases that causes altered base pairing properties.
C-A
G-T
What are the 2 ways that slippage can occur?
new synthesised strand loops out resulting in addition of one nucleotide to new strand
template strand loops out resulting in omission of one nucleotide from the new strand
What does nitrous acid do?
Replaces amino groups with keto groups
What does ethylmethane sulphonate (EMS) cause in DNA?
removal of purine rings, apurinic sites can be paired with any base
Name a base stacking mutagen and where it is found
IQ
found in cooked meats and cigarette smoke
What does IQ do?
intercalates between DNA strands forcing the bases further apart, causes misreading by DNA polymerase
What other molecule (other than IQ) intercalates with DNA?
Ethidium bromide
What is thymine dimer formation?
UV light photons cause adjacent thymine bases to base pair with one another.
What is nucleotide excision repair?
enzymes detect mismatched bases by scanning along DNA
replaced with correct base pairs
“patch’’ of DNA sequence is replaced
Used to correct damage done by UV photons
What are the 3 types of single strand DNA repair?
mismatch repair
Nucleotide excision repair
Base excision repair
What is excision repair?
Removal of incorrect base pairs
Which genes encode mismatch repair enzymes?
MLH1
MSH2
MSH6
What are the 6 new characteristics of tumour cells?
divide independently of external growth signals
ignore external anti-growth signals
avoid apoptosis
divide indefinitely without senescence
stimulated sustained angiogenesis (new blood vessels form)
invade tissues and establish secondary tumours
What do all cancer cells exhibit?
chromosomal instability and microsatellite instability
Which genes are known to be linked to familial breast cancer?
BRCA1
BRCA2
What are the proteins from the genes BRCA1 and BRCA2 usually for?
involved in detecting DNA damage and signalling to cell cycle checkpoints
What are proto-oncogenes?
genes that perform a range of cell cycle functions
can be activated by retroviruses to oncogenes by key amino acid substitutions
What does the 2 hit theory refer to?
cancer genes tend to harbour recessive mutations but dominant patterns of inheritance
What is the most common CF mutation?
p.F508del
phenylalanine is deleted
What is the most common form of mutation?
single base substitutions
How do we perform SSCP mutation scanning?
- looking at individual DNA strands
identify mutated region of gene
PCR
amplified DNA is heated then cooled rapidly
individual strands base pair with themselves
use DNA electrophoresis and stain
What does SSCP stand for?
Single Strand Conformation Polymorphism
What are the 3 ways of obtaining foetal DNA?
amniotic fluid sample
chorionic villus sample
foetal DNA in maternal blood
When can we perform amniocentesis and what is the risk of miscarriage?
15-20 weeks of gestation
0.5-1.0% chance of miscarriage
When can we perform a chorionic villus biopsy and what is the risk of miscarriage?
10-13 weeks of gestation
2% risk of miscarriage
What does MLPA stand for and what is it used for?
Multiplex Ligation-Dependent Probe Amplification
It is used to count the copy number for many exons at once.
What is the technique for MLPA?
use probes specific to each exon tested
each probe comes in 2 pieces
complete probe can only be formed in the presence of the complete and correct target sequence (DNA ligase)
probe is copied many times using PCR
amount of PCR product for each exon is compared to a ‘normal’ sample
What are stuffers?
attached to primers
made so that each product will be a different length and therefore can be separated by electrophoresis
