Mutagenesis Flashcards
What is a silent mutation
A single base change which doesn’t change the amino acid
What is a missense mutation?
One amino acid substituted for another, normally by a single base change
What can a silent mutation cause?
It can disrupt RNA splicing and cause inheritable diseases
What is a nonsense mutation?
An amino acid codon is mutated to a stop codon
What is a frameshift mutation?
The reading frame of mRNA is altered by insertions, deletions, slice-site mutation
Not a multiple of three
What is a point mutation?
A base substitution
What is a transition point mutation?
When a purine is substituted for a purine. Same with pyrimidines
What is a transversion point mutation?
When a purine is changed for a pyrimidine and vice versa
How can a spontaneous mutation occur?
Error in DNA replication
DNA bases have slight chemical instability
What does the rate of spontaneous mutation depend on for different genes?
The size of the gene
The sequence
Give examples of chemicals that cause induced mutations and what change they can cause
Alkylating agents - remove a base
Acridine agents - add/remove a base
X-rays - break chromosomes or delete nucleotides
UV radiation - creates thymidine dimers
What is a mutation?
A change in a nucleic acid sequence, which can be the deletion, insertion, or rearrangement of one or many nucleotides.
What is a wild type?
An individual within a population displaying a wild type trait, which is the trait that is most common in that population
What is tautomeric shift?
When a proton briefly changes position in a base. It behaves as an altered template base during replication.
What pairs are joined in tautomeric forms?
C and A
T and G
What is mismatch repair?
Enzymes detect nucleotides which don’t base pair in newly replicated DNA.
The incorrect base pair is excised and replaced.
What is proof reading?
Detection of mismatched base pairs
What is excision repair?
Damaged DNA is removed by excision of bases and replacement is done by DNA polymerase
What is the different between nucleotide excision and base excision repair?
Nucleotide repair
- replaces up to 30 bases
- repair of UV damage and some carcinogens
Base repair
- replaces 1-5 bases
- repairs oxidative damage
What can tumour cells do? (6 things)
- Cells divide independently of external growth signals
- Ignore external anti-growth signals
- Avoid apoptosis because DNA is damaged so much
- Divide indefinitely without senescence
- Stimulate sustained angiogenesis
- Invade tissue and establish secondary tumours
What are oncogenes?
Genes involved in control of cell division. Can inhibit/stimulate growth
How can PCR be used in detecting mutations?
If the restriction site for a particular enzyme is destroyed by the mutation, then the mutated gene will have fewer fragments if digested with that enzyme, as it lacks the site.
In diagnosing genetic diseases, what is Southern blotting good for?
When there is a need to analyse larger segments in and around the gene and also for triple repeat disorders.
What is array-CGH good for?
Screen for sub-microscopic chromosomal deletions for which the locus cannot be determined by the patient’s phenotype.
