Session 9 Flashcards
What is a transition mutation?
A point mutation where’s purine is substituted for another purine, or a pyrimidine is substituted for another pyrimidine.
Which is more common, a transition or transversion mutation?
Transition mutation.
A change in which base position is most likely to cause a silent mutation?
The third codon position.
What is a missense mutation?
A mutation where one amino acid is substituted for another, usually because of a single base change.
What is a silent mutation?
Mutation where a single base change doesn’t cause a change in amino acid.
How can silent mutations cause heritable diseases?
They may disrupt RNA splicing.
What is a nonsense mutation?
Mutation where an amino acid codon is mutated to a stop codon.
What is a frameshift mutation?
Mutation where the reading frame of mRNA is altered. May be due to insertion, deletion, or splice-site mutation.
What is a conservative missense mutation?
Change in amino acid due to mutation that can be tolerated.
What size of insertion/deletion doesn’t cause a shift in reading frame?
An insertion/deletion which is 3bp or multiples of 3bp.
What causes base changes?
- Sequence changes during DNA replication
- Chemical-induced mutation
- Exposure to different types of radiation
What is tautomeric shift? Why can it be problematic?
Brief change in the position of a proton in a DNA base.
Causes the base to have altered pairing properties: may cause anomalous base pairing.
How can mis-paired DNA bases be repaired?
DNA polymerase detects the mispairing in the newly synthesised strand and corrects it 99% of the time.
Enzymes can detect mismatched bases and replace them by replacing a patch of the DNA sequence.
How are damaged bases repaired?
Replaced via excision repair: the damaged base (and sometimes the bases around it) are excised and replaced with undamaged ones.
What can failure to repair DNA lead to?
Cancers
