Mutagenesis Flashcards
What does a change in genetic code result in?
Different amino acids being coded for
What does a change in primary sequence result in?
Change in shape, and therefore function, of a protein
What are point mutations?
Base mutations - transition or transversion (silent, missense, nonsense if in the coding region of the protein)
What is the result of a point mutation that is not in the coding region of a protein?
Alteration of binding sites, promoter sequences, splice sites etc
What is a frameshift mutation?
Addition or subtraction of nucleotides not in multiples of 3
What is a silent mutation?
A mutation that doesn’t alter the amino acid specified and thus doesn’t alter the sequence
What is a missense mutation?
A mutation that replaces one amino acid with another
What is a nonsense mutation?
A mutation that changed the amino acid specified to a stop codon
What is a spontaneous mutation?
Not caused by exposure to a known mutagen, errors in DNA replication, DNA bases have slight chemical instability
What determines the rate of spontaneous mutations in genes?
Size and sequence
What are induced mutations?
Mutations cause by chemicals (mutagens) or cancers caused by chemicals (carcinogens)
What do alkylating agents do?
Remove a base
What do acridine agents do?
Add or remove a base
What do X-rays do?
Break chromosomes/delete a few nucleotides
What does UV do?
B- produces vitamin D, B/C - destroy vitamin A, A/B/C - damage to collagen fibres. Creates thymidine dimers
What is mismatch repair?
Enzymes detect nucleotides that don’t base pair in newly replicated DNA. Incorrect base is excised and replaced. Detection of mismatches is called proofreading
What is excision repair?
Damaged DNA is removed by excision of bases and replacement by DNA polymerase
What does nucleotide excision do?
Replaces up to 30 bases and is used in repair of UV damage and some carcinogens
What does base excision do?
Replaces 1-5 bases and repairs oxidative damage
What is p53 and what is its function?
It’s a protein that monitors the repair of damaged DNA and if it’s too damaged then it promotes apoptosis.
How are tumours formed?
Derived from individual abnormal cells, arise from lack of normal growth control, multistep process, more likely to arise in cells undergoing frequent cell division, same type
What are oncogenes?
Genes involved in the control of cell division. Present in normal cells, many different classes may stimulate/inhibit growth.
What do tumour suppressor genes do?
Genes involved in protecting the cell against one step on the path to cancer
How do oncogenes arise?
In cells they are usually proto-oncogenes. When they are mutated they become oncogenes
