MGD S9 - Mutagenesis Flashcards
How does a change in the base sequence of and nucleotide lead to a change in the primary sequence of a protein and what is the effect of this?
Change in genetic code (base sequence) can result in different amino acids being coded for.
This causes a change to the primary sequence of the protein which can lead to a change in shape and function of the protein.
What is a point mutation?
One base is substituted for another.
What is the difference between a transition and transversion point mutation?
Transition:
Purine swapped for another purine
Pyrimidine swapped for another pyrimidine
Transversion:
Purine swapped for a pyrimidine or Vice versa
What types of mutation can result from a point mutation in the coding region of a protein?
Silent mutations
Missense mutations
Nonsense mutations
What are the possible effect(s) of a point mutation in a non-coding region?
Altered binding sites
Altered promoter sequences
Altered splice sites
What are insertion or deletion mutations?
A sequence is added or removed for the nucleic acid.
How can insertion/deletion mutations vary in severity?
Give examples of multi-nucleotide deletion/insertion mutations of different severity
Single nucleotide base mutations
Few nucleotide mutations
E.g. Triplet repeats
Millions of nucleotide mutation
E.g. Tandem duplications
What is a frameshift mutation?
An insertion or deletion of a number of nucleotides not divisible by 3
This causes the shift of all subsequent triplet codes up one nucleotide
What is a silent mutation?
A mutation that doesn’t result in a different amino acid being specified
What is a Missense mutation?
A mutation that replaces one amino acid with another
What is a Nonsense mutation?
A mutation that results in a premature stop codon
What is a spontaneous mutation?
A mutation that is:
Not caused by exposure to a known mutagen
Can be due to errors in DNA replication
Can be due to DNA bases having a slight chemical instability
Why does the rate of spontaneous mutation differ between genes?
Depends on size of gene
Dependent on DNA sequence
Each new individual has multiple new mutations in their genetic code, why are most individuals unaffected?
Most are in non-coding regions due to chance
What is the cause of induced mutations?
Chemicals and radiation can be mutagenic, they cause mutation
What is a carcinogen?
A chemical that causes cancer
Give examples of mutagens and how they mutate the genetic code
Alkylating agents:
Remove a base
Acridine agents:
Add or remove a base
X rays:
Break chromosomes/delete a few nucleotides
UV radiation:
Creates thymine dimers
What is a Wild-type trait?
A trait that is the most common in a population
What is a mutant phenotype and what causes it?
Caused by a mutation
Mutant phenotype is a phenotype that differs from the most common/wild type trait in a population
What is a mutant allele and what causes it?
Caused by mutations to a gene
Mutant allele is an allele that differs from the common/wild-type allele in a population
What are the 3 modes of DNA repair?
Mismatch repair
Excision repair:
Nucleotide excision
Base excision repair
What is mismatch repair?
Occurs when enzymes detect nucleotides that don’t base pair in newly synthesised DNA
The incorrect base is excised and repaired
This process is also called proofreading
What is nucleotide excision repair and what type of damage does it repair?
Involved in the repair of larger/more bulky lesions to DNA that distort the Helix
Can replace 10 - 30 bases
What is base excision repair, how is it performed and what type of damage does it repair?
Takes two forms:
Short patch BER:
- One nucleotide replaced
Long Patch BER:
- 2 to 10 nucleotides replaced
The base is excised and replaced by DNA polymerase and DNA ligase