Mutations Flashcards
(34 cards)
What does SNPs stand for?
Single nucleotide polymorphism
Happens when single base substituted for another
List the types of mutational changes that can occur (4 main)
Base substitution Deletions Insertions Rearrangements Splice site mutation
What is a transitions mutation?
Transition- change of base but still same type of base
Eg purine–> purine
Or Pyrimidine–> Pyrimidine
What is a transversion mutation? How does this differ from transition?
A purine base changes to a Pyrimidine or vice versa
Transition stays as the same type (A and G)
Which is more common- transition or transversion mutations?
Transition (same type eg still purine)
In brief, how can mutations come about?
Spontaneously or induced (due to mutagen)
What is the difference between a missense and nonsense mutation?
Missense- results in an amino acid change
Nonsense- results in amino acid change to a stop codon
What is a silent mutation? Do they have any effect?
A nucleotide change which causes no change in the amino acid it codes for
These are most often the 3rd nucleotide in a Triplet
- can affect RNA splicing if mutation occurs at a splice site
What is a missense mutation? Does it have any effect?
A mutation that results in the substitution of one amino acid for another
Yes- could effect tertiary structure of protein
What is a frame shift mutation? How do they come about?
Where 1 or 2 nucleotides have been deleted or inserted and so shifts the reading frame
How do frame shift mutations cause problems?
- As its a frame shift every codon will be altered and read differently therefore every amino acid could be different
- Also often new stop codons are found- TF premature termination
What is a PTC (premature termination codon)?
Where a frame shift mutation has occurred leading to the formation of a new stop codon
What happens to PTC’s?
Degraded by nonsense mediated decay
TF little or no protein is produced as a result
List 3 general causes of mutations
During DNA replication
Chemical mutagens
Radiation exposure
What changes can occur during DNA replication which can lead to mutations? Describe them
Tautomeric shift- proton changes position briefly forming rare form which affects pairing properties
Strand slippage- on new strand- extra nucleotide added. On template- one less nucleotide
List 3 ways chemical mutagen can cause mutations
Directly- nitrous acid changes amino to keto group
- EMS remove purine ring TF RNA polymerase adds in any random base (3/4 times its wrong)
Indirectly- molecule forces itself between bases TF they’re further away and can’t be read
What is thymine dimer formation?
UV photons cause adjacent thymines to pair- breaking the DNA double strand shape
Can occur with any Pyrimidine base
What are the two purine bases? How many ‘rings’ do they have?
Adenine
Guanine
TWO!!!
What are the two Pyrimidine bases? How many ‘rings’ do they have?
Thymine
Cytosine
ONE!!
List the ways homozygosity can occur (4)
Mitotic recombination
Point mutation
Deletion (of wild type/normal gene)
Loss of wild type chromosome (v. rare- TF only mutated is present)
Who is more likely to develop cancerous cells- someone with or without one inherited mutation? Why?
Someone who already has 1 mutated allele
They are more likely to get the two mutated alleles as they only need one more, whereas someone without needs two mutated alleles before developing cancerous cells.
What is the most common form of mutation?
Single base substitution- SNPs
Single nucleotide polymorphism
List methods of DNA repair (4)
Say if they occur before or after replication
99%- DNA polymerase fixes error- before
Nucleotide mismatch repair- after
Excision repair- after
Double stranded break repair- after
What happens in nucleotide mismatch repair?
An enzyme detects mismatched base in newly synthesised strand
Patch of DNA surrounding error is replaced
Erroneous base replaced with correct one
