Flashcards in MGD mutations (session 9) Deck (21):
what causes mutations?
how does ionising radiation cause mutation? what is an example of ionising radiation?
UV radiation causes thymine dimmer formation
(UV causes bases on the same strand of DNA to bind to itself)
e.g. X-ray in diagnostic medicine
how does intercalating agents cause mutations?
intercalation of chemical IQ (ethidium bromide) between bases (forcing itself onto DNA strand), pushing bases apart, causing misreading by DNA polymerase, and therefore deletion of single base
how does tautomeric shift cause mutations?
a proton briefly changes position 'rare form' causing altered template base in DNA replication, therefore DNA polymerase attaches different complementary base (to rare form), only 25% being the complimentary base
how does DNA slippage cause mutations?
looping out of template or building strand to cause insertions or deletions
base loop out of new strand = 1 extra base in new strand
base loop out of template strand = 1 less base on new strand
what are the 2 different types of DNA damage that can occur?
single stranded damage
double stranded damage
what happens in single stranded damage repair for nucleotide excision repair? an example of this?
e.g. UV damage
removal of a longer region of damaged DNA and replacement
what happens in single stranded damage repair for mismatch repair?
patching up mistakes made by DNA polymerase
what happens in single stranded damage repair for base excision repair?
removes JUST the faulty base and replacing them
remove a nitrogenous base and replacing it
what are the 3 types of single stranded DNA damage repair?
nucleotide excision repair
base excision repair
what are the 3 types of double stranded DNA damage repair?
1. homologous recombination
2. non-homologous end joining (NHEJ)
3. microhomology-mediated end joining (MMEJ)
what is homologous repair in double stranded DNA damage?
using the other chromosome as a template for repair (in a pair of homologous chromosomes)
what is non-homologous end joining (NHEJ) repair in DNA damage?
ligation of the DNA breaks using micro-homologous regions
what is microhomology-mediated end joining (MMEJ)?
small homologous regions used to align DNA regions
what is a point mutation?
a single, isolated nucleotide base
what are the different types of point mutations?
what is nonsense mutation?
a single nucleotide mutation which results in the insertion of a stop codon in the transcript
what is missense mutation?
single nucleotide mutation which result in a change of amino acid
the effect of the change depends on the properties of the amino acids involved e.g. change on DNA or mRNA and which gene
what is silent mutation?
point mutations which have no effect on the amino acid coded
but can affect mRNA splicing introns --> can lead to heritable diseases
what is a transition mutation?
e.g. purine --> purine (2 rings - A & G)