MGD mutations (session 9) Flashcards Preview

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what causes mutations?

ionising radiation
intercalating agents
DNA slippage
tautomeric shift


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
(proton moves)


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
mismatch 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?

1. nonsense
2. missense
2. silent


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)


what is a transversion mutation?

e.g. purine --> pyrimidine (1 ring - C,T,U)