MGD mutations (session 9)

Question 1

what causes mutations?

Answer 1

ionising radiation
intercalating agents
DNA slippage
tautomeric shift

Question 2

how does ionising radiation cause mutation? what is an example of ionising radiation?

Answer 2

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

Question 3

how does intercalating agents cause mutations?

Answer 3

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

Question 4

how does tautomeric shift cause mutations?

Answer 4

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)

Question 5

how does DNA slippage cause mutations?

Answer 5

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

Question 6

what are the 2 different types of DNA damage that can occur?

Answer 6

single stranded damage

double stranded damage

Question 7

what happens in single stranded damage repair for nucleotide excision repair? an example of this?

Answer 7

e.g. UV damage

removal of a longer region of damaged DNA and replacement

Question 8

what happens in single stranded damage repair for mismatch repair?

Answer 8

patching up mistakes made by DNA polymerase

Question 9

what happens in single stranded damage repair for base excision repair?

Answer 9

removes JUST the faulty base and replacing them

remove a nitrogenous base and replacing it

Question 10

what are the 3 types of single stranded DNA damage repair?

Answer 10

nucleotide excision repair
mismatch repair
base excision repair

Question 11

what are the 3 types of double stranded DNA damage repair?

Answer 11

1. homologous recombination
2. non-homologous end joining (NHEJ)
3. microhomology-mediated end joining (MMEJ)

Question 12

what is homologous repair in double stranded DNA damage?

Answer 12

using the other chromosome as a template for repair (in a pair of homologous chromosomes)

Question 13

what is non-homologous end joining (NHEJ) repair in DNA damage?

Answer 13

ligation of the DNA breaks using micro-homologous regions

Question 14

what is microhomology-mediated end joining (MMEJ)?

Answer 14

small homologous regions used to align DNA regions

Question 15

what is a point mutation?

Answer 15

a single, isolated nucleotide base

Question 16

what are the different types of point mutations?

Answer 16

1. nonsense
2. missense
3. silent

Question 17

what is nonsense mutation?

Answer 17

a single nucleotide mutation which results in the insertion of a stop codon in the transcript

Question 18

what is missense mutation?

Answer 18

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

Question 19

what is silent mutation?

Answer 19

point mutations which have no effect on the amino acid coded

but can affect mRNA splicing introns –> can lead to heritable diseases

Question 20

what is a transition mutation?

Answer 20

e.g. purine –> purine (2 rings - A & G)

Question 21

what is a transversion mutation?

Answer 21

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