4. DNA Repair

Question 0

salmonella typhimurium

Answer 0

has a mutation in the pathway of histidine biosynthesis

Question 1

Ames Test

Answer 1

shows rate of back-mutation

mutations escaping proof reading function of DNA pol III

Question 2

back-mutation

Answer 2

allows original mutation to be reversed

Question 3

mistmatch accidents

Answer 3

mismatch of base pairs

recognized shortly after synthesis & early enough to fix

Question 4

spontaneous alterations example

Answer 4

introduction of hydroxyl groups on double bonds or ribose ring

Question 5

hydrolytic attack examples (3)

Answer 5

1. depurination
2. depyrimidation
3. deamination

Question 6

4 examples of deaminations

Answer 6

1. adenine to hypoxathine
2. methylcytosine to thymine
3. cytosine to uracil
4. guanine to xanthine

Question 7

most frequent mutation?

Answer 7

depurination & deamination

Question 8

depurination results in?

Answer 8

deletion of the nucleotide whre the base left, leaving a point mutation

if in germ cell, problem passed to offspring
if in somatic cell, outcome can range from nothing to cancer

Question 9

uncontrolled methylation

Answer 9

mutation where SAM transfers methyl groups

Question 10

UV induced pyrimidine dimers

Answer 10

2 adjacent thymine bases dimerize, creating a kink in the DNA strand

recognized by DNA binding proteins to promote repairs

Question 11

mistmatch repair mechanism

Answer 11

mismatched base, DAM methylase methylates daughter strand (so parent strand can be distinguishable)

MutS & MutI bind DNA & form a complex

two MutH bind the complex and pull DNA through complex to cleave unmethylated strand

DNA pol III adds new nucleotides

DNA ligase seals

Question 12

base excision repair

Answer 12

used for deamination of cytosine to uracil

Question 13

DNA glycosylase

Answer 13

recognizes and removes incorrect base

Question 14

endonuclease & phosphodiesterase

Answer 14

removes sugar phosphate backbone

Question 15

DNA pol

Answer 15

removes several nucleotides using its exonuclease activity (5’ to 3’) and then immediately replaces them all the way to the nick

Question 16

DNA ligase

Answer 16

seals

Question 17

nucleotide excision repair

Answer 17

used for thymine dimers/pyrimidine dimers

exinuclease will bind to DNA at site of damage and cleave the damaged strand 29 nucleotides apart

helicase: removes cut segment

DNA pol: fills gap

DNA ligase: seals

Question 18

double-stranded repair: non-homologous end joining

Answer 18

repairs dsDNA in somatic cells; induces apoptosis in germ cells

break recognized by Ku proteins that recruit additional proteins for processing of DNA ends

proteins degrade nucelotides until both sides are blunt

results in loss of portion of DNA sequence

Question 19

homologous recombination

Answer 19

very accurate, NO LOSS of sequences

ONLY during S & G2 (w/sister chromatids)

recombinase activity

uses sister chromatid as template to repair its own strand

Question 20

BRCA1

Answer 20

found in replicating heterochromatic DNA

induces repair and has high affinity for double stranded breaks in DNA

Question 21

homozygous BRCA1-/BRCA1-

Answer 21

inability to repair DNA

leads to activation of P53

Question 22

P53

Answer 22

when activated, induces apoptosis

tumor suppressor gene

Question 23

colon cancer

Answer 23

defect in mismatch pair

defect in protein that detects base mismatches

Question 24

xeroderma pigmentosum (XP)

Answer 24

skin cancer with severe UV insensitivity

mutation in nucleotide excision repair used to remove thymine dimers

Question 25

BRCA2

Answer 25

breast, ovarian, prostate cancer

defect in repair of homologous recombination