DNA mutation & repair

Question 1

What are chromosomal (large scale) DNA damages?

Answer 1

large double stranded breaks, translocations, aneuploidy (unusual chromosome number)

Question 2

MSH2, 3, 6, MLH1, PMS2

Answer 2

colon cancer, mismatch repair

Question 3

Xeroderma pismentosum (Xp)

Answer 3

skin cancer, UV sensitivity, neuro abnormalities. a genetically heterogeneous, autosomal recessive disease of defective DNA repair. mutations are found in genes that mediate NER

Question 4

ataxia telangiectasia (AT)

Answer 4

leukemia, lymphoma, gamma ray sensitivity

Question 5

BRCA2

Answer 5

breast, ovarian, prostate cancer

Question 6

Werner syyndrome

Answer 6

premature aging

Question 7

What is benzo[a]pyrene?

Answer 7

carcinogen produced by cigarette smoke, not carcinogenic until it is oxidized within cells, then it binds covalently to guanine. G to A transition mutations. a common target is the p53 tumor suppressor gene that is mutant in most cancers, especially lung cancers

Question 8

ultraviolet rays from the sun does what?

Answer 8

exciting adjacent pyrimidine bases, causing them to form covalent dimers, Thymine dimer. sometimes C

Question 9

Steps in single stranded mutation repair?

Answer 9

endo and exonucleases removes region , repair dna polymerase adds, dna ligase = repaired

Question 10

summary of spontaneous alterations likely to require DNA repair? what are example?

Answer 10

oxidative damage, hydrolytic attack , and uncontrolled methylation. depurination and deamination C>U

Question 11

what is the result of depurination if uncorrected?

Answer 11

encounters a missing purine + deletion. DNA polymerase fixes

Question 12

what is MutS and MutL

Answer 12

MutS binds specifically to a mismatched base pair, while MutL scans the nearby DNA for a nick.

Question 13

HNPCC (hereditary non-polyposis colorectal cancer)…. whats the defect?

Answer 13

MLH1, one mutant and one normal, then cancer makes the normal one mutant by epimutation. epigenetic mutation silence the normal one

Question 14

Pathway of base excision repair?

Answer 14

dna glycosylase, AP endonuclease and phosphodiesterase, DNA polymerase and DNA ligase. remove a single base

Question 15

explain the nucleotide excision repair?

Answer 15

TFIIH helicase subunit, a nuclease, polymerase, ligase), dna helicase. removes longer streches of bases

Question 16

double-strand break repair

Answer 16

repair of ds breaks is nonhomologous end-joining, which involves joining the broken ends together by DNA ligation, but which also results in loss of some nucleotides or homologous end-joining, which utilizes the other undamaged homologous chromosome

Question 17

Nonhomologous end-joining?

Answer 17

end-joining alters the original DNA sequence when repairing broken chromosomes. These alterations can be either deletions (as shown) or short insertions.

Question 18

homologous recombination, what are the major proteins?

Answer 18

involves a genetic exchange between a pair of homologous DNA sequences for repair of mistakes. very precise. RecA (prokaryotes)/Rad51 (humans) proteins

Question 19

crossing over requires an extensive region of sequence homology and recognition occurs during a process called ?

Answer 19

DNA synapsis

Question 20

what is the key cell sensor when responding to DNA damage.

Answer 20

ATM

Question 21

an important G1 checkpoint control gene?

Answer 21

p53, cancer when mutated and no regulation of synthesis

Question 22

unusual chromosome number, non-dysjunction?

Answer 22

aneuploidy