DNA Repair/Recombination

Question 1

Disease caused by a defect in the DNA repair pathway, nucleotide-excision repair. Unable to repair DNA damage by UV light, causing skin cancer.

Answer 1

Xeroderma Pigmentosum

Question 2

Three types of DNA repair involving excision and subsequent replacement

Answer 2

1) mismatch repair
2) nucleotide excision repair
3) base excision repair

Question 3

What protein helps mediate correct sequence determination in mismatch repair?

Answer 3

Mut proteins

Question 4

What causes Hereditary Nonpolyposis Colorectal Cancer (HNPCC), otherwise known as Lynch Syndrome?

Answer 4

Mutations in mismatch repair

Question 5

UV light can cause adjacent pyrimidine bases to do what?

Answer 5

dimerize

Question 6

Subtype of endonucleases used to repair pyrimidine dimers?

Answer 6

exinuclease

Question 7

How does exinuclease differ from endo/exonucleases?

Answer 7

It cuts with two nicks, not one.

Question 8

Two major reasons base-excision repair is needed

Answer 8

1) Spotaneous deamination of cytosine to uracil

2) deamination of adenine to hypoxanthine

Question 9

What is the enzyme which recognizes and removes uracil at the start of base excision repair?

Answer 9

uracil glycosylase

Question 10

For step 2 of base excision repair, what enzyme nicks the backbone of the damaged strand at the missing base (apyrimidinic site)?

Answer 10

AP endonuclease

Question 11

For step 3 of base excision repair, which enzyme removes the base free phosphate residue

Answer 11

Deoxyribose phosphate lyase

Question 12

Which DNA Polymerase fills the gap in base excision repair?

Answer 12

DNA Polymerase I

Question 13

How does ricin act on DNA or RNA

Answer 13

Depurination of rRNA

Question 14

What’s the problem if guanine is methylated to O6-Methylguanine?

Answer 14

It messes up its hydrogen bonding

Question 15

Which DNA repair mechanism does not involve DNA polymerase?

Answer 15

Direct repair

Question 16

What process is responsible for correcting pyrimidine dimers in bacteria?

Answer 16

Photoreactivation

Question 17

In direct repair, what enzyme converts O6-methylguanine back into regular guanine

Answer 17

methyltransferase

Question 18

What are the two mechanisms for double stranded break repair?

Answer 18

1) Nonhomologous end-joining repair (NHEJ)

2) Homologous recombination repair (HR)

Question 19

What causes a need for double stranded break repair?

Answer 19

High-energy radiation and oxidative free radicals

Question 20

Which of the two double stranded break repair is more error prone?

Answer 20

Nonhomologous end-joining repair

Question 21

The BRCA1 and BRCA2 genes are involved in what process?

Answer 21

homologous recombination repair

Question 22

How does homologous recombination repair work?

Answer 22

Uses the same machinery/enzymes as homologous recombination in meiosis. It’s availability depends on the stage of the cell cycle

Question 23

DNA recombination in which it occurs at aligned points on the genetic map so that no information is lost.

Answer 23

Legitimate recombination

Question 24

Fidelity of DNA is not preserved. Recombination occurs between DNA segments not aligned on the genetic maps.

Answer 24

Illegitimate recombination

Question 25

Crossing over of homologous chromosomes, leading to the switching of genetic material between them.

Answer 25

Holliday junction

Question 26

The movement of transposons from one site to another is an example of...

Answer 26

illegitimate recombination

Question 27

What type of transposon is known to cause many human diseases?

Answer 27

the movement of Alu sequences