Chapter 2 (DNA replication And Repair)

Question 1

3’ exonuclease function ?

Answer 1

Removing mispaired deoxynucleotides during DNA synthesis ( DNA repair )

Question 2

5’ exonuclease function ?

Answer 2

Removing RNA primer at the end of DNA synthesis

Question 3

Azt mechanism ?

Answer 3

Inhibit reverse transcriptase in retroviruses (HIV)

Question 4

Etoposide and teniposide mechanisms ?

Answer 4

Inhibits DNA topoisomerase ll in eukaryotic cells leading to oversupercoiling and eradication of cancer cells

Question 5

Quinolones and fluoroquinolones mechanism ?

Answer 5

Inhibit DNA gyrase ( topoisomerase ll ) in prokaryotic cells and most active against aerobic grame -ve bacteria

Question 6

Which enzyme is deficient in Xeroderma pigmentosum ?

Answer 6

Excision endonuclease which recognizes and excise thymine dimers in G1

Question 7

Mutation of what genes causes Lynch syndrome ?

Answer 7

hMSH2 or hMLH1 which recognize and excise mismatched bases in G2

Question 8

P 53 gene ?

Answer 8

Encodes a protein that prevent a cell with damaged DNA from entering S phase , it’s mutation leads to Li Fraumeni syndrome and many solid tumors

Question 9

ATM gene ?

Answer 9

Encodes a kinase essential for P 53 gene , it’s mutation leads to ataxia telangectasia which leads to Lymphomas

Question 10

Uracil glycosylase enzyme ?

Answer 10

Repair cytosine deamination errors by excision of the resultant uracil base

Question 11

Xeroderma pigmentosum ?

Answer 11

Autosomal recessive
Due to excision endonuclease deficiency
Leads to carcinoma and melanoma early in life
Diagnosed by : measurement of excision endonuclease in WBCs

Question 12

Diagnostics tool of Lynch syndrome ( hereditary nonpolyposis colorectal cancer ?

Answer 12

Searching for microsatellite instability in cells resected from the tumor

Question 13

Lagging strand ?

Answer 13

Strand during DNA replication which is synthesized discontinuously as a series of small fragments ( Okazaki fragments )

Question 14

DNA gyrase ( DNA topoisomerase ll ) function ?

Answer 14

Removal of the positive supercoils ahead of advancing replication forks

Question 15

Disease associated with decreased Telomerase activity ?

Answer 15

Progeria ( reversed aging )

Question 16

First tumor suppressor gene to be cloned ? It function ?

Answer 16

Retinoblastoma Rb gene
Negative regulator of the cell cycle through its ability to bind the transcription factor E2F and repress transcription of genes required for S phase