Sollars - DNA Repair and Recombination

Question 1

Types of repair involving excision and replacement

Answer 1

Mismatch Nucleotide excision Base exchange

Question 2

What does Mismatch Repair preserve?

Answer 2

Fidelity

Question 3

When does Mismatch repair occur?

How is the correct strand recognized?

What can result when it’s broken?

Answer 3

Repairs errors after replication

DNA methylation makes the correct strand

HNPCC (Lynch Syndrome) can result when broken

Question 4

What does Nucleotide Excision Repair fix?

What can a defect in Excinuclease result it?

Answer 4

Repairs damage resulting from large distortions in the DNA double helix.

Defect in excinuclease can result in Xeroderma Pigmentosum

Question 5

What can UV light do to DNA?

What repair system corrects this?

Answer 5

Can cause pyrimidine dimers–adjacent thymines dimerize.

Nucleotide Excision Repair fixes this.

Question 6

What does DNA contain thymine, not uracil?

Answer 6

Cytosine can spontaneously convert to Uracil, and you would have C-G, A-U. Would throw off repair systems with no way to dope the scope.

Question 7

What creats an abasic site in DNA, and much slower in ribonucleotides and RNA?

Answer 7

Depurination

Question 8

How does Ricin work?

Answer 8

Depurination of RNA

Question 9

Base-Excision Repair

What comes through and fixes the last step?

Answer 9

Repairs altered bases resulting from spontaneous changes and environmental stress (deamination, depurination)

Produces an apyrimdinic site that needs to be repaired (gap in the chain)

Deoxyribose Phosphate Lyase removes the base free phosphate, and DNA Polymerase and DNA Ligase fill in the gap

Question 10

What is the most common single base mutation in human cancer?

What can remove the incorrect methyl markers?

Answer 10

C to T or G to A

Base Excision Repair

Question 11

Direct Repair

Answer 11

Specific enzymes are dedicated to repairing specific DNA damage; following use will be “inactive” and degraded.

Question 12

Double Stranded Break Repair

Cause?

NHEJ?

HR?

Experimental Use?

Answer 12

Cause: High energy radiation and oxidative free radicals

NHEJ = Nonhomologous end-joining (NHEJ) repair; uses different DNA strand to repair; more error prone!

HR = Homologous Recombination (HR); BRCA1/BRCA2; may signal breast cancer risk if abnormal BRCA

Use: CRISPR

Question 13

DNA Recombination

Answer 13

Rearrangement or exhange of genetic information b/t two DNA molecules of b/t two different parts of the same DNA molecule

Question 14

Legitimate DNA Recombination

What type of junction is formed?

When is it most commonly seen?

Answer 14

Fidelity is preserved, event occurs at aligned points on genetic map, no information is lost, regions of high homology

Holliday Junction

Meiosis

Question 15

illegitimate Recombination

Answer 15

Fidelity is not preserved; recombination occurs between segments not aligned on the map.

Ex: Unequal Crossing Over

Question 16

Viral Integration

Answer 16

Example of illegitimate DNA recombination; some are site specific, others not.

HIV is not site specific

Question 17

Movement of Transposons

Answer 17

Example of illegitimate DNA recombination, over 1-million Alu sequences through genome, some disruptions can cause disease if transposon is inserted where it would disrupt another gene