Test2: Lect 7 Moore

Question 1

Two types of NHEJ?

- What does NHEJ stand for?

Answer 1

NHEJ (non-homology mediated end joining), and MMEJ (micro-homology mediated end joining)

Question 2

Process for NHEJ to occur, how does it differ from HRR?

Answer 2

NHEJ
->
Break
->
Ku binds break
->
53BP1 binds strand, it is highly phosphorylated in G1 and early S
->
It doesn't let go, BRCA1 binds, mediates end joining
- In HRR
HRR
->
Break
->
Ku binds break
->
53BP1 binds strand, it is only slightly phosphorylated in G2 and late S
->
It let's go, BRCA1 complexes with MRN, cuts the strand, resection, bind to the other strand.

Question 3

MMEJ:

• Stands for:
• differs from NHEJ?
• Similar to what?

Answer 3

- Stands for:
microhomology mediated end joining
- differs from NHEJ?
almost always causes deletions,
Uses resection
Requires homology
- Similar to what?
Single Strand Annealing (SSA)

Question 4

Four types of HRR?

- What does HRR stand for?

Answer 4

SSA (single strand annealing)
BIR (break induced repair)
SDSA (synthesis dependent strand annealing)
DSBR (double strand break repair)
- What does HRR stand for?
Homology recombination repair

Question 5

SSA:

• What happens?
• Requires?

Answer 5

The same thing as MMEJ, but different proteins.

1. A break occurs
2. Resection
3. Homologous regions align
4. Annealing (to sequence of some homology)
5. flap removal (the flap is any portion of the strand which overhangs the sequence of homology)
6. Ligate those puppies together
   - Requires?
7. Two homologous sequences nearby which are on the same gene

Question 6

BIR:

• Stands for?
• Features?
• Process?

Answer 6

• Stands for?
  Break induced repair
• Features?
  1. Occurs at the end of the strand, when the small segment is lost
  2. Results in homozygosity
  3. Tip is replaced with the sister chromatid
• Process?
  1. Break occurs near end of chromosome
  2. Tip is lost
  3. Remaining chromosome has two strands, strand 1 and strand 2
  4. Strand 1 invades neighboring sister chromatid
  5. Strand 1 is extended based on information from that chromatid
  6. Strand 2 is extended based on the information from strand 1

Question 7

SDSA stands for:

• Major pathway for repair during:
• Process:

Answer 7

Synthesis dependent strand annealing

• Major pathway for repair during:
  1. Mitosis
• Process:
  1. Double strand break
  2. 5’ to 3’ resection
  3. (D loop, displacement loop formation) Invasion of strand 1 into sister chromatid.
  4. New DNA is synthesized from templates for strand 1
  5. Strand 2 uses strand displaced by strand 1 as a template.
  6. Unwinding from template
  7. Ligation
  8. Once again loss of heterozygosity

Question 8

DSBR stands for:

• Process:
• Process specific:

Answer 8

Double Strand Break Repair

• Process:
  1. ds break.
  2. Resection 5’ – 3’ of both strands
  3. (D loop, displacement loop formation) Invasion of strand 1 into sister chromatid.
  4. Strand 2 uses strand displaced by strand 1 as a template.
  5. Synthesis
  6. Ligated
  7. Resolution
  a. Can occur with or without crossover
• Process specific:
  1. MRN, PARP, and BRCA1 et al recognize the break
  2. Exonuclease mediates the 5’ – 3’ resection
  3. RAD51 coats ssDNA
  4. RAD51 mediates invasion of homologous region with ssDNA
  5. D displacement loop formed
  6. Synthesis
  7. Resolution

Question 9

What roll does RAD51 have in:

i. Resection:
ii. Invasion:
iii. DNA synthesis:
iv. Resolution:

Answer 9

i. Resection: Coats exposed ssDNA during/after resection
ii. Invasion: Mediates invasion of strands
iii. DNA synthesis: RAD51 leaves, exposing 3’ OH for DNA synthesis
iv. Resolution: No role

Question 10

Name a specific disease caused by failure of recombination repair to do its upmost:

Answer 10

Fanconi Anemia

Question 11

Fanconi Anemia:

• How many genes can cause Fanconi Anemia?
• Symptoms?
• Inheritance?

Answer 11

• How many genes can cause Fanconi Anemia?
  1. 20+ genes
• Symptoms?
  1. Short stature, abnormal pigmentation, skeletal malformations of upper and lower limbs, microcephaly, ophthalmic and genitourinary anomalies
• Inheritance?
  1. Mostly recessive
  2. There are some dominant mutation, (which include a dominant RAD51 mutant)

Question 12

Fanconi Anemia:

- Factors at risk?

Answer 12

• Factors at risk?
  1. Bone marrow failure at less than 8 years old
  2. Risk of hematological disorders
  3. Cancer risk (500x more likely to get AML, 600x more likely for head and neck tumors)

Question 13

Fanconi Anemia:

- How is it tested for?

Answer 13

• How is it tested for?
  1. Acutely sensitive to interstrand crosslinking agents
  2. These cause replication fork stalling
  3. Makes unusual chromosomes
  4. Next generation seq panels for diagnosis

Question 14

NHEJ process in general:

Answer 14

Break occurs
Ku recruits kinases, which recruits DNA-PK which phosphorylates proteins.
Artemis aligns two strands bound
DNA ligase seals the wound.