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Radiation Biology > Chapter 2 Molecular Mechanism of DNA damage and Repair > Flashcards

Chapter 2 Molecular Mechanism of DNA damage and Repair Flashcards

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1
Q

Name 2 single ringed pyrimidines and 2 double ringed purines?
Name complement base pairs?

A

Thymine and Cytosine
Adenine and Guanine

Adenine_=Thymine
Guanine=Cytosine

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2
Q

Number of DNA lesions per cell detected immediately after X-ray D0 dose(between 1-2Gy) in mammalian cells?
Base ?
SSBs ?
DSBs ?

A

1000
1000
40

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3
Q

Define D0?

A

Dose of radiation that induce average of one lethal event per cell that leaves 37% still viable.

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4
Q

Define DSBs?

A

Break in two strands are opposite one another or separated by only few base pairs.

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5
Q

Diameter, energy and number of ion pairs in Spur and Blobs?

How much is the diameter of DNA double helix?

A

Spur 4nm/ 100eV / 3 ion pairs
Blobs 7nm / 100-500eV / 12 ion pairs

2nm

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6
Q

In X-rays and gamma rays, 95% of energy deposition event takes place in which form?

In densely ionizing radiations, Neutron and alpha-particles, greater proportion of energy deposition event takes place in which form?

A

Spur

Blobs

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7
Q

Clustered lesion could spread out up to how many base pairs?

A

20 base pairs

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8
Q

Which method is most widely used to measure DNA strand breaks?

A

Pulsed-Field Gel Electrophoresis(PFGE)

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9
Q

What does PGFE detect?

A

Induction and repair of DNA DSBs

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10
Q

What is advantageous of Single-cell Electrophoresis(Comet assay)?

A

Biopsy specimen from tumors in which a relatively small number of cells can be assayed to determine DNA damage and repair.

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11
Q

What does comet assay detect?

A

High sensitivity and specificity for SSBs and alkaline sensitive sites
Lesser degree to DNA DSBs

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12
Q

Name 6 assayed proteins for foci formation in DNA damage-induced nuclear foci assay(radiation-induced foci assay)

A 
H2AX - most common 
53BP1 - most common
ATM(Ataxia telangiectasia mutated)
RPA(Replication Protein A)
RDA51
BRCA1
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13
Q

Name enzymes used in following steps of Base Excision Repair

  1. Removal of sugar residue?
  2. Replacement with correct nucleotide?
  3. Completed by?
A
  1. Apurinic endonuclease 1(APE1)
  2. DNA polymerase
  3. DNA ligase III - XRCC1(X-ray cross complementing factor 1 gene)mediated ligation
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14
Q

Name enzymes used in repair of more than one nucleotide in Base Excision Repair

  1. Removal of sugar residue?
  2. Repair synthesis?
  3. Removal of overhanging flap structure?
  4. Completed by?
A
  1. APE1
  2. Complex of replication factor C(RFC)/proliferating cell nuclear antigen(PCNA)/DNA polymerase
  3. Flap endonuclease 1 (FEN 1)
  4. DNA ligase I
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15
Q

Name 2 pathways of nucleotide excision repair?

A

Global Genome Repair(GGR or GG-NER)

Transcription-Coupled Repair(TCR or TC-NER)

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16
Q

How does GG-NER and TC-NER differ in mechanism of NER?

A

Differs at initial damage recognition step

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17
Q

How does GGR recognize lesion?

A

Through XPC-XPE complex
XPC xeroderma pigmentosum complementation group C
XPE xeroderma pigmentosum complementation group E

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18
Q

How does TCR recognize lesion?

A

NER proteins are recruited by the stalled RNA polymerase in cooperation with CSB and CSA
CSB Cockayne Syndrome B gene
CBA Cockayne Syndrome A gene

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19
Q

Name 5 essential steps in pathway of NER?

A
  1. Damage recognition
  2. DNA incisions that bracket lesion, usually between 24-32 nucleotides in length
  3. Removal of region containing the adducts
  4. Repair synthesis to fill in the gap region
  5. DNA ligation
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20
Q

Name the enzyme that incise DNA lesion in NER?

Germline mutations in NER gene lead to which human DNA repair deficiency disorder?

A

XPG and XPF-ERCC1 endonuclease
XPG/XPF Xeroderma Pigmentosum complementation group G/F
ERCC1 Excision Repair Cross Complementation group 1 gene

Xeroderma Pigmentosum

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21
Q

Name the enzyme that fills gap at incised region in NER?

A

Polymerase aided by RFC and PCNA
RFC Replication Factor C
PCNA Proliferating Cell Nuclear Antigen

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22
Q

Name 2 types of DNA double strand break repair

A

Homologous Recombination Repair(HRR)

Non Homologous End-Joining(NHEJ)

23
Q

HRR occurs in which phase of cell cycle and why?

A

Late S/G2 phase

Because undamaged sister chromatid is available to act as template (before mitosis)

24
Q

NHEJ occurs in which phase of the cell cycle?

A

G1 phase

It has been found to be active in late S and G2 phase of cell cycle, is yet to identify cause!

25
Q

Which is prone to error in between HRR and NHEJ?

A

NHEJ, accounts for many premutagenic lesions

26
Q

Name protein kinase which act as sensor in immediate response of cell to DNA DSB?

A

APR(ATM and Rad3-related) belongs to PIKK(Phosphotidylinositol-3-Kinase related Kinase) family

27
Q

Name the protein that regulates competition for repair by HRR vs NHEJ?

A

53BP-1

28
Q

Describe 5 essential steps of NHEJ?

A
  1. End recognition by Ku binding
  2. Recruitment of DNA dependent protein kinase catalytic subunit (DNA-PKcs)
  3. End processing
  4. Fill-in-synthesis or end bridging(DNA Polymerase)
  5. Ligation(Ligase 4)
29
Q

Name key protein in HRR which mediates invasion of homologous strand of sister chromatid leading to formation of Holliday junction?

A

RAD51

30
Q

Name the combination repair pathways needed to repair DNA crosslinks

A

NER and HRR

31
Q

Name the disease hypersensitive to crosslinking agent?

A

Fanconi Anemia

32
Q

Describe 4 essential steps of Mismatch Repair?

A
  1. Mismatch identified by sensor
  2. MMR factors recruited
  3. Newly synthesized strand harboring mismatch identified and incorrect/altered nucleotides are excised
  4. Resynthesis and ligation of excised DNA tract completed
33
Q

Name the cancer due to mutation in mismatch repair genes?

A

HNPCC(Hereditary Nonpolyposis Colon Cancer)

34
Q

Enumerate essential features in Interphase of cell cycle

A

Largest phase of cell cycle
Quantity of DNA in nucleus doubles
Presence of nuclear membrane
Presence of nucleoli

35
Q

Enumerate essential features of prophase in cell cycle

A

Thickening of chromatin and increased stainability of chromosome
Chromosome has centromere
Nuclear membrane disappears
Nucleoli disappears

36
Q

Enumerate essential features of Metaphase in cell cycle

A

Chromosome move to cells equator
Spindles appears
Centromere divides

37
Q

Enumerate essential features of Anaphase in cell cycle

A

Movement of chromosome towards the pole

38
Q

Enumerate essential features of Telophase in cell cycle

A

Chromosome at poles begins to uncoil
Nuclear membrane reappears
Nucleoli reappears

39
Q

Define the role of telomere

A

It cap and protect the terminal ends of chromosome

40
Q

What comprise of base repeats in mammalian telomere?

A

TTAGGG in 1.5 to 150 kilobases

41
Q

After how many cell divisions does telomeric DNA is lost to undergo senescence?

A

40-60 cell divisions

42
Q

In hypothesis,Immortalization and carcinogenesis are associated with expression of what enzyme?

A

Telomerase

43
Q

What are 2 classes of radiation induced aberrations seen in metaphase?

A

Chromosome aberration

Chromatid aberration

44
Q

Chromosome aberration occurs in what phase of cell cycle?

A

Early in interphase before chromosome material has been duplicated

45
Q

Chromatid aberration occurs in which phase of cell cycle?

A

Later in interphase after DNA material has doubled and chromosome consists of two strands of chromatin

46
Q

Name 3 lethal and 2 non-lethal examples of radiation induced aberration

A

Dicentric(grossly distorted chromosome with 2 centromere)
Ring
Anaphase bridge

Symmetric translocation
Small interstitial deletion

47
Q

Ring aberration and Anaplastic bridge falls under which class of radiation induced aberration?

A

Ring - Chromosome aberration

Anaplastic - Chromatid aberration

48
Q

Symmetric translocation is observed in which technique of preparation?

A

FISH or chromosomal painting

49
Q

Name disease associated with symmetric translocation

A

Burkitt lymphoma

Leukemia

50
Q

What is widely used biomarkers of radiation exposure?

A

Chromosome aberration in peripheral lymphocyte

51
Q

Give an example of unstable aberration that decline with time after irradiation

A

Dicentric aberration

52
Q

Give an example of stable aberration that persist for many years and pass on aberration to their progeny

A

Symmetric translocation

53
Q

Two strands of DNA are joined by which bond?

A

Hydrogen bond

Radiation Biology (2 decks)

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