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Radiation Biology > Ali Questions > Flashcards

Ali Questions Flashcards

1
Q

Why ataxia-telangiectasia patiens are more sensitive to radiation?

A

Defective ATM
which is an improtant DNA damage kinase.

DNA Repair I - Floyd

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2
Q

What are the sources of DNA damage?

A
  1. endogenous agents (~500K events/day):
    - Metabolism byproducts (base damage)
    - Free radicals (base damage, strand breaks)
  2. exogenous Agents
    - ionizing radiation (all kinds: bulky, base, strand breaks)
    - chemicals (all kinds: alkylation, strand breaks)
  3. Normal processes
    - immune system diversity (double strand breaks, mismatch, and base excision)
    - Meiosis (double strand breaks)
    - replication problems (mismatch error, stalled forks, strand breaks)

DNA Repair I - Floyd

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3
Q

Radiation kills tumor cells by which types of DNA damages?
Which one is the most lethal?

A
  1. Breaks:
    SSBs
    DSBs
  2. Base damages:
    change
    loss (abasic sites)
  3. crosslinks
    DNA-DNA
    DNA-protein

DNA Repair I - Floyd

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4
Q

Approximately how many DSBs/cell/Gy of radiation happens?

A

30-50 DSBs
compare to:
~1K SSBs, ~1K sugar damage, ~1K-2K base damage, loss or substitution
~100-200 DNA-protein crosslinks
~30 DNA-DNA crosslinks

DNA Repair I - Floyd

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5
Q

What are DNA damage repair pathways in response to double strand breaks?
Which one is error prone?
When in the cell cycle which one happens?

A
  1. Non-homologous end joining (NHEJ)
    - error-prone
    - G0/G1 phases of cell cylce (no sister chromatid)
  2. Homologous recombination repair (HRR)
    - “high fidelity” template directed
    - S/G2 phases of cell cycle
  3. Microhomology-Medicated End Joining (MMEJ)

DNA Repair I - Floyd

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6
Q

Which proteins are involved in NHEJ?

A

Ku70/Ku80
DNApk
Artemis
ATM
gamma H2AX

DNA Repair I - Floyd

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7
Q

Which proteins are involved in homologous recombination?

A

ATM
BRCA1, BRCA2
RAD51

DNA repair I - Floyd

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8
Q

What are Holiday junctions and they are formed durign what type of DNA repair?

A

Homologous recombination

DNA repair I - Floyd

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9
Q

Which enzyme performs 5’ -> 3’ resection during homologous recombination?

A

MRX

DNA repair I - Floyd

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10
Q

What is patients with xeroderma pigmentosa are sensitive to? Why?

A

Ultraviolet light
DNA damage repair dysfunction that distorts the helix.
Nucleotide excision repair (NER)

DNA repair I - Floyd

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11
Q

What are the different types of single strand break repairs? Which lesions each one repair?

A
  1. Base excision repair (BER)
    oxidized, alkylated, deaminated bases, or uracil
  2. Nucleotide excisino repair (NER)
    cyclobutane pyrimidine dimers, photoproducts
  3. Mismatch repair
    repair of G/T and A/C pairs

DNA repair I - Floyd

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12
Q

What are the key molecules involved in these parts of NHEJ?

  1. Mistake recognition
  2. Mistake excision
  3. Mistake repair
A
  1. Mistake recognition
    Ku70/Ku80
    DNA-PKcs
  2. Mistake excision
    DNA-PKcs
    Artemis
  3. Mistake repair
    Pol gamm/mu
    XRCC4
    Ligase IV

DNA repair I - Floyd

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13
Q

What are the key molecules involved in these parts of homologus recombination?

  1. Mistake recognition
  2. Mistake excision
  3. Mistake repair
A
  1. Mistake recognition
    MRN complex
    FANC proteines
  2. Mistake excision
    ATM
    BRCA1/BARD1
    MRN complex
    RPA
    PALB2
    BRCA2
    RAD51
    CtlP
  3. Mistake repair
    DNA polymerases

DNA repair I - Floyd

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14
Q

What are the key molecules involved in these parts of mismatch repair?

  1. Mistake recognition
  2. Mistake excision
  3. Mistake repair
A
  1. Mistake recognition
    MutSx (MSH2, MSH6)
  2. Mistake excision
    MutLx (MLH1/PMS2)
    exonuclease (EXO1)
  3. Mistake repair
    Pol gamma
    PCNA
    RPA
    DNA ligase

DNA repair I - Floyd

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15
Q

What are the key molecules involved in these parts of nucleotide excision repair?

  1. Mistake recognition
  2. Mistake excision
  3. Mistake repair
A
  1. Mistake recognition
    RNA polymerase I and II
    CSA and CSB
  2. Mistake excision
    TFIIH
    XPD, XPG, XPF-ERCC1
    5’nuclease
    RPA
  3. Mistake repair
    PCNA
    Poly gamma/epsilon/kappa
    DNA ligase I or III
    XRCC1

DNA repair I - Floyd

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16
Q

What are the key molecules involved in these parts of base excision repair?

  1. Mistake recognition
  2. Mistake excision
  3. Mistake repair
A
  1. Mistake recognition
    DNA glycosylase (MYH)
    AP lyase
  2. Mistake excision
    APE 1
    AP lyase
    PARP1
    XRCC1
    Fen1
    PCNA
    PolyB
    Pol gamma/epsilon
  3. Mistake repair
    XRCC1
    PolB
    Fen1
    DNA ligase I
    DNA ligase III

DNA repair I - Floyd

17
Q

Which genetic diseases are associated with defects in base excision repair?

A

Often embryologically lethal
POLB mutations found in 30% of human cancers
MYH mutations increase susceptibility to colon cancer

DNA repair I - Floyd

18
Q

Which genetic diseases are associated with defects in nucleotide excision repair?

A

Xeroderma pigmentosum (XP gene mutations)

DNA repair I - Floyd

19
Q

Which genetic diseases are associated with defects in mismatch repair?

A

Lynch syndrome (hereditary nonpolyposis colorectal cancer) (MSH2 and MLH1)

DNA repair I - Floyd

20
Q

Which genetic diseases are associated with defects in homologous recombination?

A

BRCA1/2 mutations
Fanconi anemia (FANC genes)
ataxia-telangiectasia (ATM)

DNA repair I - Floyd

21
Q

Which genetic diseases are associated with defects in non-homologous end joining?

A

LIG4 syndrome (LIG4)
XLF-SCID (XLF)

22
Q

Name two assays to measure cell proliferation.

A

Tritiated Thymidine (3H-TdR) and Bromodeoxyuridine (BrdU) Assays

These nucleoside analogues incorporate into DNA in proliferating cell populations
Higher levels = higher proliferation

Cell cycle

23
Q

Which lab method is used for synchronization of the cell population?

A

mitotic shakeoff - enriches for mitotic cells
Thymidine block (or double thymidine block) - blocks cells at G1/S

Cell cycle

24
Q

Which part of the cell cycle is the most variable (most regulated)?

A

G1

Cell cycle

25
Q

Which part of the cell cycle, stem cells are in mostly?

A

G0

Cell cycle

26
Q

What does cell cycle analysis do?

A

Stain DNA with propidium iodide
flow -> quantify fluorescent signal
allows discremination between N (pre-S) and 2N (post-S)
know the graph

Cell cycle

27
Q

What is the difference between G0 of normal and cancer cells?

A

Cancer cells usually don’t enter G0 unless something happens

Normal cells - physiologically enter GO as a normal process
* Tumor cells - most often don’t enter GO unless some stimulus induces it (low growth factors, cell-cell contact inhibition)

Cell cycle

28
Q

Phospho-histone H3 and Ki67 stains are higher in which parts of the cell cycle?

A

Phospho-Histone H3 - high in S phase
Ki67 - high in G2/M phase

Roughly correlate to the number of cells proliferating

Cell cycle

29
Q

Which cyclins are most active in which parts of the cell cycle?

A

DEAB
D: G1
E:S
A:G2
B:M

Cell cycle

30
Q

Which cyclin/CDKs are associated with which parts of the cell cycle?

A

D/CDK 4/6: G1 till R point
E/CDK 2: R point - early S
A/CDK2 - early S
A/CDC2 - S/G2
B/CDC2 - M

Cell cycle

31
Q

What does pimonidazole do?

A

Detects hypoxia

Hypoxia

32
Q
A

Radiation Biology (4 decks)

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