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262 > Lecture 11 DNA effects > Flashcards

Lecture 11 DNA effects Flashcards

1
Q

Nitrogenous bases

A

adenine+thymine, guanine+cytosine

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2
Q

DNA

A

Desoxyribo Nucleic Acid

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3
Q

What shows that the nucleus is more sensitive than cytoplasm

A

selective irradiation showed that the nucleus has a 100 times smaller killer dose than the cytoplasm. Radioisotopes incorporated into DNA kill cells more efficiently than in RNA or in proteins. 125I is 300 more effective in DNA than in cytoplasm or membrane.

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4
Q

What bases can sensitize the DNA cells

A

Iodine or bromine- halogenated bases and any incorporations make the DNA more susceptible to damage

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5
Q

3H

A

is useful for DNA incorporation: range 3 micrometers and E beta = 18kev.

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6
Q

Sensitizer

A

a drug that blocks DNA repair

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7
Q

Radiosensitive cells

A

that have a low number of repair enzymes

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8
Q

DNA width

A

20A or 2 nm. Double strand helix

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9
Q

Most common form of naturally occurring DNA damage

A

Apurinic/apyrimidinic sites up to 20000 per day

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10
Q

Each time cell divides how many DSb and SS it forms

A

10 and 50 000 accordingly

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11
Q

misrepair of DNA

A

non-lethal error incorporated and passed on to daughter cell (can lead to genomic instability and cancerogenesis)

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12
Q

DNA repair pathways

A

SSB: Base excision (BER) and nucleotide excision repair (NER)
BSB: non-homologous end-joining (NHEJ) and homologous recombination repair (HRR)
Crosslink repair and mismatch repair

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13
Q

describe base excision repair

A

removal and replacement of modified bases; DNA glycosylase binds DNA and removes the bases that are damaged; apurinic/apyrimidinic endonuclease breaks the backbone and polymerase fills the ga, ligase seals the break

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14
Q

describe nucleotide excision repair

A

due to UV thymine has dimer; once it is detected DN creates a bubble, enzymes cut damaged part of bubble and polymerase replaces it and ligase seals.

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15
Q

non-homologous end-joining (NHEJ)

A

just joins ends of parts separated by DSB after degradation from ends. Mostly for 1 chromatid

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16
Q

homologous end-joining (NHEJ)

A

use sister chromatid to restore and recombine the damaged and lost DNA during DSB. The damage repaired accurately using info from sister chromatid.. For 2 chromatids.

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17
Q

mismatch mechanism

A

recognitions that the pair mismatch (T+G for example), them the strand is removed and resynthesized

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18
Q

crosslink repair

A

fork-> dsb->replacement of damaged region by attaching the opposite

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19
Q

chromatin

A

beds on a string of DNA

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20
Q

chromosome consists of

A

chromatin fibers sections 1400 nm width

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21
Q

Complementary DNA strands are

A

hybridized via H-bonding and unwind under alkaline conditions.

22
Q

The yield of rad damage is affected

A

by the macromolecular organization of DNA

23
Q

Popular DNA damage assays

A

for both DSB and SSB: neutral and alkaline elution through filter or separation on sucrose gradients;
Comet assay: sensitive for SSB, less for DSB;
gamma 2AX focus formation at DSB.

24
Q

Research DNA damage assays

A

DNA unwinding;
pulsed gel electrophoresis (needs high dose);
Quantification of damaged bases (for oxidative stress);
PCR

25
Q

Neutral and Alkaline Elution Assays

A

Alkaline conditions unwind DNA to measure DSB, SSB. Neutral cond measure DSB.

26
Q

pH of neutral elution

A

7.4

27
Q

pH of alkaline elution

A

12.2

28
Q

the amount of eluted DNA through the filter increases (in filter assay)

A

as # of breaks increase

29
Q

Comet assay is useful because

A

automated, can be performed on single cell, and under neutral and alkaline condition show DSB and SSB

30
Q

Pulse-Field Gel Electrophoresis (PFGE)

A

irradiate, isolate DNA, load in gel well; run a gel with pulses to force larger pieces of DNA into the gel (measure with fluorescence or radiolabel). As # of breaks increases the amount of DNA is gel also increases.

31
Q

gamma 2AX

A

add phosphorus and it will glow at the DSB within a minute with a max in 10 min. Also, repair proteins are also focused there. Dephosphorization in 30 min with t1/2 = 2. Rate of repair can be assessed in 24 h

32
Q

cell division stages

A

prophase, prometaphase, metaphase, anaphase (increased R on one side), telophase (necking), cytokinesis (divides)

33
Q

Cytogenetic damage assessed

A

at first metaphase after irradiation

34
Q

early irradiation and both sister chromatids involved

A

Chromosome aberration

35
Q

later (or in interphase) irradiation and only 1 chromatid involved

A

chromatid aberration

36
Q

Lesion types

A

deletion type and exchange type

37
Q

Exchange type rearrangement

A

chromosome break into two chromatids: translocation - ends of chromatids connect to the different (not lethal); dicentric and fragment (lethal)- ends of two chromatids connect to each other making a ring

38
Q

In chromosome and chromatid aberration inter-arm intra-change leads

A

to deletion and ring

39
Q

In chromosome and chromatid an aberration, inter-change may lead

A

to dicentric and deletion

40
Q

cell division

A

mitosis

41
Q

Chromosome analyses

A

Conventional: staining after adding a mitosis blocking agent,
Banding: staining to produce visible bands;
FISH= fluorescence in situ hybridization: uses fluorescently tagged chromosome probes to specific chromosomes or regions of chromosomes

42
Q

Micronucleus assay

A

small membrane-bound DNA fragments without centromere: - cultured cells with blocked metaphase nad stained for DNA

43
Q

Yield of radiation-induced chromosome damage formula for one target one hit

A

Y= proportionality*Dose, used for deleton.

44
Q

Yield of radiation-induced chromosome damage formula for multiple hit single target

A

Y= proportionalityDose + betaDose^2, used for lethal

45
Q

Ionizing Radiation induces

A

base damage, SSBs, DSBs, and DNA

protein crosslinks

46
Q

DNA DSB

A

most lethal form of ionizing radiation-induced damage, is repaired by nonhomologous recombination in the early phase of the cell cycle and homologous recombination in the late phase of the cell cycle

47
Q

Defective nonhomologous recombination

A

leads to chromosome

aberrations and ionizing radiation sensitivity

48
Q

Radiation-induced breakage and incorrect rejoining in

prereplication (early) chromosomes

A

may lead to chromosome aberrations

49
Q

Radiation-induced breakage and incorrect rejoining in

postreplication (late) chromosomes

A

may lead to chromatid aberrations

50
Q

0.25 Gy

A

The lowest single dose that can be detected readily

51
Q

stable aberrations persist for many years

A

true

52
Q

Scoring aberrations in lymphocytes from peripheral blood may be used to estimate total body doses in humans accidentally
irradiated.

A

true

262 (9 decks)

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