Lecture 11 DNA effects

Question 1

Nitrogenous bases

Answer 1

adenine+thymine, guanine+cytosine

Question 2

DNA

Answer 2

Desoxyribo Nucleic Acid

Question 3

What shows that the nucleus is more sensitive than cytoplasm

Answer 3

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.

Question 4

What bases can sensitize the DNA cells

Answer 4

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

Question 5

3H

Answer 5

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

Question 6

Sensitizer

Answer 6

a drug that blocks DNA repair

Question 7

Radiosensitive cells

Answer 7

that have a low number of repair enzymes

Question 8

DNA width

Answer 8

20A or 2 nm. Double strand helix

Question 9

Most common form of naturally occurring DNA damage

Answer 9

Apurinic/apyrimidinic sites up to 20000 per day

Question 10

Each time cell divides how many DSb and SS it forms

Answer 10

10 and 50 000 accordingly

Question 11

misrepair of DNA

Answer 11

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

Question 12

DNA repair pathways

Answer 12

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

Question 13

describe base excision repair

Answer 13

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

Question 14

describe nucleotide excision repair

Answer 14

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.

Question 15

non-homologous end-joining (NHEJ)

Answer 15

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

Question 16

homologous end-joining (NHEJ)

Answer 16

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.

Question 17

mismatch mechanism

Answer 17

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

Question 18

crosslink repair

Answer 18

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

Question 19

chromatin

Answer 19

beds on a string of DNA

Question 20

chromosome consists of

Answer 20

chromatin fibers sections 1400 nm width

Question 21

Complementary DNA strands are

Answer 21

hybridized via H-bonding and unwind under alkaline conditions.

Question 22

The yield of rad damage is affected

Answer 22

by the macromolecular organization of DNA

Question 23

Popular DNA damage assays

Answer 23

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.

Question 24

Research DNA damage assays

Answer 24

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

Question 25

Neutral and Alkaline Elution Assays

Answer 25

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

Question 26

pH of neutral elution

Answer 26

7.4

Question 27

pH of alkaline elution

Answer 27

12.2

Question 28

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

Answer 28

as # of breaks increase

Question 29

Comet assay is useful because

Answer 29

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

Question 30

Pulse-Field Gel Electrophoresis (PFGE)

Answer 30

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.

Question 31

gamma 2AX

Answer 31

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

Question 32

cell division stages

Answer 32

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

Question 33

Cytogenetic damage assessed

Answer 33

at first metaphase after irradiation

Question 34

early irradiation and both sister chromatids involved

Answer 34

Chromosome aberration

Question 35

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

Answer 35

chromatid aberration

Question 36

Lesion types

Answer 36

deletion type and exchange type

Question 37

Exchange type rearrangement

Answer 37

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

Question 38

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

Answer 38

to deletion and ring

Question 39

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

Answer 39

to dicentric and deletion

Question 40

cell division

Answer 40

mitosis

Question 41

Chromosome analyses

Answer 41

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

Question 42

Micronucleus assay

Answer 42

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

Question 43

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

Answer 43

Y= proportionality*Dose, used for deleton.

Question 44

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

Answer 44

Y= proportionality*Dose + beta*Dose^2, used for lethal

Question 45

Ionizing Radiation induces

Answer 45

base damage, SSBs, DSBs, and DNA | protein crosslinks

Question 46

DNA DSB

Answer 46

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

Question 47

Defective nonhomologous recombination

Answer 47

leads to chromosome | aberrations and ionizing radiation sensitivity

Question 48

Radiation-induced breakage and incorrect rejoining in | prereplication (early) chromosomes

Answer 48

may lead to chromosome aberrations

Question 49

Radiation-induced breakage and incorrect rejoining in | postreplication (late) chromosomes

Answer 49

may lead to chromatid aberrations

Question 50

0.25 Gy

Answer 50

The lowest single dose that can be detected readily

Question 51

stable aberrations persist for many years

Answer 51

true

Question 52

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

Answer 52

true