Lesson 8:Radiation Effects on DNA, Chromosomes and Cells

Question 1

On what 3 levels is radiation damage observed

Answer 1

• molecular (DNA/RNA)
• cellular (cell structure)
• organic

Question 2

When does visible radiation injuries behin

Answer 2

with damage at the molecular level

Question 3

What does molecular damage result in

Answer 3

structurally changed molecules that impair cell functioning

Question 4

What is a chromosome

Answer 4

tiny rod shaped bodies that are composed of protein and DNA
- normal cells have 46 chromosomes
- reproductive cells have 23

Question 5

DNA Genes Chromosomes Filing cabinet reference

Answer 5

DNA - paper
Genes - File folder
Chromosome - Filing cabinet

Question 6

4 categories if radiation effects on DNA

Answer 6

• Base damage
• single strand breaks
• double strand breaks
• crosslinks or crosslinking

Question 7

What is base damage

Answer 7

• change/loss of a base
• mutation

Question 8

What is a single strand break

Answer 8

• break in the backbone of one chain of a DNA molecule
• ionizing radiation interacts with DNA molecule
• transfers energy and ruptures one of the bonds (sugar phosphate chains)
• repair enzymes often capable of repairing this damage

Question 9

What is double strand break

Answer 9

Break in both chains of a DNA molecule
- breaks on the same side can be repaired but not as easily
- breaks on either side result in a broken chromosome containing an unequal amount of genetic material
- if damaged chromosome divides each new cell will experience cell death or impaired functioning

Question 10

What is crosslinking

Answer 10

• Within the DNA molecule (instrand)
• from one molecule to another (interstrand)

Question 11

What is DNA mutation & 4 possible outcomes for DNA mutation

Answer 11

• molecular change that is not visible in the chromosome
• cell repair
• metabolic changes causing malignancies
• genetic damage to reproductive cells
• cell death / organ and tissue damage

Question 12

Effects of Crosslinking

Answer 12

• direct action by high LET
• indirect by low LET
• some molecules fragment and change into sticky molecules that stick to themselves or other molecules
• can cause reproduction arrest or cell death

Question 13

What is intrastrand crosslinks

Answer 13

between 2 regions of the same DNA strand

Question 14

what is interstrand cross links

Answer 14

between 2 complimentary strands or completly differeny molecules

Question 15

Effects of mutation

Answer 15

causes either a loss of or change in a nitrogenous
base on the DNA chain.
* Direct consequence is an alteration of the
base sequence, a mutation.
* May not be reversible and may cause acute
consequences for the cell
* If cell remains viable, incorrect genetic
information will be transferred to one of the
two daughter cells when the cell divides.

Question 16

Effects of ionizing radiation on chromosomes

Answer 16

Radiation-induced chromosome breaks in both somatic and
reproductive cells
* Chromosomal fragments
* Chromosome anomalies
* Chromosome aberrations
* Chromatid aberrations
* Structural changes in biologic tissue caused by ionizing radiation

Question 17

Chromosome vs Chromatid Aberration

Answer 17

1) Chromosome Abberations damage from radiation occurs before S-phase
2) Chromatid Abberations: damage from radiation occurs after S -phase
- only one daughter cell affected

Question 18

When are cells most and least sensitive during reproductive cycle

Answer 18

• cells are always most sensitive in reproductive cycle
• cells are more radioresistant during late S phase

Question 19

Structural changes caused by radiation

Answer 19

• Single break in one chromosome or chromatid
• Single break in separate chromosomes or chromatids
• Two or more breaks in the same chromosome or chromatid

Question 20

What is restitution

Answer 20

• Consequences to the Cell from Structural Changes in Biologic Tissue
• Breaks rejoin, no visible damage
• No injury to the cell
• 95% mending/healing

Question 21

What is deletion

Answer 21

Consequences to the Cell from Structural Changes in Biologic Tissue
* Fragments lost during mitosis
* After DNA synthesis only part of the chromosome has been replicated
* left with an acentric fragment (no centromere)

Question 22

Broken end rearrangement/distorted chromosomes

Answer 22

rearrangement of broken ends
Consequences to the Cell from Structural Changes in Biologic Tissue

Question 23

2 breaks in a single chromatid

Answer 23

• leaves a ring chromatid and acentric fragment
  Consequences to the Cell from Structural Changes in Biologic Tissue

Question 24

breaks in 2 different chromatids

Answer 24

fragments are seperated
Consequences to the Cell from Structural Changes in Biologic Tissue

Question 25

Broken end rearrangement or distorted chromosomes

Answer 25

rearrangment of broken ends Consequences to the Cell from Structural Changes in Biologic Tissue

Question 26

ends of chromatids and ends of Fragments join prior to DNA synthesis

Answer 26

Consequences to the Cell from Structural Changes in Biologic Tissue * Ends of Chromatids and ends of Fragments join prior to DNA synthesis (F, G) * forming dicentric and acentric fragments * Chromosome is elongated but cannot split * Centromeres are ‘bridged’ * Reproductive death of the cell

Question 27

Broken end rearrangement without visible damage to the chromatids (translocations)

Answer 27

Consequences to the Cell from Structural Changes in Biologic Tissue translocation - genetic material has been rearranged - drastic change to cell function - cell death or failure to replicate properly

Question 28

Broken end rearrangement without visible damage to the chromatids (inversions)

Answer 28

Consequences to the Cell from Structural Changes in Biologic Tissue Inversions - Genetic material has been rearranged * Drastic change to cell function * Cell death or failure to replicate properly

Question 29

Damage to the cell nucleus possibilities

Answer 29

- instant death - high doses, DNA breaks up - reproductive death - survives but cant replicate - apoptosis - or programmed cell death (interphase death) - mitotic or genetic death - dies trying to divide - mitotic delay - division delay - interference with function - chromosome breakage

Question 30

What happens when too many somatic cells are affected by radiation

Answer 30

entire body processes may be disrupted

Question 31

what happens if radiation damages the germ cells

Answer 31

damage may be passed to future generations in the form of genetic mutations (mostly recessive)

Question 32

What is dose response relationships

Answer 32

a mathematical relationship between various radiation dose levels and the magnitude of the observed response - High levels of x-rays can cause skin burns, cataracts, cancer, leukemia and other harmful effects - Unknown is the degree of effect after exposure to diagnostic or therapeutic levels of radiation

Question 33

What 2 characteristics does every radiation dose response have

Answer 33

1. linear or non linear 2. threshold or non threshold - diagnnostic radiology is linear non threshold - no exposure is without risk but small doses have very low risk