Lesson 8:Radiation Effects on DNA, Chromosomes and Cells Flashcards
On what 3 levels is radiation damage observed
- molecular (DNA/RNA)
- cellular (cell structure)
- organic
When does visible radiation injuries behin
with damage at the molecular level
What does molecular damage result in
structurally changed molecules that impair cell functioning
What is a chromosome
tiny rod shaped bodies that are composed of protein and DNA
- normal cells have 46 chromosomes
- reproductive cells have 23
DNA Genes Chromosomes Filing cabinet reference
DNA - paper
Genes - File folder
Chromosome - Filing cabinet
4 categories if radiation effects on DNA
- Base damage
- single strand breaks
- double strand breaks
- crosslinks or crosslinking
What is base damage
- change/loss of a base
- mutation
What is a single strand break
- 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
What is double strand break
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
What is crosslinking
- Within the DNA molecule (instrand)
- from one molecule to another (interstrand)
What is DNA mutation & 4 possible outcomes for DNA mutation
- 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
Effects of Crosslinking
- 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
What is intrastrand crosslinks
between 2 regions of the same DNA strand
what is interstrand cross links
between 2 complimentary strands or completly differeny molecules
Effects of mutation
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.
Effects of ionizing radiation on chromosomes
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
Chromosome vs Chromatid Aberration
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
When are cells most and least sensitive during reproductive cycle
- cells are always most sensitive in reproductive cycle
- cells are more radioresistant during late S phase
Structural changes caused by radiation
- Single break in one chromosome or chromatid
- Single break in separate chromosomes or chromatids
- Two or more breaks in the same chromosome or chromatid
What is restitution
- Consequences to the Cell from Structural Changes in Biologic Tissue
- Breaks rejoin, no visible damage
- No injury to the cell
- 95% mending/healing
What is deletion
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)
Broken end rearrangement/distorted chromosomes
rearrangement of broken ends
Consequences to the Cell from Structural Changes in Biologic Tissue
2 breaks in a single chromatid
- leaves a ring chromatid and acentric fragment
Consequences to the Cell from Structural Changes in Biologic Tissue
breaks in 2 different chromatids
fragments are seperated
Consequences to the Cell from Structural Changes in Biologic Tissue
Broken end rearrangement or distorted chromosomes
rearrangment of broken ends
Consequences to the Cell from Structural Changes in Biologic Tissue
ends of chromatids and ends of Fragments join prior to DNA synthesis
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
Broken end rearrangement without visible damage to the chromatids (translocations)
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
Broken end rearrangement without visible damage to the chromatids (inversions)
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
Damage to the cell nucleus possibilities
- 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
What happens when too many somatic cells are affected by radiation
entire body processes may be disrupted
what happens if radiation damages the germ cells
damage may be passed to future generations in the form of genetic mutations (mostly recessive)
What is dose response relationships
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
What 2 characteristics does every radiation dose response have
- linear or non linear
- threshold or non threshold
- diagnnostic radiology is linear non threshold
- no exposure is without risk but small doses have very low risk
