MOLECULAR & CELLULAR RADIOBIOLOGY, EARLY EFFECTS OF RADIATION Flashcards
What are point lesions in molecular radiobiology?
Cellular radiation damage that leads to late radiation effects.
What are the two processes metabolism consists of?
Catabolism and anabolism
Which molecule is considered the most radiosensitive?
DNA.
What is the principal radiation interaction in the human body?
Radiation interaction with water.
Irradiation outside of the cell or body.
in vitro irradiation
Irradiation within the cell or body.
in vivo irradiation
The breakage of the backbone of long-chain macromolecules.
main-chain scission
What does main-chain scission result in?
Reduction of a long molecule into many smaller ones and decreased viscosity.
What effect does cross-linking have on macromolecules?
Increases the viscosity of the solution.
A change that impairs or loses function at a single chemical bond.
point lesion
The reduction of nutrient molecules for energy.
catabolism
The production of large molecules for form and function.
anabolism
What is translation in protein synthesis?
Forming a protein molecule from messenger RNA.
What is transcription?
Constructing messenger RNA from DNA.
Which is more abundant, proteins or nucleic acids?
Proteins.
Which is less radiosensitive, proteins or nucleic acids?
Proteins.
Deoxyribose, phosphate, and base molecules accumulate, forming the double-helix DNA.
G1 portion of interphase
DNA unzips and forms two daughter DNA molecules.
S portion of interphase
What do chromosomes control in a cell?
The growth and development of the cell.
What are the two types of chromosome aberrations?
Terminal deletion and dicentric formation.
What is an ion pair created by radiolysis of water?
HOH+ and e-.
Uncharged molecules with an unpaired electron; short-lived.
free radicals
What toxic agent is formed by radiolysis of water?
Hydrogen peroxide (H2O2).
What is the principal damaging product of radiolysis of water?
Hydroperoxyl radical (HO2*).
When the initial ionizing event occurs on the target molecule.
direct effect
When the ionizing event occurs on a noncritical molecule and energy is transferred.
indirect effect
Theory that a cell dies if its target molecule is inactivated by radiation.
target theory
What is a radiation “hit”?
An ionization that inactivates the target molecule.
How does low-LET radiation interact in the absence of oxygen?
Low probability of hitting target molecules.
How does oxygen affect low-LET radiation?
Increases probability of a hit by forming free radicals.
What model applies to enzymes, viruses, and bacteria for cell survival?
Single-Target, Single-Hit Model.
Define D37.
Dose required to kill 63% of cells (37% survive); measures cell radiosensitivity.
Which phase is most variable in cell cycle time?
G1 phase.
Which cell survival model applies to human cells?
Multi-Target, Single-Hit Model.
What does a high D0 value indicate?
Radioresistant cells.
What does DQ represent in the multitarget model?
The threshold dose and cell recovery capacity.
Damage that must accumulate before cell death occurs.
sublethal damage
Describes the cell’s ability to recover from sublethal damage.
split-dose irradiation
What is the average cell-cycle time for human cells?
Approximately 24 hours.
Which phase in the cell cycle is the most sensitive to radiation?
Mitosis.
How does oxygen influence radiation effects?
Enhances the effect of low-LET radiation.
What type of radiation response is deterministic?
A response that varies in severity with radiation dose and has a threshold.
What is the prodromal period in acute radiation syndrome?
Initial symptoms like nausea and vomiting after exposure.
What characterizes the hematologic syndrome?
Reduction in white, red cells, and platelets; dose range 200-1000 rad.
What dose range causes GI syndrome?
1000-5000 rad.
What symptoms are associated with CNS syndrome?
Ataxia, seizures, and loss of coordination.
What does LD50/60 measure?
Dose causing 50% of subjects to die within 60 days.
What tissues are most affected by local radiation exposure?
Skin, gonads, and bone marrow.
Shrinkage of an organ or tissue due to cell death.
atrophy
What are the three layers of skin?
Epidermis, dermis, and subcutaneous layer.
What cells in the skin are most radiosensitive?
Basal cells in the epidermis.
Reddening of the skin similar to sunburn.
erythema
Ulceration and peeling of the skin.
desquamation
What dose causes temporary epilation?
300 rad.
What is the SED50?
Dose causing skin erythema in 50% of people, about 500 rad.
What dose causes temporary sterility in men?
200 rad.
What dose causes permanent sterility in women?
500 rad.
Includes bone marrow, circulating blood, and lymphoid tissue.
hemopoietic system
What cells are involved in the immune response?
Lymphocytes.
rapid decrease in granulocytes.
granulocytopenia
Platelets involved in blood clotting.
thrombocytes
What cells are least sensitive to radiation?
Erythrocytes (red blood cells).
A chromosome map used in cytogenetic analysis.
karyotype
What are single-hit chromosome aberrations?
Chromosomal damage observed during the M phase.
A chromosome formed by joining segments from two hits.
dicentric chromosome
The study of cell genetics, particularly chromosomes.
cytogenetics
How are radiation-induced point mutations detected?
They are undetectable even with karyotype analysis.
What is the dose-response relationship for single-hit aberrations?
Linear, nonthreshold.
What are iso-chromatid fragments?
chromatid fragments without centromeres.
What causes stickiness in chromosomes?
Mechanism failure for chromatid joining.
What radiation dose affects lymphocytes?
As little as 25 rad can cause hematologic depression.
A rapid rise in granulocytes, typically after exposure.
granulocytosis
What is the principal effect of radiation on blood cells?
Depression of blood cell numbers.
Red blood cells that transport oxygen
erythrocytes
How long do red blood cells live in the peripheral blood?
Approximately 4 months.
What is the most radiosensitive phase of male gametogenesis?
Spermatogonial stem cells.
What causes radiation-induced atrophy of the ovaries?
Irradiation, especially early in life.
The development process of germ cells in testes and ovaries.
gametogenesis
What type of radiation is associated with orthovoltage x-rays?
200-300 kVp x-rays.
Ulceration of the skin that represents clinical intolerance.
moist desquamation
What are the symptoms of prodromal radiation sickness?
Nausea, vomiting, and diarrhea.
What is a ring chromosome aberration?
Chromosomal damage from two hits on the same chromosome.
How long is the latent period in radiation sickness?
It varies based on dose, usually no symptoms present.
What is the GI syndrome dose range?
1000-5000 rad.
Define hemopoietic cell survival.
Decrease in circulating blood cells due to radiation.
What is the approximate chromosome aberration frequency?
Two single-hit aberrations per rad per 1000 cells.
What is the CNS syndrome’s ultimate cause?
Elevated fluid content in the brain.
What is the effect of high-LET radiation on cell survival models?
Follows single-target, single-hit model.
What is a reciprocal translocation?
A rearrangement of genes without genetic loss.
What cells recover from radiation damage in 6 months to 1 year?
Erythrocytes.
What is a lethal dose response?
Nonlinear, threshold for acute radiation lethality.
What does radiation-induced thrombocytopenia cause?
Depletion of platelets, leading to hemorrhage risk.
What is the primary function of lymphocytes?
Immune response regulation.
What radiation dose can suppress menstruation in women?
As little as 10 rad.
What cell system is similar to hemopoietic system?
Gametogenesis, both involve cell renewal.
What is a bone marrow’s function in adults?
Produces most circulating blood cells.
What type of radiation effect follows a threshold relationship?
Deterministic effects like local tissue damage.
What are the three main effects of radiolysis?
Ion pair formation, free radicals, and hydrogen peroxide.
What is the dose threshold for chromosome aberrations?
Approximately 5 rad.
What is the lifespan of granulocytes in bone marrow?
8-10 days.
What dose causes erythema in radiation patients?
Approximately 200 rad.
What cells show a nonthreshold response to chromosome aberrations?
Human lymphocytes.
What are the symptoms of CNS radiation syndrome?
Disorientation, seizures, loss of muscle coordination.
What does linear energy transfer determine?
The magnitude of biological damage.
What does RBE compare?
Effectiveness of test radiation vs. x-radiation.
