30 Questions
Which type of cell division results in two genetically identical daughter cells?
Mitosis
What is the defining feature of the S portion of the cell cycle?
DNA synthesis
During which phase of the cell cycle is DNA synthesized but other metabolic processes are taking place?
G2 phase
Which period of the cell cycle is not characterized by DNA synthesis?
M phase
During which phases of the cell cycle are cells most radio-sensitive?
M and G2 phases
What characterizes the cell cycle time for stem cells in certain tissues?
Up to 10 days
Which of the following is true about the adaptive response to radiation?
It results in a lower than expected number of chromosomal aberrations following a second dose.
How does oxygen tension affect cell sensitivity to low LET radiation?
Cells with normal concentrations of oxygen tend to be 2-3 times as sensitive to low LET radiation as hypoxic cells.
What is the purpose of radioprotective drugs?
To reduce the effective dose of radiation when injected prior to an acute exposure
What are chemical agents that reduce cell response to radiation called?
Radioprotectors
Why do females tend to be slightly more radioresistant than males?
Variability in female hormonal levels reduces lymphocyte radiosensitivity.
According to age, which group is the most radio-sensitive?
Fetus
What is the most important site of damage in a cell due to radiation?
DNA
Which type of radiation usually causes isolated DNA damage?
Low LET radiation
What is more complex and harder to repair than isolated damage?
Double strand breaks
What type of DNA damage is typically repaired using base-excision repair mechanisms?
Base damage
What are the possible outcomes of cell irradiation mentioned in the text?
Division delay, reproductive failure, cancer, genomic instability
What type of effects are suffered by individuals during their lifetime due to radiation?
Somatic effects
Which type of effects from radiation exposure have a probability of occurrence that increases with dose but no relation to severity?
Stochastic effects
What type of radiation-induced effects are highly predictable, with a threshold dose that triggers a dose-dependent response?
Deterministic effects
What is represented by the shoulder on the cell survival curve?
DNA repair mechanism
Which type of radiation can result in more complex DNA damage, making repair more difficult?
High LET radiation
When is cell death most sensitive to radiation?
During the mitotic phase and late G1
What may low doses of radiation initiate that reduces the consequences of subsequent exposures?
Adaptive responses
Which type of radiation can be shielded with Plexiglas?
Beta particles
What is the term used to describe the amount of energy imparted locally in a target by radiation?
Linear Energy Transfer (LET)
Which radiation type has the highest ability to penetrate materials?
Gamma rays
Which effect of radiation involves a transfer of energy from the radiation directly to the target molecule, typically DNA?
Direct radiation effects
What can lead to tissue damage, with an estimated two-thirds of the biological damage caused by low LET radiation being due to indirect action?
Reactive oxygen species (ROS)
What is believed to be particularly important in producing biological damage by the indirect action of x-rays?
Hydroxyl radicals
Study Notes
- Cell death for stem cells and other cells with high division capacity is referred to as reproductive death.
- Apoptosis is a process by which an organism induces cells that may pose a threat to commit suicide.
- Apoptosis can be induced by radiation, which is generally a good thing since dead cells don't become cancerous.
- Failure of apoptosis can increase the probability of malfunctioning cancerous cells proliferating if radiation damages the genes that induce apoptosis.
- Radiation is classified into two main categories: non-ionizing and ionizing.
- Ionizing radiation can be further divided into directly ionizing (charged particles) and indirectly ionizing (neutral particles) radiation.
- Ionizing radiation has the ability to penetrate and transfer energy to the material it is penetrating. The term "Linear Energy Transfer" (LET) is used to describe the amount of energy imparted locally in a target.
- Alpha particles have a high LET, low penetrating ability, and can be shielded by a piece of paper.
- Beta particles have a low LET and can only penetrate low-density materials, they can be shielded with Plexiglas.
- X-rays and gamma rays have a low LET and the highest ability to penetrate materials. High-density materials are needed to shield against these waves.
- X-rays interact with atoms through the photoelectric effect, Compton scattering, or pair production, resulting in the production of free radicals that can damage DNA.
- Direct radiation effects involve a transfer of energy from the radiation directly to the target molecule, typically DNA. These effects are most important for high LET radiation.
- Indirect radiation effects occur when radiation produces free radicals that react with the target molecule, typically DNA. These effects are most important for low LET radiation.
- Indirect radiation effects can be modified by chemical sensitizers or radiation protectors.
- Ionizing radiation interacts with water, leading to the production of free radicals that can damage DNA and other molecules.
- The presence of an excess of oxygen during irradiation of cells allows the formation of additional free radicals.
- Much of the damage caused by radiation is believed to be due to oxygen containing radicals, ions, and peroxides collectively known as reactive oxygen species (ROS).
- The hydroxyl radicals are believed to be particularly important in producing biological damage by the indirect action of x rays.
- Radiation leads to tissue damage, with an estimated two-thirds of the biological damage caused by low LET radiation being due to indirect action.
- Radiation-induced malignancies can occur if the radiation directly affects somatic cells and alters the DNA (and hence the chromosomes) as a result.
Test your knowledge of radiation-induced damage to subcellular targets such as DNA and membranes. Explore the effects of radiation on reproductive stem cells and the potential for congenital abnormalities.
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