UNIT 2: Molecular & Cellular Radiation Biology Flashcards
LET(Linear Energy Transfer)
amount of energy transferred on average by incident radiation to an object per unit length of track, or passage, through the object and is expressed in units of kiloelectron volts per micrometer.
Free radicals
Solitary atoms, or most often a combination of altered atoms, that are very chemically reactive because of the presence of unpaired electrons
RBE (Relative Biological Effectiveness)
describes the comparative capabilities of radiation with differing LETs to produce a particular biologic reaction.
Anoxic
without oxygen
Hypoxic
low oxygen
OER (Oxygen Enhancement Ratio)
the radiation dose required to cause a particular biologic response of cell or organisms in any oxygen-deprived environment to the radiation dose required to cause an identical response under normal oxygen conditions
Radiolysis
the dissociation of molecules by ionizing radiation
Point lesion
when one of the sugar–phosphate chain side rails, or strands, of the ladder-like molecular structure ruptures (single-strand break)
Mutation
the loss or change of a base in the DNA chain
Erythrocyte
red blood cell without a nucleus that transport oxygen and carbon dioxide to and from the tissues.
LD 50/30
dose that produces death in 50% of the subjects within 30 days (lethal dose to animals)
LD 50/60
dose that produces death in 50% of the subjects within 60 days (lethal dose to humans)
Leukocyte
(white blood cells) protect the body from infection
Thrombocyte
(platelet) cell fragment found in large numbers in blood and involved in clotting
What areas of study are included in Radiation Biology? (3)
• The sequence of events occurring after the absorption of energy from ionizing radiation
• The action of the living system to compensate for the consequences of this energy assimilation
• Injury to the living system that may occur from irradiation
As LET increases, the chance of a significant biologic response in the radio-sensitive DNA
Increases
By which means does Low LET cause damage to biologic tissue?
- X-rays
- Gamma Rays (short wavelength, high energy waves emitted by the nuclei of radioactive substances)
Low LET is more likely to cause damage to biologic material through direct or indirect action?
Indirect
Compare and contrast how Low LET and High LET cause damage to biologic material.
-Identify the one that is more damaging to biologic tissue.
-Potential risk of damage to DNA from high LET. Low can cause damage as well but not as much damage.
-High LET can cause more damage to biologic matter than low LET.
High LET radiation penetrates more or less than Low LET radiation
Less
Low LET Radiation Examples
• Gamma Rays
• X-rays
• Electrons
High LET Radiation Examples
• Alpha Particles
• Ions of heavy nuclei
• Charged particles released from interactions between neutrons and atoms.
• Low energy neutrons
Equation for RBE
Dose in Gy from 250 kVp x-rays / Dose in Gy of test radiation
What is the purpose of RBE?
Used to describe biologic effectiveness of radiation of different quantities.
Where is RBE applied?
If the biologic effectiveness of radiation is known for x-rays, it will be used as a reference to figure out what the biological damage of a different type of radiation it will take to get the same effect as x-rays
Is RBE a useful application in radiation protection for humans?
Not really used in the diagnostic world because we use low LET, so we don’t need to test high LET for anything
Equation for OER
Radiation dose required to cause biologic response without oxygen / Radiation dose required to cause biologic response with oxygen
How does the presence of oxygen impact biologic damage with Low LET radiation
OER of 3.0 when radiation dose is high, can be 2.0 when radiation doses are below 2 Gy
How does the presence of oxygen impact biologic damage with High LET radiation
The presence or absence of oxygen is of little or no consequence to their effects. OER of about 1.0
Biologic damage from radiation can be observed on the following levels:
- Molecular
- Cellular
- Organic Systems
Ionizing radiation interactions are produced in either:
- Direct action
- Indirect action
Direct Action
Primary photon has directly hit a molecule. Occurs more often in high LET because it can produce a lot of interactions.
Indirect Action
Multistep interaction, focuses on primary photons that interact with water molecules. Chances of primary photon hitting DNA is low because our bodies are made up of 80% water and only 1% DNA. Because we have more water than DNA, almost all biological damage comes from low LET.
During direct action, how does the absorption of energy through PE and Compton interactions cause damage to the macromolecules?
The ionization, or even the excitation, of the atoms of the biologic macromolecules can result in breakage of the macromolecules’ intricate chemical bonds, causing them to become abnormal structures.
What may result if the macromolecules are damaged during these events?
Essential biochemical processes that depend on the facilitating action of the enzymes may not occur in the cell when needed. A negative biologic sequence occurs.
RADIOLYSIS OF WATER is
Radiolysis refers to the dissociation of molecules by ionizing radiation. Thus, when x-ray photons interact with water molecules contained within the human body, this can result in their separation into other molecular components.
Radiolysis of water events
- Ionization of Water Molecules
- Production of Free Radicals
- Chemical Reactions & Biologic Damage
- Cell Damaging Substances
- Organic Free Radicals
Radiolysis of water: Ionization of Water Molecules
Separation into other molecular components. Interaction creates positive water molecule and an electron
Radiolysis of water: Production of Free Radicals
-Electron goes back to a positive water molecule (no cell damage) or electron can combine with neutral water molecule and create a negative water molecule.
-Negative and positive water molecules become unstable and break apart which creates an ion pair and 2 free radicals.
Positive water molecule- end up with positive hydrogen ion and a hydroxyl radical
Negative water molecule- end up with hydroxyl ion and hydrogen radical
Radiolysis of water: Chemical Reactions & Biologic Damage
Point lesions can occur. Free radicals can travel through the cell and can destructively interact with other molecules.
Radiolysis of water: Cell Damaging Substances
The hydroperoxyl radical and hydrogen peroxide are believed to be among the primary substances that produce biologic damage
Radiolysis of water: Organic Free Radicals
Radicals RO2* and HO2* are formed. These radicals can react with other organic molecules to cause biologic damage. Thus, a small-scale chain reaction of destructive events results when radiation deposits energy within tissue in the presence of oxygen.
How does the presence/absence of oxygen impact the production of organic free radicals?
Without oxygen or a force to attract an electron, these radicals usually react with each other to reform the original organic molecule (RH). When oxygen is present, however, R* and H* may react with oxygen molecules (O2) to form the radicals RO2* and HO2*
Specifically, what causes the immediate damage in an indirect action?
The by-products of the radiation, the free radicals, are the direct cause of this damage