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Chapter 6 sherer

Molecular & Cellular Radiation Biology

What is Radiation Boilogy? The branch of biology concerned with the effects of ionizing radiation on liveing systems.
How do x-rays and gamma-rays transfer energy? impart energy to orbital electrons in atoms if the photons happen to pass near the electrons.
How do high engery particles like alpha and beta particles transfer energy? By interacting electromagnetically with orbital electrons.
What factors vary among different types of radiation? Charge, mass, and energy
What are the three important concepts that must be studied to understand the injuries caused from ionizing radiation? Linear energy transfer (LET), radiation biological effectiveness (RBE), and oxygen enhancement ratio (OER)
What is LET linear energy transfer? The average energy deposited per unit length of track (path of energy deposited from ionizing radiation)The amount of destruction to tissue depending on the energy of radiation.
What is the LET for diagnostic purposes? 3 keV/mm (kiolelectron volts per micron [10`6])
What types of radiation are considered to be low-LET? x-rays, gamma rays, beta rays
What types of radiation are considered to by high-LET? Alpha particles, Ions of heavy nuclei, charged particles released from ineractions between neutrons and atoms, and low-energy neutrons
Whet LET increases what happens to the likelihood of producing a biologic response? The likelihood of producing a biological response as a result of more frequent occurrence of ionizations also increases.
Which is more likely to be affected by OER? low or high LET? Low because when low-LET radatio interacts w/tissue it causes damage through INDIRECT action that involves the production of free radicals which behave as extremely reactive entities.
What must a particle include to be considered a high-LET? They must posses substantial mass and charge
Which types of LET loses energy at a quicker pace-low or high? High because they produce much more ionziation per unit of distance traveled and as a result, they exhaust their energy in a shorter length of track and therefore cannot travel or penetrate as far.
What happens each time a high LET particle reacts? It loses some energy and eventually will slow down enough to stop so that no other reactions will occur.
Which travels farther an electron or alpha particle? Electron
Wht is internal contamination? When a radionuclide has been implanted, injested, inhaled, or injected
What is relative biological effectiveness (RBE)? A ratio that describes the relative capabilities of radiation with differing LETs to produce a particular biologic reaction.
What is the oxygen Enhancement ratio? The ratio of the radiation dose required to cause a particular biologic response of cells or organisms in an oxygen-deprived environment to the radiation dose requred to cause an identical response under normal oxygenated conditions
What is the OER for x-rays? about 3 for x-rays and gamma rays
What is the OER for alpha particles? equal to 1
What is the Wr (radation weighting factor) for alpha particles? 20
With oxygen present damage from radiation ________ be fixed but without oxygen damage from radiation ______be fixed. CANNOT......CAN
What three levels can biologic damage resulting from exposure to ionizing radation be observed? Molecular, cellular, and organic
How does direct action occur within a cell? Occurs as a result of ionziation of atoms on master, or key molecules (DNA), which can cause these molecules to vecome inactive or functionally altered.
How does indirect action occur within a cell? When a free radical (a product of radiation reaction w/water molecules) interacts with another cell it can alter its function and lead to cell death. The new interactions hydrogen peroxide, hydroxyl will initiate harmful reactions to the cell.
What is a single strand break? The energy transferred fr: radiation interacting can rupture one of DNA's chemical bonds, possibly a sugar-phosphate chain side rails which is called a POINT MUTATION
What type of LET do point breaks occur? Low-LET
What is a Double Strand Break? Further exposure to radiation may result in additional breaks in sugarphosphate chains. Breaks can be repaired but if breaks go unrepaired, further separation may occur in DNA chains, threatening life of cell.
What is radiolosis of water? Interaction of radiation and water. Creates an ion pair consisting of a water
What are the possiblities during radiolosis? 1. fractured H2O mole. can reunite & form a stable water mole. 2. fractured H2O mole. can break up further creating free radicals 3. A hydroxyl radical (OH*) may bond w/ another hydroxyl radical (OH*) & form hydrogen peroxide (H2O2)mole. HOH+ plus an e-
Is a duoble stranded DNA break most likely caused by low or high LET? High LET
What is a double-strand break on the same rung? Same rung of DNA is hit (two interactions occur)with a result of a cleaved or broken chromosome with each new portion containg an unequal amt of genetic material.
What is a mutation? the loss or change of DNA chain; may or may not be reversible and may cause acute consequences for the cell but, more important, if the cell remains viable, incorrect genetic info will be transferred to 1 or the 2 daugher cells when cell divides
After chromosome breakage, how many fragments are produced? Two or more and each ends appear sticky and have the ability to adhere to another such sticky end. They may rejoin original configuration, fail to rejoin & create an aberration, or rejoin other broken ends & create new chromosomes
What are the 2 types of chromosome anomalies observed in metaphase? chromosome aberrations and chromatid aberrations
which of the anomalies happens in late interphase, after DNAsynthesis has taken place? chromatid aberrations
Which of the anomalies happens in early interphase, before DNA synthesis takes place? chromosome aberrations
What are the structural changes that occur from irradiation? Restitution, Deletion, Broken-end rearrangment, & Broken-end rearrangement w/out visible damage
What is restitution? After ionizing radiation has caused DNA damag the breaks will rejoin in their original configuration with no visible damage.
What is Deletion? After irradiation to the cell, part of the chromosome or chromatid is lost at the next cell division, creating an aberration known as an acentric fragment.
What is a Broken-end rearrangement? Whereby a grosslyt misshapen chromosome nay be produced.
What is a Broken-end rearrangement w/o visible damage? Whereby the chromatids's denetic material has been rearranged even though the chromatid appears normal.
What is the target theory? States a cell will die after exposure to ioning radition ONLY if the master, or key, molecule (DNA) is inactivated in the process.
What are the 7 ways a cell can be affected by ionizing radiation? 1) Instant death 2) Repoductive death 3) Apoptosis/ programmed cell death 4) Mitotic death 5) mitotic delay 6) inerference w/function 7) chromosome breakage
What is the dose required for instant death to occur to a cell? 1000 Gy (100,000 rad)
What is the dose required for reproductive death to occur to a cell? 1-10 Gy (100-1000 rad)
What is the dose required for mitotic delay to occur to a cell? 0.01 GY (1 rad)
What does a survival curve illustrate? A classic method of displaying the sensitivity of a particular type of cell to radiation. Shows low-LET compared to high-LET.
What is another meaning for immature cells? undifferentiated
What is another meaning for mature cells? highly defferentiated
What are basal cells of the skin- radioinsinsitive or radiosensitive? radiosensitive
What are lymphocytes- radioinsinsitive or radiosensitive? radiosensitive
What are erythrocytes- radioinsinsitive or radiosensitive? radiosensitive
What are intestinal crypt cells- radioinsinsitive or radiosensitive? radiosensitive
What are reproductive cells- radioinsinsitive or radiosensitive? radiosensitive
What are brain cells- radioinsensitve or radiosensitive? radioinsensitve
What are nerve cells - radioinsinsitive or radiosensitive? radioinsinsitive
What are muscle cells - radioinsinsitive or radiosensitive? radioinsinsitive
What does the Law of Bergonie and Tribondeau state? That the radiosensitivity of cells is directly proportional to their reproductive activity and inversely proportional to their degree of differentiation. The most pronounced radiation effects occur in cells having the least maturity or specialization.
How much radiation does it take to produce a measurable hematologic depression? .25 Gy (25rad)
What is LD and what does 50/30 & 50/60 stand for? Lethal Dose. The amount it takes to kill 50% of the population in 30 (animals) or 60 (humans) days. (humans take longer to recover than animals)
What is the Lethal Dose (LD) for humans? 3.0-4.0 Gy (300-400 rad)
What is the most radiosensitive blood cell in the body? Lymphocytes
What is the range of WBCs in an adult? 5000-10,000/mm3 of blood
What happens to the blood when a dose of 1 Gy or higher is recieved? The lymphocytes present in circulating blood count decreases to zero w/in a few days.
What does neutrophils do in the body and What is the lowest dose it takes to depress the number of NEUTROPHILS cells? FIght off infection/0.5 Gy (50 rad)
What does a lymphocyte do in the body and What is the lowest dose it takes to depress the number of cells? They are important in defending the body against foreign antigen by producing antibodies/ 0.25 Gy (25 rad)
What are granulocytes and what do they do in the body? A scavenger type of WBCs that fight bacteria and only remain in the bld a few days. They INCREASE in number when radiated.
Created by: clbrock0620