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Chapter 7 - Molecular & Cellular Radiation Biology

Terms in this set (174)

branch of biology concerned with the effects of ionizing radiation on living systems
radiation biology
includes: sequence of events, action of the living system, and injury to the living system
areas of study
Because we administer radiation ot humans for medical purposes, it is necessary that we have a basic understanding of cell ___, ___, and ___ as well as the adverse effects.
structure, composition, and function
Ionizing radiation damages living systems by removing ___.
electrons
What is able to interact with orbital electrons?
x-rays, gamma rays, alpha and beta particles, and protons
Biologic damage begins with the ___ produced by various types of radiation.
ionization
What are the 3 important concepts that must be studied to understand the way ionizing radiation causes injury and how the effects my vary? (abbreviations)
LET, RBE, and OER
This states that ionizing radiation may interact with a material as it passes through and deposit energy.
Linear Energy Transfer (LET)
The average energy deposited per unit of length of path traveled.
Linear Energy Transfer (LET)
X-rays and Gamma rays are forms of low/high LET radiation?
Low
This is electromagnetic radiation that is sparsely ionizing, interacts randomly, doesn't give up all of it's energy quickly, and causes damage through indirect actions
Low LET radiation
Low LET radiation causes damage primarily through the formation of free radicals which is what type of action?
indirect
What can usually reverse cellular damage caused by low LET?
repair enzymes
Alpha particles are a form of low/high LET radiation?
High
What includes particals that have substantial mass and charge that cause dense ionization and loses energy quickly?
High LET radiation
Which form of LET is more destructive to biologic tissue?
High
The probability of an electron interacting with DNA rather than an alpha particle is ___
low
These particles have a low probability of interacting with DNA because they do not interact as often and they travel farther.
electrons
These particles have a high probability of interacting with DNA because they interact often and they do not travel far.
alpha particles
Biologic damage produced by radiation ___ as the LET of radiation increases.
increases
This describes the relative capabilities of radiation with differing LETs to produce a certain biologic reaction
Relative Biologic Effectiveness (RBE)
The ratio of the dose of reference radiation to the dose that is necessary to produce the same biologic reaction.
Relative Biologic Effectiveness (RBE)
Dose in Gy from 250 kVp x-rays/ dose in Gy of test radiation (abbrev.)
RBE
As LET increases, RBE ____
increases
Low-LET have __ RBE
low
High-LET have ___ RBE
high
Diagnostic x-rays have a RBE of __?
1
Why is RBE not practical for specifying radiation protection dose levels in humans?
cells and tissues differ in biologic response
What is similar to RBE and used to calculate equivalent dose
Radiation Weighting Factor (Wr)
This describes the response of biologic tissue to radiation is greater when irradiated in an oxygenated state than when irradiated in an oxygen deprived state
Oxygen Enhancement Ratio (OER)
Dose required without O2/ Dose required with O2
Oxygen Enhancement Ratio (OER)
OER is most pronounced in ___ radiation
low-LET
The presence or absence of oxygen does not matter with what type of radiation?
High-LET
a solitary atom or most often a combination of atoms that behaves as an extremely reactive single entity as a result of the unpaired electrons
free radical
Free radicals dramatically ___ the amount of biologic damage
increase
The presence/absence of oxygen in tissue makes bioligic damage produced by free raddicals permaninet
presence
The presence of O2 makes damage permanent by producing ____, which makes nonrestrable changes in the chemical composition
organic peroxide compounds
Bioligic damage from ionizing radiation can be observed on which 3 levels?
molecular, cellular, and organic
The structures of a cell's constituent molecules determines ___
cell function
Exposure to radiation can alter cell structures and disturbe the cell's ____ & ultimately the way it operates
chemical balance
Irradiation of ____ ___ may disrupt body processes
somatic cells
Irradiation of ____ ___ may be passed to future generations in the form of genetic mutations
genetic cells
When radiation interacts with a cell, ionizations or excitations occur in ___ or ____?
DNA or water
The action of radiation on the cell is classified based on the ___ __ _____.
site of interaction
interaction with master molecules (DNA)
Direct action
interaction that occurs in water molecules
indirect action
This type of action may occur after exposure to any type of radiation but is MUCH more likely with high LET radiation
Direct
When ionizing particles interact directly with DNA, RNA, proteins and/or enzymes the reasult is breakage of ____ ____, which makes them abnormal both structurally and functionally.
chemical bonds
this typeo f action occurs when radiation interacts with water which produces free radicals
Indirect Action
If free radicals interact with DNA the damage to the DNA is what type of action?
indirect
what type of action is more likely to occur?
indirect
Indirect action involves the breakdown of a water molecule in to smaller molecules, producing what?
ions and free radicals
If an interaction with water occurs, what ion pair is formed from the water molecule?
HOH+ and e-
How much damage is caused when HOH+ and e- recombine?
none
Positive and negative water molecules are ___, or they will break apart into smaller molecules.
unstable
what makes free radicals highly reactive?
unpaired electron
if Hydrogen and hydroxyl ions recombine the form what? (no harm)
normal water molecule
What are the 4 effets of ionizing radiation on DNA?
single-strand break, double-strand break, mutation, and covalent cross-links
Which effect on DNA occurs in low LET radiations and breaks into 2 sugar-phosphate chain that repair enzymes can reverse
Single-strand Break
when a DNA breaks into 1 sugar-phosphate chain
point mutation
Which effect on DNA occurs when one ore more breaks in both sugar-phosphate chains occur and is more common with high LET.
Double-strand break
The loss or change in a nitrogenous ase on a DNA chain; the alteration of the base sequences
mutation
what is contained in the strict sequences of DNA bases?
genetic information
If the cell divides, the mutation will be transfered to how many of the daughter cells?
1 or 2
Chemical unions created beween atoms by the single sharing of one or more pair of electrons; can occur in many different forms and are potentially fatal to the cell.
Covalent Cross-Links
when changes occur in the DNA molecule what exhibits the alteration?
chromosome
What are the 3 effects of Ionizing radiation on chromosomes?
radiation-induced chromosome breaks, chromosomal fragments, and chromosomal anomalies
What may be viewed microscopically (metaphase and anaphase) and can happen to the chromosomes of somatic and germ cells?
Radiation-induced chromosome breaks
During which phases of mitosis can you view radiation-induced chromosome breaks?
Metaphase and anaphase
What is produced by chromosome breakage and have a fractured extremity that have the ability to adhere to each other?
chromosomal fragments
What are chromosome or chromatid aberrations that can be observed in metaphase?
chromosome anomalies
During which phase of mitosis can you view chromosome anomalies?
Metaphase
Chromosome anomalies that result when radiation occurs before DNA synthesis; each daughter cell exhibits this
Chromosome aberrations
Chromosome anomalies that result when radiation occurs after DNA synthesis; only 1 daughter cell exhibits the aberration
Chromatid aberrations
break rejoins with no visible damage (structural change)
Restitution
part of the chromosome or chromatid is lost at the next cell division (structural change)
Deletion
grossly mis-shapen chromosome may be reproductive without visible damage to the chromosomes (structural change)
Broken-end rearrangement
what does broken-end rearrangement result in?
mutations
Concept that DNA is the "master" molecule in a cell, andif it is inactivated by exposure to radiation, the cell will die.
target theory
Interactions occur only by ___
chance
x-ray or gamma ray doses of about 1000 Gy in a matter of seconds or minutes
Instant death
cell does not die, but cannot reproduce; 1-10 Gy
Reproductive Death
"interphase death" cells die without attempting division; occurs spontaneously in both normal tissue and in tumors
Apoptosis
The doser required to cause apoptosis is governed by the cell's
radiosensitivity
"genetic death" occurs when a cell dies after one or more divisions
Mitotic death
can occur from doses as small as .01 Gy
Mitotic Delay
a potential outcome when radiation interacts with a DNA macromolecule; can occur in one or both strands and results in a loss of genetic material
chromosome breakage
A method of displaying the sensitivity of a particular type of cell to radiation
cell survival curve
A cell survival curve for low LET radiation shows ___ change in survival at low doses
little
A cell survival curve for low LET radiaton shows a ____ in survival as dose increases (linear portion)
decrease
A curve for high LET does not have a shoulder, meaning it is ___.
irreparable
Immature cells are undifferentiated and rapidly dividing, therefore they are ___ radiosensitive.
more
Mature cells are highly differentiated and divide slowly if at all, therefore they are ___ radiosensitive.
less
LET affects cell ____.
radiosensitivity
Oxygen ___ the effects of ionizing radiation by increasing tissue radiosensitivity
enhances
Oxygen increases the ___ ____ ____ of radiation.
potential indirect damage
Established that radiosensitivity is a function of the metabolic state of the cell receiving exposre
Law of Bergonie and Tribondeau
Radiosensitivity of cells is ___ ___ to their reproductive activity.
directly proportional
Radiosensitivity of cells is ___ __ to their degree of differentiation.
inversely proportional
The most pronounced radiation effects occur in cells with the ___ maturity and specialization and the ___ reproductive activity
least, greatest
Effect of ionizing radiation on human cells that is a decrease in the number of blood cells in circulation
hematologic depression
Effect of ionizing radiation on human cells that is a decrease in the number of cells produced in bone marrow
depletion of Immature blood cells
This happens after some cells in the bone marrow recover
repopulation
among the most sensative cells of the Hematpoeitic system
erythrocytes
Humans receiving 5Gys may die within ___ __ due to depletion of stem cells of the hematopoietic system
30-60 days
stem cells are part of which system?
hematopoietic system
Dose that produces death in 50% of subjects in 30 days
LD 50/30
Dose that prodices death in 50% of subjects in 60 days
LD 50/60
Lethal dose for humans
3-4 Gy
white blood cells
leukocytes
subgroup of leukocytes that defend the body against foreign antigens by producing antibodies
lymphocytes
Lymphocytes manufactured in ___ are the most radiosensitive blood cells in the human body
bone marrow
doeses of ____ depress the number of WBC
.25 Gy
Type of WBC that plays an important role in fighting infection; dose of .5 Gy cand cause reduction
Neutrophil
Scavenger type of WBC that fights bacteria and responds to irradiation by a sudden increase in number followed by a decrease
Granulocytes
platelets that initiate blood clotting and prevent hemorrhage; .5 Gy depresses counts
Thrombocytes
Tissue found in the lining of intestines, mucous lining of respiratory tract, pulmonary alveoli, and lining of blood and lymphatic vessels that is very radiosensitive
epithelial tissue
tissue that is highly specialized, does not divide, and is relatively insensitive to radiation
muscle tissue
tissue that is more radiosensitive in the embryo/fetus than in an adult
nervous tissue
What is needed to cause temporary sterility of sperm and ova cells
2 Gy
What is needed to cause permanent sterility of sperm cells
5 or 6 Gy
Amount of radiation needed to cause permanent sterility of ova cells?
5 Gy
What is anoxic
without oxygen
what is hypoxic
low oxygen conditions
What is the OER (oxygen enhancement ratio) for xrays and gamma rays when the radiation dose is high
3.0 (the OER may be less about 2.0 when radiation does are below 2 Gy about 200 rad
What is the oxygen fixation hypothesis
Without oxygen, damage produced by the indirect action of radiation of a biologic molecule may be repaired, but when damage occurs through an oxygen-mediated process, the end result is permanent, or fixed
What 3 levels can ionizing radiation be observed
molecular, cellular, and organic
What are short wavelength, high energy waves emitted by the nuclei of radioactive substances
gamma rays
what is the process whereby single chromosome breaks rejoin in their original configuration with no visible damage
restitution
with reference to human cells and the impact of ionizing radiation on them, this is a factor that is variable
radiosensitivity
tentacle like extensions from a nerve cell body that carry impulses toward the cell
dendrites
what type of water molecule that forms when hydrogen and hydoxyl ions recombine
normal
Particle composed of two protons and two neutrons
alpha
abbreviation for important factor used in assessing potential tissue and organ damage from exposure to ionizing radiation
LET
scavenger type of white blood cells that fight bacteria
granulocytes
non specialized, rapidly dividing cells in the human body
immature
type of delay that can be caused from exposing a cell to as little as 0.01 gray (1 rad) of ionizing radiation just before it begins dividing
mitotic
what an ionized atom will not be able to do properly in molecules
bond
what may be used to expain cell death and nonfatal cell abnormalities caused by exposure to ionizing radiation
targettheory
what type of tissue considered relatively insensitive to radiation
muscle
______ action is more likely to happen after exposure to high-LET radiation
direct
enzymes that are capable of reversing damage from a single strand break in a DNA macromolecule
repair
a nonmitotic or nondivision form of cell death that occurs when cells die without attempting division during the interphase portion of the cell life cycle
apoptosis
blood cells that initiate clotting and prevent hemorrhage
Platelets
what a therapeutic dose of ionizing radiation will cause in the blood count
decrease
a long single tentacle from a nerve cell body that carries impulses away from the cell
axon
Atomic level of which biologic damage resulting from exposure to ionizing radiation begins
molecular
small head circumference
microcephaly
nerve cell
neuron
cross-link formed between two places on the same DNA strand
intrastrand
a type of breakage that is a potential outocme when ionizing radiation interacts with a DNA macromolecule
chromosome
What are effects produced by reactive free radicals, which are created by the interaction of radiation with a water molecule
indirect action
what is used to calculate the equivalent dose to determine the ability of a dose of any kind of ionizing radiation to cause biologic damage
radiation weighting factor (Wr)
States that the radiosensitivity of cells is directly proportional to their reproductive activity and inversely proportional to their degree of differentiation.
law of Bergonie and Tribondeau
What is a genetic mutation in which the chromosome is not broken but the DNA within is damaged
point mutation
What is the chemical unions created between atoms by the single sharing of one or more pairs of electrons
covalent cross links
What is the loss or change of a nitrogenous base in the DNA chain
mutation
What is OER
oxygen enhancement ratio
ratioof the radiation dose required to cause a particular biologic response of cells or organisms in an oxygen deprived environment to the dose required to cause an identical response under normal oxygenated conditions
OER
programmed cell death
apoptosis
The cell dies if inactivation of the master molecule occurs as a result of exposure to ionizing radiation is called what
target theory
lesions that result when irradiation occurs early in interphase BEFORE DNA synthesis takes place
chromosome aberrations
lesions that result when irradiation of individual chromatids occurs later in interphase, after DNA synthesis takes place
chromatid aberrations
chromosome aberations happen when irradiation occurs in what phase
early in interphse
what may be used to expain cell death and non fatal cell abnormalities caused by exposure to radiation
target theory
what describes 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 required to cause an identical response under normal oxygenated conditions
OER
ring chromosomes, dicentric chromosomes, and anaphase bridges are examples of what?
distorted chromosomes (in broken-end rearrangement)
For radiation protection purposes what kind of radiation is of the greatest concern when internal contamination is possible
high LET
Because the ovaries of young women are less sensitive than those of older women, what kind of dose of radiation is required to cause sterility in young women
a higher dose of radiation
Reproductive death generally results from exposure of cells to doses of ionizing radiation in the range of what
1 to 10 gray (100 to 1000rad)
What ions usually recombine to form a normal water molecule the existence of these ions as free agents in the human body is insignificant in terms of biologic damge
hydrogen and hydroxyl ions
Part of the chromosome or chromatid is lost at the next cell division, creating an aberration known as what
acentric fragment (deletion)
In apoptosis the cell shrinks and produces tiny membrane-enclosed structures called what
blebs
LD of what is more practical for human beings than LD 50/30
LD 50/60
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