Radiobiology chapter 7
The _______________ particle, which is composed of two protons and two neutrons and therefore carries an electric charge of +2 strongly attracts the negatively charged electrons as it passes.
Alpha
Examples of high LET radiation are : ________________________, ________________________________, ___________________________________________
Alpha particles, -Ions of heavy nuclei -Charged particles released from interactions between neutrons and atoms
In apoptosis the cell shrinks and produces tiny membrane-enclosed structures called _______________.
Blebs
______________________________________ a grossly misshapen chromosome may be produced. Ring chromatids, dicentric chromosomes, and anaphase bridges are examples of such distorted chromosomes and chromatids.
Broken-end Rearrangement
____________________________________________ whereby the chromatids genetic material has been rearranged yet the chromatid appears normal. Translocations are examples of such rearrangements.
Broken-end rearrangement without visible damage to the chromatids
____________________ cell death occurs when a cell dies after one or more divisions.
Mitotic Death
Exposing a cell to as little as 10 cGy of ionizing radiation just before it begins dividing can result in _________________________ the failure of the cell to start dividing on time.
Mitotic Delay
The loss or change of a base in the DNA chain represent a __________________________.
Mutation
DNA molecules can also become covalently linked to a protein molecule, these linkages are potentially _____________ to the cell if they are not correctly repaired.
Fatal
A ____________________ is a molecular unit that has no net electrical charge but, because of having an unpaired valence electron, it is an extremely reactive entity.
Free radical
_____________________ are solitary atoms for example, a non-molecular hydrogen atom (H) or most often a combination of atoms such as (OH) that behave as single entities and are chemically reactive as a result of the presence of unpaired valence electrons.
Free radicals
____________________________ exhaust their energy rapidly in matter unless they are of extremely high energies, they cannot travel or penetrate as far as x-ray and gamma ray photons.
High LET radiation
Direct action is much more likely to occur after exposure to _______________________ radiation such as alpha particles, which produce a vast number of ionizations in a very short distance of travel.
High-LET
(H2O2) is also known as _________________________.
Hydrogen Peroxide
A hydroxyl radical (OH*) can bond with another hydroxyl radical (OH*) and form __________________________________ which is a substance that is very poisonous to the cell.
Hydrogen peroxide (OH* + OH* = H2O2)
(HO2*) is also known as _______________________.
Hydroperoxyl radical (HO2*)
________________________________ is formed when a hydrogen free radical (H*) combines with molecular oxygen (O2).
Hydroperoxyl radical (HO2*)
Approximately two thirds of all radiation-induced damage is believed to be ultimately caused by ____________________________.
Hydroxyl free radical (OH*)
(OH*) is also known as ________________________.
Hydroxyl radical
A neutral oxygen-hydrogen combination is called a ________________________.
Hydroxyl radical (OH*)
Essentially all effects of low LET irradiation in living cells result from ________________________.
Indirect action
________________________ is always a multi-stage process that first involves the production of free radicals that are usually created by the interaction of the radiation with water molecules.
Indirect action
Cross-linking may occur between complimentary DNA strands or between entirely different DNA molecules this is called _________________________ cross-linkng.
Interstrand
Cross-linking between two different places on the same strand of DNA is called a ________________________ cross-link.
Intrastrand
LET is usually described in units of __________________________________
Kiloelectron volts (keV) per micron
The ___________________________________ 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
The __________________________________ is calculated by dividing the total energy deposited in the medium by the total length of the track.
Linear Energy Transfer (LET)
The average energy deposited per unit length of track is _____________________________________.
Linear Energy Transfer (LET)
Point lesions commonly occur with _______________ radiation.
Low LET
___________________________, which carry no electrical charge are also a form of high LET radiation.
Low-energy neutrons
An _______________________ is any organic compound with two oxygen atoms joined together.
Organic peroxide
If __________________ is present when a tissue is irradiated, more free radicals will be formed in the tissue; this increases the indirect damage potential of the radiation.
Oxygen
The ___________________________________ refers to the enhancement of the therapeutic or detrimental effect of ionizing radiation due to the presence of oxygen.
Oxygen Enhancement Ratio (OER)
____________________________________ describes the comparative capabilities of radiation with differing LETs to produce a particular biologic reaction.
Relative Biologic Effectiveness (RBE)
The process of healing by ____________________ is believed to be how 95% of single-chromosome breaks mend.
Restitution
_______________________ the chromosome breaks rejoin in their original configuration with no visible damage. No injury to the cell occurs.
Restitution
A positively charged water molecule (HOH+) may recombine with an electron to reform a ___________________________.
Stable water molecule
The concept of radiation damage to specific sensitive locations resulting from discrete and random events is known as __________________________.
Target Theory
Reproductive death generally results from exposure of cells to doses of ionizing radiation in the range of ___ to ____ Gy.
1-10 Gy
When LET increases, the chance of producing a significant biologic response in the radiosensitive DNA macromolecule also _____________________.
increases
LET is calculated by dividing the total energy deposited in the medium by the total length of the ________________.
track
When passing through a medium such as human tissue, ionizing radiation may interact with that medium during its passage and as a result lose its energy along its path called a _______________
track
________________ and ________________ ray photons can impart energy to orbital electrons in atoms if the photons happen to pass near the electrons
x-ray and gamma
(HOH-) becomes a _______________________ and a _______________________.
- Hydroxyl ion (OH-) - Hydrogen radical (H*)
When tissue is irradiated in an oxygenated state, the tissue is more sensitive to radiation than when it is exposed to radiation under _________________ or __________________ conditions.
-Anoxic (without oxygen) -Hypoxic (Low oxygen)
Two types of chromosome anomalies have been observed they are: __________________ and ___________________.
-Chromosome aberrations -Chromatid aberrations
Vital biologic macromolecules include: ______________________, ____________________, _________________________, __________________________.
-DNA -RNA -Enzymes -Proteins
HOH+ decomposes into a ____________________ and ______________________.
-Hydrogen Ion (H+) -Hydroxyl radical (OH*)
The ________________________________ and ____________________________ are believed to be among the primary substances that produce biologic damage directly after the interaction of radiation with water.
-Hydroperoxyl radical (HO2*) -Hydrogen peroxide (H2O2)
When low-LET radiation interacts with biologic tissue, it causes damage to a cell primarily through an ________________ action that involves the production of molecules called __________________________.
-Indirect -Free Radicals
To be able to understand how ionizing radiation causes injury and how the effects can vary in biologic tissue, three essential concepts must be studied: _____________________________________________, _____________________________________, and _____________________________________.
-Linear energy transfer -relative biologic effectiveness -oxygen enhancement ratio
After irradiation and during cell division some radiation induced chromosome breaks may be viewed microscopically during the ____________________ and ___________________ stages of the cell division cycle, when the length of the chromosome is visible.
-Metaphase -Anaphase
Both ______________ and _____________________ cells are subject to chromosome breaks induced by radiation.
-Somatic -Reproductive
The most pronounced radiation effects occur in cells with the : -________________________________________ -________________________________________ -________________________________________
-The least maturity & specialization - Greatest reproductive activity - Longest mitotic phases
High-energy charged particles such as _____________ and _______________ particles and _________________ also may ionize atoms by interacting electromagnetically with orbital electrons.
-alpha and beta particles -protons
Chromatid aberration leads to ___________ daughter cell(s) being affected.
1
The OER of high LET radiation is approximately equal to ________.
1
A free radical exists for approximately _______________________ before pairing up with another electron, even if to do this it has to break a chemical bond in a vital molecule.
1 millisecond
The body is less than ______ DNA
1%
The alpha particle is ________________ times the LET of the electron.
1000
Instant death of large numbers of cells occurs when a volume is irradiated with an x-ray or gamma-ray dose of ___________________ in seconds or a few minutes.
1000Gy
X-rays and gamma rays, which are low LET types of radiation, have an OER of approximately ______________ when the radiation dose is high.
3
The rate of transfer of energy from ionizing radiation, used for diagnostic purposes (x-rays), to soft biologic tissue is estimated to be __________________which is considered to be relatively low LET radiation compared with other types of radiation.
3 keV/um
Deletion, a part of the chromosome or chromatid is lost at the next cell division, thus creating an aberration known as an _____________________________ which results in a cell mutation.
Acentric fragment
It should be noted that the phenomenon of apoptosis is considered by many to be integrally related to the ________________________.
Ageing process
A classic method of displaying the sensitivity of a particular type of cell to radiation is the _____________________________
Cell survival curve
Solitary ____________________________________, result when irradiation of individual chromatids occurs later in interphase, after DNA synthesis has taken place.
Chromatid aberrations
With a double strand break in the same rung of the DNA ladder-like structure, complete _____________________________ occurs.
Chromosome Breakage
_________________________ result when irradiation occurs early in interphase, before DNA synthesis takees place.
Chromosome aberration
__________________________ in this situation the break caused by ionizing radiation is in a single strand of chromatin, which is the original chromosome.
Chromosome aberration
____________________________________ is the process of chemically joining two or more molecules by a covalent bond, which is the sharing of one or more pairs of electrons between the molecules.
Covalent cross-linking
_____________________ a part of the chromosome or chromatid is lost at the next cell division.
Deletion
In __________________________, biologic damage occurs as a result of the ionization of atoms on essential molecules produced by an immediate interaction with incident radiation.
Direct action
Also but much less likely the low LET radiation may _________________ induce single-strand breaks in the ladder like DNA structure.
Directly
The ____________________________________ is the ratio of the radiation dose required to cause a particular biologic response of cells in an oxygen-deprived environment to the radiation dose required to generate an identical response under normal oxygenated conditions.
Oxygen Enhancement Ratio (OER)
Without oxygen, the damage created by the indirect action of radiation on a biologic molecule may be repaired, but when damage occurs through an oxygen-mediated process, the final result is lasting or fixed, this phenomenon is called the ________________________________________.
Oxygen fixation hypothesis
______________________ are altered areas caused by the fracturing of a single chemical bond.
Point lesions
________________________ is the branch of biology concerned with the effects of ionizing radiation on living systems.
Radiobiology
________________________ refers to the dissociation of molecules by ionizing radiation.
Radiolysis
Identical doses of radiation of different LET's do not render identical biologic effects. True or False?
True
Cells that are _________________ are about three times more resistant than cells that are well oxygenated at the time of irradaition.
anoxic
A non-mitotic or non division form of cell death that occurs when cells die without attempting division during the interphase portion of the cell life cycle is ______________________
apoptosis
The characteristics of ionizing radiation vary among different types of radiation. Characteristics include: _________________, _________________, and _______________.
charge mass and energy
These attributes determine the extent to which different radiation modalities transfer energy into biologic tissue. __________________, ________________, and ____________________.
charge mass and energy
For low LET radiation a significant fraction of bioeffects are caused by indirect actions in which a _____________________ is formed.
free radical
Biologic damage produced by radiation __________________ as the LET of radiation increases.
escalates
High LET radiation includes particles that possess substantial ________________ and ________________.
mass and charge
Because low-LET radiation generally causes ________________ damage to DNA, repair enzymes can usually reverse the cellular damage.
sublethal