Chapter 7- Molecular and Cellular Radiation Biology Flashcards
Branch of biology concerned with the effects of ionizing radiation on living systems
Radiation Biology
what does Radiation Biology include of:
Sequence of events occurring after the absorption of energy from ionizing radiation
Action of the living system to make up for the consequences of this energy assimilation
Injury to the living system that may be produced
Damages living systems by ionizing the atoms comprising the molecular structure of these systems
IONIZING RADIATION
Biologic damage begins with the ionization produced by various types of radiation such as
Xrays
Gamma rays
Alpha particles
Beta particles
Protons
TRUE OR FALSE:
Ionized atoms will not bond properly in molecules
True
what varies among the different types of radiation
Charge, mass, and energy vary among the different types of radiation
**These attributes determine the extent to which different radiation modalities transfer energy into biologic tissue.
Three important concepts help us to understand the way ionizing radiation causes injury and how the effects may vary in biologic tissue.
Linear energy transfer
Relative biologic effectiveness
Oxygen enhancement ratio
The average energy deposited per unit length of track by ionizing radiation as it passes through and interacts with a medium along its path
Linear Energy Transfer (LET)
What does LET stand for
Linear Energy Transfer
what units is LET described in
Is described in units of keV/μm
Is a very important factor in assessing potential tissue and organ damage from exposure to ionizing radiation
LET
Radiation categories according to LET
Low-linear energy transfer radiation
High-linear energy transfer radiation
Examples of Low LET radiation
Gamma Rays and Xrays
Examples of high LET Radiation
-alpha particles
-ions of heavy nuclei
-charged particles released from interactions between neutrons and atoms
-low energy neutrons
Describes the relative capabilities of radiation with differing LETs to produce a particular biologic reaction
Relative Biologic Effectiveness (RBE)
What does RBE stand for
Relative Biologic Effectiveness
is the ratio of the dose of a reference radiation (conventionally 250-kVp x-rays) to the dose of radiation of the type in question that is necessary to produce the same biologic reaction in a given experiment. The reaction is produced by a dose of the test radiation delivered under the same conditions.
RBE of the type of radiation being used
The ratio of the radiation dose required to cause a particular biologic response of cells or organisms in any oxygen-deprived environment to the radiation dose required to cause an identical response under normal oxygenated conditions
Oxygen Enhancement Ratio (OER)
when the radiation dose is high, how much OER does xrays and gamma rays have
In general, x-rays and gamma rays have an OER of about 3.0 when radiation dose is high.
when the radiation dose is low, how much is the OER
ER may be less (approximately 2.0) when radiation doses are below 2 Gyt.
what is the OER ratio
radiation dose required to cause biologic responce without O2 over Radiation dose required to cause biologic response with O2
In living systems, biologic damage stemming from exposure to ionizing radiation may be observed on three levels
Molecular
Cellular
Organic systems
Any visible radiation-induced injuries of living systems at the cellular or organic level always begin with damage at what level
at the molecular level.
results in the formation of structurally changed molecules that may impair cellular functioning.
Molecular Damage
what is the relationship between LET and RBE
directly proportional
As LET increases, what happens to the biologic damage
LET increases, biologic damage increases
what happens to the energy as there is an increase in LET and increase in RBE
decrease in energy
what happens to energy when there is a decrease in LET and RBE
increase in energy
Is low LET less or more damaging than High LET
Low LET is less damaging because there is not as much deposited.
which term means most sensitive
least resistant
which term means least sensitive
most resistant
what is the RBE ration
Dose in Gy over the dose of test radiation
Somatic
yourself
Genetic
future generations
Three things that can happen in the molecular, cellular, or organic systems
-repair (no damage)
-mutated
-cell death
Because energy from ionizing radiation can alter a human cell’s constituent molecules, such exposure may disturb the cell’s chemical balance and ultimately the way it operates. The affected cell can then no longer perform its normal task.
If a sufficient quantity of somatic cells are affected, entire body processes may be disrupted.
If radiation damages the germ cells, the damage may be passed on to future generations in the form of genetic mutations.
Effects of Irradiation on Somatic and Genetic Cells
There are two classifications of ionizing radiation interaction on a cell.
Direct action (e.g., in DNA)
Indirect action (e.g., in H2O)
directly hitting DNA (more common with Alpha)
Direct
is high LET direct or indirect
direct
hitting something else not DNA
indirect
is low LET direct or indirect
indirect
is direct or indirect more likely to happen
Indirect —-Because the human body is 80% water and less than 1% DNA, essentially all effects of low-LET irradiation in a living cell result from indirect action.
what happens when free radicles comes in contact with DNA
there will be cell death
what does a indirect hit create
indirect hit creates free radicals, those free radicals cause more biological damage
What are the steps of Radiolysis of water
Ionization of water molecules
Production of free radicals
Production of undesirable chemical reactions and biologic damage
Production of cell-damaging substances
Organic free radical formation
only effecting the one side of rungs
single strand
-can be cell death (not commonly repaired)
-usually happens with alpha
Double strand break
Ionizing radiation interacts with DNA macromolecule, transfers energy, and ruptures one of the molecule’s chemical bonds possibly severing one of the sugar-phosphate chain side rails (called a point mutation)
Repair enzymes are often capable of reversing this damage
single strand break
what type of radiation does Double strand break happen with
Occur more commonly with densely ionizing (high-LET) radiation.
Further exposure of the affected DNA macromolecule to ionizing radiation can lead to additional breaks in the sugar-phosphate molecular chain(s).
Breaks may also be repaired but are not repaired as easily as single-strand breaks.
If repair does not take place, further separation may occur in the DNA chains, threatening the life of the cell.
Double strand break
what terms means between same dna strand
intrastrand cross link
what term means between two different strands
interstrand cross link
Result is a cleaved or broken chromosome with each new portion containing an unequal amount of genetic material
If damaged chromosome divides, each new daughter cell will receive an incorrect amount of genetic material culminating in the death or impaired functioning of the new daughter cell.
double strand break in same rung of dna
Interactions of ionizing radiation with DNA molecules may cause the loss of or change in a nitrogenous base in the DNA chain.
Mutation
Direct consequence of this damage is an alteration of the base sequence,
a mutation
consequences for the cell
If cell remains viable, incorrect genetic information will be transferred to one of the two daughter cells when the cell divides.
Mutation