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:
- 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
is a complex interconnected living system composed of very large numbers of various types of cells, most of which may be damaged by radiation.
The human body
Damages living systems by ionizing the atoms comprising the molecular structure of these systems
Ionizing radiation
what does ionization mean?
removal of an electron
free radicals are considered your what
your biological damage
Biologic damage begins with the ionization produced by various types of radiation such as:
- x-rays
- gamma rays
- alpha particles
- beta particles
- protons
Ionized atoms will not what?
ionized atoms will not bond properly in molecules
x-rays are considered
man made and can penetrate through more
gamma rays, alpha particles, and beta particles are considered
natural
Can only travel so far
- effect heavier
- more superficial can’t penetrate
alpha particles
is composed of two protons and two neutrons and therefore carries an electric charge of +2
has a number of 20
Alpha particles
what charge do electrons have?
electrons have a negative charge
What 3 things varies among the different types of radiation?
- charge
- mass
- energy
*These attributes determine the extent to which different radiation modalities transfer energy into biologic tissue.
What are the three important concepts that help us to understand the way ionizing radiation causes injury and how the effects may vary in biologic tissue?
- Linear energy transfer (LET)
- Relative biologic effectiveness (RBE)
- Oxygen enhancement ratio (OER)
What kind of relationship does LET and RBE have?
directly proportional
AS LET increases
RBE also increases
As LET increases
biological damage also increases
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
1 micron [µm] =
10 ^−6 m
Examples of Low LET radiation:
-X-rays
- Gamma Rays
- Electrons
Low LET has?
Low RBE
Higher energy
Low LET are able to
pass through not a lot is deposited less damaging
Examples of high LET Radiation:
-alpha particles
-ions of heavy nuclei
-charged particles released from interactions between neutrons and atoms
-low energy neutrons
High LET has
high RBE
less energy
High LET is
deposited energy as it goes through its path more damaging
When LET increases, the chance of a significant biologic response in the radiosensitive DNA macromolecule also
increases
Because of a property known as wave-particle duality, x-rays and gamma rays, can also be referred to as streams of moving particles called photons, each of which has
no mass* and no charge
When low-LET radiation interacts with biologic tissue, it causes damage to a cell primarily through an indirect action that involves the production of molecules called
free radicals
Because low-LET radiation generally causes sub-lethal damage to DNA,
repair enzymes can usually reverse the cellular damage.
High-LET radiation includes particles that possess substantial:
mass and charge.
For radiation protection, high-LET radiation is of most significant concern when internal contamination is possible, that is, when a radionuclide has been:
- Implanted
- Ingested
- Injected
- Inhaled
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
What is the mathematical expression for RBE?
RBE= dose in Gyt from 250 kvp x-rays (reference radiation) over dose in Gyt of test radiation
math equation for RBE
bigger number over smaller number
least resistant means
most sensitive
Most resistant means
least sensitive
the concept of RBE alone is not practical for specifying radiation protection dose levels in humans. To overcome this limitation, a radiation weighting factor (WR) is employed to calculate the equivalent dose (EqD) to determine the ability of a dose of any kind of ionizing radiation to cause biologic damage.
True or false
True
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.
the more oxygen that is present in the cell
the more sensitive it is to radiation
What is the OER ratio
radiation dose required to cause biologic responce without O2 over Radiation dose required to cause biologic response with O2
OER math formula
without oxygen over with oxygen
without oxygen is called
anoxic
low oxygen
hypoxic
cells that are anoxic are
3x more resistent least sensitive
high LET have an OER of
1.0
blood cells have a lot of oxygen meaning
they are more sensitive
blood cells have a count of
0.25
blood cells are easily repaired but once they get to the muscle tissue
they are not easily repaired
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 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
somatic
yourself
genetic
future generations
Three things that can happen in the molecular, cellular, or organic systems:
- it can be repaired if there’s no damage
- it can be repaired but (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.
Effects of Irradiation on Somatic and Genetic Cells
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.
Cells of the human body are highly what? Each cell has a predetermined task to perform, and each cell’s function is governed and defined by the structures of its constituent molecules.
highly specialized
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 particles)
Direct action
is high LET direct or indirect
direct action
hitting something else not DNA more likely to get because our body is made of 80% of water
indirect action
is low LET direct or indirect
indirect action
when you have an indirect hit you create what
free radicals which creates biological damage
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
most common form of biological damage
free radicals
biological damage occurs as a result of DNA inaccurate / functioning high LET
direct action
most are these interact with water ( 80 to 85 %) produce free radicals
indirect action
refers to the dissociation of molecules by ionizing radiation
Radiolysis
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
when it hits the water molecule it can ionize that water molecule if that happens there’s no damage it can restabilize
ionization of water moleucles
ionization of water molecules has a charge of
positive charge
free radical is what kind of charge
negative charge
they are unstable and can break apart into smaller molecules
production of free radicals
radiation with water can form
ion pair
2/3ths of your radiation damage is caused by your
free radical
2/3ths of your radiation damage is caused by your free radical
production of undesirable chemical reactions and biologic damage
altered areas of chemical bond
point lesions
free radical hydroxyl
OH
hydrogen peroxide
production of cell damaging substances
chemical symbol for hydrogen peroxide
OH + OH = H2O2
hydrogen peroxide in the body is
extremely damaging when it comes to radiation cellular damage
very poisonous to the cell
hydrogen peroxide
are believed to be among the primary substances that produce biologic damage directly after the interaction of radiation with water.
hydroperoxyl radical and hydrogen peroxide
small scale change of disruption original molecule is destroyed and is replaced by radicals
organic free radical formation
only effecting the one side of rungs (DNA)
single 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
a single alteration along the sequence of nitrogenous bases can result in
a gene abnormality
Point lesions commonly occur with
Low-LET radiation
-can be cell death (not commonly repaired)
-usually happens with alpha what type of break?
double strand break
one chemical find side rail on strand
point mutation
low LET
repair enzyme can repair
DNA single strand break
high LET
not usually repaired what type of break?
double strand break
