Ch. 7- Molecular and Cellular Radiation Biology

radiobiology

branch of biology concerned with effects of ionizing radiation on living systems

cellular

potentially harmful effects of ionizing radiation on living systems occur primarily at the _____ level

ionization

process of removing electrons from atoms composing biologic structures

linear energy transfer (LET)

average energy deposited by ionizing radiation per unit length of travel through matter

3 keV

estimated LET of diagnostic x-rays

low

diagnostic x-rays are considered ____- LET radiation

energy

amount of ionization produced in an irradiated object is related to the amount of _____ it absorbs

increases

as LET increases, the chance of a significant biologic response in DNA ______

wave-particle duality

theory that x-rays and gamma rays can behave as both waves and particles

low-LET

repair enzymes can usually repair damage caused by _____ radiation

high

alpha particles are a form of ____- LET radiation

high

____- LET radiation does not travel very far in matter, but is much more likely to produce significant damage

high-LET

DNA interactions are much more likely with _____ radiation

relative biologic effectiveness (RBE)

the capability of different types of LET to produce biologic damage

oxygen enhancement ratio (OER)

ratio of radiation dose required to produce a certain response without oxygen as compared to when oxygen is present

high-LET

due to its inherent destructive nature, oxygen has no effect on the amount of damage done by _____ radiation

free radicals

highly reactive, unstable molecules with unpaired valence electrons that seek stability by stealing from other molecules

increases

the amount of biologic damage _____ with the presence of free radicals

direct

when ionization occurs on the DNA molecule itself, this is known as _____ action

indirect

when ionization occurs on a distant, noncritical molecule that transfers energy to DNA, this is known as ______ action

indirect

it is assumed that almost all biologic effects from ionizing radiation are ______ effects

oxygen

when ______ is present, biologic effects are amplified

radiolysis

the dissociation of water molecules after interaction with ionizing radiation

hydrogen

if a positive water molecule decomposes, it can form a ______ ion

hydroxyl

hydrogen ion + oxygen = _____ radical

point lesions

single strand breaks in DNA molecules that can result in mutations or death

hydrogen peroxide

substance formed from combination of two hydroxyl free radicals and is poisonous to the cell

single

_____-strand DNA breaks commonly occur with low-LET radiation

double

______-strand DNA breaks commonly occur with high-LET radiation

mutation

the loss or change of a base in the DNA chain

cross-linking

covalent ________ occurs when two or more molecules are joined together by a covalent bond

intrastrand

______ cross-linking occurs on the same DNA strand

interstrand

________ cross-linking occurs between two different DNA molecules

restitution

broken DNA strands rejoin and no damage occurs

deletion

cell mutation in which part of a chromosome or chromatid is lost during the next cell division

target theory

concept that radiation damage to sensitive cellular components comes from random “hits” to critical targets such as DNA

DNA

the target molecule

random

the interaction between ionizing radiation and DNA is considered to be ______

inactivated

according to the target theory, cell death only occurs if the target molecule is _______

apoptosis

form a cell death that occurs when a cell dies during interphase before it can divide

mitotic death

form of cell death that occurs after the cell has divided one or more times

mitotic delay

a temporary halt in mitosis due to exposure to ionizing radiation

Law of Bergonie and Tribondeau

states that the sensitivity of cells to radiation is related to their reproductive activity and degree of differentiation. Highly mitotic and less differentiated cells are more susceptible.

radioresistant

muscle cells are considered to be relatively ______

radiosensitive

reproductive cells are considered to be relatively _______