bio chapter 7 reading

-flashcards made while reading the chapter!!!

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

radiation biology

areas of study included in radiation biology are:

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, and injury to the living system that may be produced

potentially harmful effects of ionizing radiation on living systems occur primarily ____.

at the cellular level

examples of high energy charged particles.

alpha and beta particles and protons

an ionized atom does/does not bond properly in molecules.

does not

characteristics of ionizing radiation include:

charge, mass, and energy

the average energy deposited per unit length of track

linear energy transfer (LET)

LET is generally described in units of ____.

keV per micron

1 micron =

10^-6 m

the rate of transfer of energy from ionizing radiation used for diagnostic purposes to soft biologic tissue is estimated to be ___.

3 keV/micron

the LET value of the radiation involved is a very important factor in assessing ___?

potential tissue and organ damage from exposure to that type of ionizing radiation

when LET increases, the chance of producing a significant biologic response in the radiosensitive DNA macromolecule ___.

also increases

low-LET radiation is ____.

electromagnetic radiation

examples of low LET

x-rays and gamma rays

stream of particles called ____ that have no mass and no charge

photons

when low-LET radiation interacts with biologic tissue, it causes damage to a cell primarily through a(n) ___ action.

indirect

when low-LET radiation interacts with biologic tissue, it causes damage to a cell primarily through an indirect action that involves the production of ____.

free radicals

how might low-LET directly act?

may induce single strand breaks in the ladder-like DNA structure

because low-LET radiation generally causes sublethal damage to DNA, ….

repair enzymes can usually reverse the cellular damage

high-LET radiation includes particles that possess substantial:

mass and charge

examples of high-LET radiation.

alpha particles, ions of heavy nuclei, beta particles

the LET for the alpha particle is ____ the LET of the electron.

1000 times

what happens each time the particle interacts with DNA?

loses some energy and slows down in the cell

high-LET radiation is of greatest concern when internal contamination is possible, that is, when a radionuclide has been…

implanted, ingested, injected, or inhaled

a double-strand break in the same rung of the DNA ladder-like structure, complete ____ occurs.

chromosome breakage

describes the relative capabilities of radiation with differing LETs to produce a particular biologic reaction

relative biologic effectiveness (RBE)

without oxygen

anoxic

low-oxygen

hypoxic

when irradiated in an oxygenated, or aerobic, state, biologic tissue is more sensitive to radiation than when it is exposed to radiation under anoxic or hypoxic conditions

oxygen effect

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

oxygen enhancement ratio (OER)

in general, low-LET types of radiation have an OER of approximately ___ when radiation dose is high.

3.0

the OER may be less when radiation doses are ___.

lower than 2 Gyt

the OER of high-LET radiation is approximately ___.

equal to 1

what could happen if radiation damages the germ cells?

the damage may be passed on to future generations in the form of genetic mutations

the addition of energy to a molecular system that raises it from a ground state to a higher-energy state

excitation

when ionizing particles interact with a vital biologic macromolecule such as DNA

direct action

when ionizing particles interact with a water molecule, thus resulting in the creation of ions and reactive free radicals

indirect action

when ionizing particles interact directly with vital biologic macromolecules, damage occurs from ___.

the absorption of energy through Compton or photoelectric interactions

when x-ray photons interact with and ionize water molecules contained within the human body, it can result in their separation into other molecular components

radiolysis of water

what does the interaction of radiation with water ultimately result in?

an ion pair (H+ and OH-) and two free radicals (H* and OH*)

because the hydrogen and hydroxyl ions usually recombine to form a normal water molecule, the presence of these ions as free agents within the human body is ____ in terms of biologic damage.

insignificant

approximately two-thirds of all radiation induced damage is believed to be ultimately caused by the _____.

hydroxyl free radical (OH*)

believed to be among the primary substances that produce biologic damage directly after the interaction of radiation with water

H02* and H2O2

why are essentially all effects of low-LET irradiation in living cells a result of indirect action?

because the human body is 80% water and less than 1% DNA

point lesions commonly occur with ____.

low-LET

one or more breaks in each of the two sugar-phosphate chains

double-strand break

double-strand breaks happen more commonly with ____

high-LET (densely ionizing radiation)

a double strand break in the same rung of the DNA molecular structure causes ___.

complete chromosome breakage

if the damaged chromosome divides, what will happen?

each new daughter cell will receive an incorrect amount of genetic material

interactions of ionizing radiation with DNA molecules may cause the loss of or change in a nitrogenous base on the DNA change; alteration of base sequence

mutation

chemical unions created between atoms by the single sharing of one or more pairs of electrons

covalent cross-links

after irradiation and during cell division, some radiation-induced chromosome breaks may be viewed microscopically. these changes are manifested during the ___ and ____ of the cell division cycle.

metaphase and anaphase

after chromosome breakage, two or more chromosomal splinters are produced. these broken fragments can:

rejoin in their original configuration, fail to rejoin and create an aberration, or join to other broken ends and thereby create new chromosomes

what are the 2 types of chromosome anomalies that have been observed at metaphase?

chromosome aberrations and chromatid aberrations

chromosome aberrations and chromatid aberrations have been observed at ____.

metaphase

chromosome aberrations result when ____.

irradiation occurs early in interphase, before DNA synthesis takes place

solitary chromatid aberrations result when ____

irradiation of individual chromatids occur later in interphase, after DNA synthesis takes place

whereby the breaks rejoin in their original configuration with no visible damage; no injury to the cell occurs because the chromatid has been restored

resitution

whereby a part of the chromosome or chromatid is lost at the next cell division, thus creating an aberration known as an acentric fragment; results in cell mutation

deletion

whereby a grossly misshapen chromosome may be produced; results in cell mutation

broken-end rearrangement

examples of distorted chromosomes and chromatids from broken-end rearrangement

ring chromatids, dicentric chromosomes, and anaphase bridges

whereby the chromatid’s genetic material has been rearranged even though the chromatid appears normal; results in cell mutation

broken-end rearrangement without visible damage to the chromatids

examples of broken-end rearrangement without visible damage to the chromatids.

translocations

affected locations in a cell or, more specifically, on a vital molecule within the cell are known as ___.

targets

concept of radiation damage that it appears that producing a serious effect usually requires more than one radiation “hit” on a specific target

target theory

a _____ that maintains normal cell function is believed to be present in every cell and is vital the cell. is presumed to be ____.

master (or key) molecule; DNA

what are the 6 ways the damage to the cell’s nucleus is revealed?

instant death, reproductive death, apoptosis, mitotic (genetic) death, mitotic delay, interference with function

programmed cell death

apoptosis

occurs when a volume is irradiated with x-ray or gamma ray dose of approximately 1000 Gyt in a period of seconds or a few minutes

instant death

generally results from exposure of cells to doses of ionizing radiation in the range of 1 to 10 Gyt; cell doesn’t die, but permanently loses its ability to procreate

reproductive death

form of cell death that occurs when cells die without attempting division during the interphase portion of the cell life

apoptosis

apoptosis occurs ____.

spontaneously in both normal tissue and in tumors

example of apoptosis.

during embryonic development when tadpoles lose their tails

in apoptosis, the cell shrinks and produces tiny membrane-enclosed structures called ____.

blebs

it appears that the more radiosensitive the cell is, the _____ required to cause apoptotic death

smaller the dose

_____ follows permanent inhibition.

cell death

occurs when a cell dies after one or more divisions

mitotic (genetic) death

the radiation dose required to produce mitotic death is ______.

less than the dose needed to produce apoptosis in slowly dividing/nondividing cells

exposing a cell to as little as ____ of ionizing radiation just before it begins dividing can cause mitotic delay.

0.01 Gyt

the failure of the cell to start dividing on time

mitotic delay

possible reasons for mitotic delay:

alteration of a chemical involved in mitosis, proteins required for cell division not being synthesized, a change in the rate of DNA synthesis after irradiation

classic method of displaying the sensitivity of a particular type of cell to radiation is the ___.

cell survival curve

examples of radiosensitive cells

basal cells of the skin, lymphocytes/erythrocytes, intestinal crypt cells, germ cells

examples of radiosensitive cells

brain cells, muscle cells, nerve cells

if oxygen is present when a tissue is irradiated, ____ will be formed in the tissue; this increases the ____ potential of the radiation.

more free radicals; indirect damage

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

how does ionizing radiation adversely affect blood cells?

by depressing the number of cells in the peripheral circulation

a whole body dose of ____ delivered within a few days produces a measurable hematologic depression.

0.25 Gyt

most blood cells are manufactured in ____.

bone marrow

____, also known as RBC’s are among the most radiosensitive of human cells.

erythrocytes

an immature cell of bone marrow that is the most basic precursor of granulocyte white blood cells

myeloblasts

the lethal dose in human beings is usually given as ____.

LD 50/60

the lethal whole-body dose is generally estimated to be ____ without treatment and higher if medical intervention is available.

3.0-4.0 Gyt

white blood cells are collectively called ____.

leukocytes

belong to the granule-free category and are of major importance in defending the body against foreign objects by producing protective proteins to combat disease

lymphocytes

the most radiosensitive blood cells in the human body

lymphocytes

the normal white blood cell count for an adult ranges from _____.

5,000 to 10,000/mm³

initiate blood clotting and prevent hemorrhage

thrombocytes (platelets)

____ lines and covers the body tissue.

epithelia tissue

epithelial tissue is devoid of blood vessels and it regenerates through the process of ___.

mitosis