Cellular Effects of Radiation: Key Concepts and Cell Cycle Dynamics

Cellular Effects of Radiation

The study of how ionizing radiation affects cells and their structures.

Radiosensitivity

The relative susceptibility of cells to radiation damage.

Radioresistance

The ability of cells to resist or tolerate radiation damage.

Undifferentiated cells

Immature cells that have not yet developed specialized functions; generally more radiosensitive.

Differentiated cells

Mature, specialized cells; generally more radioresistant.

Stem cells

Undifferentiated cells capable of developing into specialized cell types.

Precursor cells

Immature cells that develop into more specialized or mature cells.

Law of Bergonie and Tribondeau

Cells are generally more radiosensitive when they are highly proliferative, less differentiated, and have a greater number of future divisions.

Cell cycle

The sequence of events through which a cell grows, replicates its DNA, and divides.

Interphase

The period of the cell cycle between divisions, including G1, S, and G2 phases.

G1 phase

The cell-growth phase following mitosis and before DNA synthesis.

S phase

The phase of the cell cycle during which DNA is synthesized and replicated.

G2 phase

The phase following DNA synthesis and preceding mitosis.

M phase

The mitotic phase in which the cell divides.

Mitosis

The process by which one cell divides into two daughter cells; one of the most radiosensitive stages of the cell cycle.

Apoptosis

Programmed cell death.

Nucleus

The cell structure containing DNA; more radiosensitive than the cytoplasm.

Cytoplasm

The portion of the cell outside the nucleus; generally less radiosensitive than the nucleus.

DNA

Deoxyribonucleic acid; the most radiosensitive cellular macromolecule and a critical target for radiation damage.

RNA

Ribonucleic acid; a cellular macromolecule that is less radiosensitive than DNA.

Protein

A cellular macromolecule that is generally less radiosensitive than DNA and RNA.

Cellular macromolecule

Large molecule such as DNA, RNA, or protein that can be damaged by radiation.

LET

Linear energy transfer; the rate at which radiation deposits energy along the path of a charged particle.

Low-LET radiation

Radiation that deposits energy relatively sparsely along its path; X-rays and gamma rays are examples.

High-LET radiation

Radiation that deposits energy densely along its path; alpha particles and neutrons are examples.

RBE

Relative biological effectiveness; compares the biological effectiveness of different types of radiation for producing the same biological effect.

OER

Oxygen enhancement ratio; describes the increase in radiation effect caused by the presence of oxygen.

Oxygen effect

The enhancement of radiation-induced biological damage in the presence of oxygen.

Direct effect

Radiation directly ionizes or excites a critical cellular molecule such as DNA.

Indirect effect

Radiation interacts with another molecule, especially water, producing reactive products that damage critical cellular targets.

Radiolysis of water

The decomposition of water molecules caused by ionizing radiation.

Free radical

A highly reactive atom or molecule containing an unpaired electron.

Hydroxyl radical (OH•)

A highly reactive free radical produced during the radiolysis of water that can damage cellular molecules.

Hydrogen peroxide (H2O2)

A reactive product of water radiolysis that can contribute to cellular damage.

Ionization

The removal of an electron from an atom or molecule, producing an ion.

Excitation

The addition of energy to an atom or molecule without removing an electron.

Main-chain scission

The breaking of the main molecular chain caused by radiation damage.

Cross-linking

The joining of two molecules or parts of the same molecule as a result of radiation damage.

Point lesion

A small, localized area of molecular damage.

Point mutation

A change in the DNA sequence caused by damage to a small portion of the DNA.

Chromosome aberration

A structural or numerical change in a chromosome caused by radiation or other factors.

Dicentric chromosome

A chromosome containing two centromeres.

Ring chromosome

A chromosome whose broken ends join together to form a ring.

Reciprocal translocation

The exchange or rearrangement of chromosome segments between chromosomes.

Karyotype

A visual representation or map of an individual's chromosomes.

Dose-response relationship

The relationship between the amount of radiation dose and the resulting biological response.

Linear relationship

A dose-response relationship in which the response is directly proportional to dose.

Nonlinear relationship

A dose-response relationship in which the response is not directly proportional to dose.

Threshold

A dose level below which a specified biological response is not expected to occur.

Threshold dose

The minimum dose at which a particular biological effect is expected to occur.

Nonthreshold relationship

A dose-response relationship in which a biological effect is possible at any radiation dose.

Linear nonthreshold model

A model assuming that the probability of a biological effect increases linearly with dose and that there is no safe threshold.

Linear-quadratic relationship

A dose-response relationship containing both linear and quadratic components.

Sigmoid curve

An S-shaped dose-response curve.

Target theory

The theory that radiation produces biological damage when a critical target within the cell is hit; DNA is considered the critical target.

Critical target

The cellular structure whose damage is responsible for producing the biological effect; DNA is the major critical target.

Bystander effect

A radiation-induced biological effect occurring in cells that were not directly irradiated but are near irradiated cells.

Sister chromatid exchange

The exchange of genetic material between sister chromatids; can occur as a radiation-associated bystander effect.

Micronucleation

The formation of small, extra nuclei resulting from chromosome damage or chromosome fragments.

Cell transformation

A change in a cell that can alter its normal growth or behavior.

Gene expression

The process by which information in genes is used to produce functional cellular products.

Cell survival curve

A graph showing the relationship between radiation dose and the fraction of cells that survive.

Surviving fraction

The proportion of cells that remain capable of reproductive survival after radiation exposure.

Reproductive survival

The ability of a cell to continue dividing and produce viable daughter cells.

Shoulder

The initial portion of a cell-survival curve representing the cell's ability to tolerate or repair sublethal damage.

Sublethal damage

Radiation damage that can be repaired by the cell and does not immediately cause cell death.

High radiosensitivity

A characteristic of cells that are easily damaged or killed by radiation.

Highly radiosensitive cells

Lymphocytes, spermatogonia, erythroblasts, and intestinal crypt cells.

Intermediate radiosensitivity

Cells such as endothelial cells, osteoblasts, spermatids, and fibroblasts.

Low radiosensitivity

Cells such as muscle cells, nerve cells, and chondrocytes.

Lymphocytes

Highly radiosensitive blood cells.

Spermatogonia

Highly radiosensitive precursor cells involved in sperm production.

Erythroblasts

Immature red blood cell precursors that are highly radiosensitive.

Intestinal crypt cells

Rapidly dividing intestinal cells that are highly radiosensitive.

Endothelial cells

Cells lining blood vessels; considered to have intermediate radiosensitivity.

Osteoblasts

Cells responsible for forming bone; considered to have intermediate radiosensitivity.

Spermatids

Developing male germ cells with intermediate radiosensitivity.

Fibroblasts

Connective-tissue cells with intermediate radiosensitivity.

Muscle cells

Highly differentiated cells that are relatively radioresistant.

Nerve cells

Highly differentiated cells that are relatively radioresistant.

Chondrocytes

Cartilage cells that are relatively radioresistant.