Unit 3: Overview of Cellular & Molecular Radiation Biology

A set of vocabulary-style flashcards covering key terms and definitions from the lecture notes on cellular and molecular radiation biology.

Cell membrane

The phospholipid bilayer surrounding the cell that provides structure, protection, and selective permeability.

Cytoplasm

The gel-like interior between the membrane and nucleus containing organelles and site of many cellular activities.

Nucleus

The membrane-bound organelle containing DNA and regulating cellular activities and division.

Nucleolus

Structure within the nucleus that synthesizes ribosomal RNA and assembles ribosomes.

Endoplasmic reticulum

Network of sac-like structures in the cytoplasm; rough ER has ribosomes and makes proteins, smooth ER synthesizes lipids and transports molecules.

Golgi apparatus

Organelle that processes, packages, and transports proteins and lipids to their destinations, including secretion.

Mitochondria

Double-membrane organelles that generate most of the cell’s energy (ATP) through oxidative metabolism.

Lysosomes

Single-membrane organelles containing digestive enzymes that break down molecules and destroy pathogens; rupture can damage the cell.

Ribosomes

Small RNA-protein particles that synthesize proteins; can be free in cytoplasm or attached to the endoplasmic reticulum.

Centrosomes

Structure near the nucleus containing a pair of centrioles; organizes the mitotic spindle during cell division.

Chromosome

DNA-protein structures carrying genetic information; humans have 46 total (23 pairs) in somatic cells.

Gene

Specific DNA segment that encodes a functional product (protein or RNA) and determines inherited traits.

DNA

Deoxyribonucleic acid, the double-helix molecule that carries genetic information for replication and protein synthesis.

RNA

Ribonucleic acid; single-stranded molecule involved in transmitting genetic information and protein synthesis; includes mRNA and tRNA.

mRNA

Messenger RNA; transcribes DNA information and directs protein synthesis in the cytoplasm.

tRNA

Transfer RNA; brings specific amino acids to the ribosome during protein synthesis.

Protein

Large molecules made of amino acids with structural, enzymatic, regulatory, and immune functions.

Carbohydrate

Organic compounds providing quick energy; glucose is the primary energy source; ~1% of cell mass.

Lipid

Fatty substances that store energy, insulate, cushion organs, and support cells; ~2% of cell mass.

Water

Major component of cells and the body; solvent for reactions and involved in temperature regulation and transport.

Glucose

Primary simple sugar used by cells as a quick energy source.

Ionizing radiation

High-energy radiation capable of removing electrons from atoms, leading to chemical and biological damage.

LET (Linear Energy Transfer)

Average energy deposited per unit track length as radiation travels through tissue; higher LET means more damage.

Low-LET radiation

X-rays and gamma rays; electromagnetic, highly penetrating with low mass/charge; damage mainly via indirect action.

High-LET radiation

Alpha particles, protons, neutrons; particulate with substantial mass/charge; dense ionization and greater localized damage.

Beta particle

High-speed electrons with moderate penetration and intermediate LET.

RBE (Relative Biologic Effectiveness)

Ratio of doses of reference and test radiations needed to produce the same biological effect; higher LET often increases RBE.

Oxygen Enhancement Ratio (OER)

Ratio of dose without oxygen to dose with normal oxygen to achieve the same biological effect; oxygen increases radiosensitivity.

Somatic cell

Body cells; radiation effects in these cells affect the individual, not inheritance.

Germ cell

Reproductive cells (sperm and ova); radiation damage can be inherited as genetic mutations.

Direct action

Radiation directly ionizes essential cellular macromolecules (DNA/RNA/proteins) causing damage; more common with high-LET radiation.

Indirect action

Radiation first interacts with water to create free radicals, which then damage cellular molecules; predominant for low-LET radiation.

Free radical

Highly reactive atoms or molecules formed by radiolysis with unpaired electrons.

Radiolysis

Dissociation of water molecules into free radicals due to ionizing radiation.

Single-strand break

Break in one strand of DNA; can lead to mutations and is often repairable.

Double-strand break

Break in both DNA strands; more difficult to repair and more lethal to cells.

Chromosome aberration

Structural abnormality of chromosomes after radiation due to misrejoining of fragments.

Instant death

Cell death from extremely high radiation doses (roughly 1000 Gy) in a short time.

Reproductive death

Cell cannot reproduce after exposure, even if it remains alive (typically 1-10 Gy).

Apoptosis

Programmed cell death; can occur spontaneously or be induced by radiation; occurs during interphase.

Mitotic death

Cell dies after one or two divisions due to radiation-induced genetic damage.

Mitotic delay

Delay in cell division after radiation; even small doses (as low as ~10 cGy) can cause a delay.

Radiosensitivity

Relative susceptibility of cells and tissues to radiation damage; varies with maturation, differentiation, and division rate.

Epithelial tissue

Outer coverings and glandular tissue; highly radiosensitive due to rapid regeneration.

Muscle tissue

Tissue of muscle; mature, differentiated, and slowly dividing cells are less radiosensitive.

Nervous tissue

Brain and spinal cord; highly specialized, rarely divide, and are relatively radioresistant.

Spermatogonia

Immature germ cells in testes; highly radiosensitive; small doses can depress sperm or cause mutations.

Ova

Ovarian eggs; immature ova are highly radiosensitive; doses determine risks for sterility and genetic damage.

LD50/30

The lethal dose that would kill 50% of a population within 30 days after exposure.

LD50/60

The lethal dose that would kill 50% of a population within 60 days after exposure (humans).