Radiation Biology Educator Guide Glossary Adenine (A) A nitrogenous base which binds to thymine to help build the DNA structure. Allele Alternative form of genetic coding at a specific locus (position) on the chromosome; a single allele for each locus is inherited from each parent (e.g., at a locus for eye color the allele might result in blue or brown eyes). Alpha radiation (Alpha ray, alpha particle, particle) An alpha ray is a particle emitted from the nucleus of an atom and contains two protons and two neutrons, and, so, has a positive charge (+2). It is identical to the nucleus of a helium atom stripped of its electrons. Alpha particles have the least penetrating power of all radiation because they are emitted with relatively slow velocity. Amino acid Any of a class of 20 molecules that are used to synthesize proteins in living things. The sequence of amino acids in a protein and hence protein function is determined by the genetic code. Apoptosis Programmed cell death, the body's normal method of disposing of damaged, unwanted or unneeded cells. Atom A particle of matter indivisible by chemical means. An atom has a nucleus made up of protons and neutrons and a surrounding 'cloud' of electrons. The atom is neutrally charged, as the number of protons and electrons is identical. It is the fundamental building block of the elements, which consist of atoms whose nuclei contain increasing numbers of protons and neutrons. Autosomal gene An autosome is a non-sex chromosome. It is an ordinary paired chromosome that is the same in both sexes of a species. For example, in humans, there are 22 pairs of autosomes. The X and Y chromosomes are not autosomal. Non-autosomal chromosomes are usually referred to as sex chromosomes, allosomes or heterosomes. Base One of five nucleotides (adenine, thymine, guanine, cytosine, uracil) that form DNA and RNA molecules. Base pair (bp) Two nitrogenous bases (adenine and thymine, and guanine and cytosine in DNA) held together by weak bonds. Two complementary strands of DNA are held together in the shape of a double helix by the bonds between base pairs. Base sequence The order of nucleotide bases in a DNA molecule; determines structure of proteins encoded by that DNA. Becquerel (Bq) The SI unit for measuring radioactivity. If a quantity of radioactive material undergoes one atom decay per second, it has an activity of one Bq. Comparable common unit is a curie. Named for Antoine Henri Becquerel who shared a Nobel Prize with Marie Curie for their work in discovering radioactivity. Beta radiation (Beta ray, beta particle, particle) A beta-ray is an electron emitted from the nucleus of an atom following the decay of a neutron into a proton. Beta rays are more penetrating than alpha rays, move at a very high-speed and are deflected considerably by a magnetic field in a direction that indicates a negative charge. Cancer Diseases in which abnormal cells divide and grow unchecked. Cancer can spread from its original site to other parts of the body and can be fatal. Cell The basic unit of any living organism that carries on the biochemical processes of life. Centromere A specialized chromosome region to which spindle fibers attach during cell division. Chromosome The self-replicating genetic structure of cells containing the cellular DNA that bears in its nucleotide sequence the linear array of genes. In prokaryotes, chromosomal DNA is circular and the entire genome is carried on one chromosome. Eukaryotic genomes consist of a number of chromosomes whose DNA is associated with different kinds of proteins. Comparative genomics The study of human genetics by comparisons with model organisms such as mice, the fruit fly and the bacterium E. coli. Congenital Any trait present at birth, whether the result of a genetic or nongenetic factor. Cosmic rays Cosmic rays are charged particles moving at nearly the speed of light from beyond the Earth. Primary cosmic rays consist mostly of protons (nuclei of hydrogen atoms), some alpha particles (helium nuclei), and lesser amounts of nuclei of carbon, nitrogen, oxygen and heavier atoms. Cosmic rays collide with nuclei in the upper atmosphere, producing secondary cosmic rays of protons, neutrons, mesons, electrons, and gamma rays of high energy. In turn these collide with nuclei lower in the atmosphere to produce more particles. Coulomb The SI unit to define the amount of electrical charge transferred in one second by a steady current of one ampere. It can also be defined in terms of the ability of radiation to ionize air, where the electric charges created can be collected and measured. Comparable common unit is a roentgen. Named for Charles Augustin de Coulomb, a French physicist who developed electrical and mechanical theories. Curie (Ci) The basic unit used to describe the intensity of radioactivity in a sample of material. One curie equals 37 billion (3.7 x 10 10) disintegrations per second or approximately the radioactivity of one gram of the radium isotope 226Ra. The comparable SI unit-the Becquerel - is more commonly used today. Named after Marie Curie, a pioneer in the early field of radioactivity. Cytosine (C) A nitrogenous base, one member of the base pair GC (guanine and cytosine) in DNA. Deletion A loss of part of the DNA from a chromosome; can lead to a disease or abnormality. Diploid A full set of genetic material consisting of paired chromosomes, one from each parental set. Most animal cells except the gametes have a diploid set of chromosomes. The diploid human genome has 46 chromosomes. DNA (deoxyribonucleic acid) The molecule that encodes genetic information. DNA is a double-stranded molecule held together by weak bonds between base pairs of nucleotides. The four nucleotides in DNA contain the bases adenine (A), guanine (G), cytosine (C) and thymine (T). In nature, base pairs form only between A and T and between G and C; thus the base sequence of each single strand can be deduced from that of its partner. DNA sequence The relative order of base pairs, whether in a DNA fragment, gene, chromosome or an entire genome. Dominant An allele that is almost always expressed, even if only one copy is present. Double helix The twisted-ladder shape that two linear strands of DNA assume when complementary nucleotides on opposing strands bond together. Electromagnetic radiation Electromagnetic radiation is produced by the oscillatory motion of charged particles, for example by electrons moving in an antenna. The electromagnetic (EM) spectrum is made up of a range of EM radiation with ever diminishing wavelength and ever increasing energy: radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X rays and gamma radiation. EM radiation can also be described in terms of massless particles called photons that travel in a wave-like pattern at the speed of light. Electrophoresis A method of separating large molecules (such as DNA fragments or proteins) from a mixture of similar molecules. An electric current is passed through a medium containing the mixture and each kind of molecule travels through the medium at a different rate, depending on its electrical charge and size. Agarose and acrylamide gels are the media commonly used for electrophoresis of proteins and nucleic acids. Enzyme A protein that acts as a catalyst, speeding the rate at which a biochemical reaction proceeds but not altering the direction or nature of the reaction. Escherichia coli Common bacterium that has been studied intensively by geneticists because of its small genome size, normal lack of pathogenicity and ease of growth in the laboratory. Eukaryote Cell or organism with membrane-bound, structurally discrete nucleus and other well-developed subcellular compartments. Eukaryotes include all organisms except viruses, bacteria and blue-green algae. Filial generation (F1, F2) Each generation of offspring in a breeding program, designated F1, F2, etc. Flow cytometry Analysis of biological material by detection of the light-absorbing or fluorescing properties of cells or subcellular fractions (i.e., chromosomes) passing in a narrow stream through a laser beam. An absorbance or fluorescence profile of the sample is produced. Automated sorting devices, used to fractionate samples, sort successive droplets of the analyzed stream into different fractions depending on the fluorescence emitted by each droplet. Fluorescence in situ hybridization (FISH) A physical mapping approach that uses fluorescein tags to detect hybridization of probes with metaphase chromosomes and with the less-condensed somatic interphase chromatin. Full gene sequence The complete order of bases in a gene. This order determines which protein a gene will produce. Functional genomics The study of genes, their resulting proteins and the role played by the proteins in the body's biochemical processes. Gamete Mature male or female reproductive cell (sperm or ovum) with a haploid set of chromosomes (23 for humans). Gamma radiation (Gamma ray, gamma particle, particle) Gamma rays are electromagnetic waves or photons emitted from the nucleus of an unstable (radioactive) atom. They have no mass, no charge. Gamma rays have very great penetrating power and are not affected at all by a magnetic field. They move at the speed of light and have a very short wavelength. Gel electrophoresis A method of separating large molecules (such as DNA fragments or proteins) from a mixture of similar molecules. An electric current is passed through a medium containing the mixture, and each kind of molecule travels through the medium at a different rate, depending on its electrical charge and size. Agarose and acrylamide gels are the media commonly used for electrophoresis of proteins and nucleic acids. Gene The fundamental physical and functional unit of heredity. A gene is an ordered sequence of nucleotides located in a particular position on a particular chromosome that encodes a specific functional product (i.e., a protein or RNA molecule). Gene amplification Repeated copying of a piece of DNA; a characteristic of tumor cells. Gene chip technology Development of cDNA (complementary DNA) microarrays from a large number of genes. Used to monitor and measure changes in gene expression for each gene represented on the chip. Gene expression The process by which a gene's coded information is converted into the structures present and operating in the cell. Expressed genes include those that are transcribed into mRNA and then translated into protein and those that are transcribed into RNA but not translated into protein (e.g., transfer and ribosomal RNAs). Gene mapping Determination of the relative positions of genes on a DNA molecule (chromosome or plasmid) and of the distance, in linkage units or physical units, between them. Gene pool All the variations of genes in a species. Genetic code The sequence of nucleotides, coded in triplets (codons) along the mRNA, which determines the sequence of amino acids in protein synthesis. A gene's DNA sequence can be used to predict the mRNA sequence and the genetic code can in turn be used to predict the amino acid sequence. Genetics The study of inheritance patterns of specific traits. Genome All the genetic material in the chromosomes of a particular organism; its size is generally given as its total number of base pairs. Genomics The study of genes and their function. Genotype The genetic constitution of an organism, as distinguished from its physical appearance (its phenotype). Gray (Gy) The SI unit for the energy absorbed from ionizing radiation, equal to one joule per kilogram. Comparable common unit is a rad. Named after Louis Harold Gray, a British physicist who invented the field of radiobiology. Guanine (G) A nitrogenous base, one member of the base pair GC (guanine and cytosine) in DNA. Half-life of an element The rate of disintegration of a radioactive substance is commonly referred to as its half-life, which is the time required for one half of a given quantity of the substance to decay. Depending on the element, a half-life can be as short as a fraction of a second or as long as several billion years. Haploid A single set of chromosomes (half the full set of genetic material) present in the egg and sperm cells of animals and in the egg and pollen cells of plants. Human beings have 23 chromosomes in their reproductive cells. Homolog A member of a chromosome pair in diploid organisms or a gene that has the same origin and functions in two or more species. Hybrid The offspring of genetically different parents. In situ hybridization Use of a DNA or RNA probe to detect the presence of the complementary DNA sequence in cloned bacterial or cultured eukaryotic cells. Independent assortment During meiosis each of the two copies of a gene is distributed to the germ cells independently of the distribution of other genes. Inherit In genetics, to receive genetic material from parents through biological processes. Interphase The period in the cell cycle when DNA is replicated in the nucleus; it is followed by mitosis. Ionizing radiation Ionizing radiation is radiation with enough energy, such that during an interaction with an atom, it can remove tightly bound electrons from their orbits, causing the atom to become charged or ionized. Examples are X-rays, gamma rays, electrons and neutrons. Isoenzyme An enzyme performing the same function as another enzyme but having a different set of amino acids. The two enzymes may function at different speeds. Isotope An isotope is a different form of a given element that has the same atomic number (same number of protons in the nucleus) but a different atomic weight (different number of neutrons in the nucleus). Uranium-238 and uranium-235 are isotopes of uranium. Karyotype A photomicrograph of an individual's chromosomes arranged in a standard format showing the number, size and shape of each chromosome type; used in low-resolution physical mapping to correlate gross chromosomal abnormalities with the characteristics of specific diseases. Knockout Deactivation of specific genes; used in laboratory organisms to study gene function. Meiosis The process of two consecutive cell divisions in the diploid progenitors of sex cells. Meiosis results in four rather than two daughter cells, each with a haploid set of chromosomes. Mendelian inheritance One method in which genetic traits are passed from parents to offspring. Named for Gregor Mendel, who first studied and recognized the existence of genes and this method of inheritance. Messenger RNA (mRNA) RNA that serves as a template for protein synthesis. Metaphase A stage in mitosis or meiosis during which the chromosomes are aligned along the equatorial plane of the cell. Microarray Sets of miniaturized chemical reaction areas on solid surfaces that may be used to test DNA fragments, antibodies or proteins. Mitochondrial DNA The genetic material found in mitochondria, the organelles that generate energy for the cell. Not inherited in the same fashion as nucleic DNA. Mitosis The process of nuclear division in cells that produces daughter cells that are genetically identical to each other and to the parent cell. Model organisms A laboratory animal or other organism useful for research. Modeling The use of statistical analysis, computer analysis or model organisms to predict outcomes of research. Mutagen An agent that causes a permanent genetic change in a cell; does not include changes occurring during normal genetic recombination. Mutagenicity The capacity of a chemical or physical agent to cause permanent genetic alterations. Mutation Any heritable change in DNA sequence. Neutron A neutron is an uncharged elementary particle of slightly greater mass than the proton. The stable isotopes of all elements except hydrogen and helium contain a number of neutrons equal to or greater than the number of protons. They are normally contained in the nucleus of all atoms and may be removed by various interactions or processes like collision and fission. Nitrogenous base A nitrogen-containing molecule having the chemical properties of a base. DNA contains the nitrogenous bases adenine (A), guanine (G), cytosine (C) and thymine (T). Non-ionizing radiation Non-ionizing radiation is radiation without enough energy to remove tightly bound electrons from their orbits around atoms. Examples are microwaves and visible light. Northern blot A gel-based laboratory procedure that locates mRNA sequences on a gel that is complementary to a piece of DNA used as a probe. Nucleic acid A large molecule composed of nucleotide subunits. Nucleotide A subunit of DNA or RNA consisting of a nitrogenous base (adenine, guanine, thymine or cytosine in DNA; adenine, guanine, uracil or cytosine in RNA), a phosphate molecule and a sugar molecule (deoxyribose in DNA and ribose in RNA). Thousands of nucleotides are linked to form a DNA or RNA molecule. Nucleus The cellular organelle in eukaryotes that contains most of the genetic material. Peptide Two or more amino acids joined by a bond called a "peptide bond." Phenotype The physical characteristics of an organism or the presence of a disease that may or may not be genetic. Photon A photon is a discrete quantity of electromagnetic energy having momentum but no mass or electrical charge. Polymerase chain reaction (PCR) A method for amplifying a DNA base sequence using a heat-stable polymerase and two 20-base primers, one complementary to the (+) strand at one end of the sequence to be amplified and one complementary to the (-) strand at the other end. Because the newly synthesized DNA strands can subsequently serve as additional templates for the same primer sequences, successive rounds of primer annealing, strand elongation and dissociation produce rapid and highly specific amplification of the desired sequence. PCR also can be used to detect the existence of the defined sequence in a DNA sample. Population genetics The study of variation in genes among a group of individuals. Probe Single-stranded DNA or RNA molecules of specific base sequence, labeled either radioactively or immunologically, which are used to detect the complementary base sequence by hybridization. Prokaryote Cell or organism lacking a membrane-bound, structurally discrete nucleus and other subcellular compartments. Bacteria are examples of prokaryotes. Protein A large molecule composed of one or more chains of amino acids in a specific order; the order is determined by the base sequence of nucleotides in the gene that codes for the protein. Proteins are required for the structure, function and regulation of the body's cells, tissues and organs; each protein has unique functions. Examples are hormones, enzymes and antibodies. Proteome Proteins expressed by a cell or organ at a particular time and under specific conditions. Proteomics The study of the full set of proteins encoded by a genome. Proton A proton is an elementary particle that makes up the nucleus an atom. It has a single positive electrical charge. The positive charge of the nucleus of any atom is due to its protons. Every atomic nucleus contains one or more protons; the number of protons, called the atomic number, is different for every element. Purine A nitrogen-containing, double-ring, basic compound that occurs in nucleic acids. The purines in DNA and RNA are adenine and guanine. Pyrimidine A nitrogen-containing, single-ring, basic compound that occurs in nucleic acids. The pyrimidines in DNA are cytosine and thymine; in RNA, cytosine and uracil. Rad Radiation Absorbed Dose. The basic unit of an absorbed dose of ionizing radiation. One rad is equal to the absorption of 100 ergs of radiation energy per gram of matter. The comparable SI unit is a Gray (Gy). Radiation Radiation is energy in transit in the form of high-speed particles and electromagnetic waves. The radiation produced during radioactivity is predominantly of three types, designated as alpha, beta and gamma rays or particles. These types differ in velocity, in the way in which they are affected by a magnetic field, and in their ability to penetrate or pass through matter. Radioactive material Radioactive material is any material that contains radioactive atoms. Radioactivity Radioactivity is the spontaneous transformation of an unstable atom and often results in the emission of radiation. This process is referred to as a transformation, decay or a disintegration of an atom. Recessive gene A gene that will be expressed only if there are two identical copies or, for a male, if one copy is present on the X chromosome. Rem (Roentgen equivalent in man) A unit to describe the equivalent dose in a particular radiation type. It is the product of absorbed dose in roentgens and the weighting factor for a radiation type. The use of rem is discouraged in favor of the comparable SI unit Sievert (Sv), which is equal to 100 rem. Ribose The five-carbon sugar that serves as a component of RNA. Ribosomal RNA (rRNA) A class of RNA found in the ribosomes of cells. Ribosomes Small cellular components composed of specialized ribosomal RNA and protein; site of protein synthesis. RNA (Ribonucleic acid) A chemical found in the nucleus and cytoplasm of cells; it plays an important role in protein synthesis and other chemical activities of the cell. The structure of RNA is similar to that of DNA. There are several classes of RNA molecules, including messenger RNA, transfer RNA, ribosomal RNA and other small RNAs, each serving a different purpose. Roentgen (R) A unit of radiation exposure equal to the quantity of ionizing radiation that will produce one electrostatic unit of electricity in one cubic centimeter of dry air at 0°C and standard atmospheric pressure. The comparable SI unit is a Coulomb. Named after the German physicist, Wilhelm Roentgen. Sequencing Determination of the order of nucleotides (base sequences) in a DNA or RNA molecule or the order of amino acids in a protein. Sievert (Sv) The SI unit used to measure dose equivalent, which defines the biological rather than the physical effects of radiation. Dose equivalent is numerically equal to the dose in Gray multiplied by a quality factor (Q) for a particular radiation type. Comparable common unit is a rem, which is disappearing from usage. Named after Rolf Maximilian Sievert, a Swedish medical physicist who conducted research on the biological effects of radiation. Somatic cell Any cell in the body except gametes and their precursors. Systéme Internationale d'Unités (SI) units The international system of units (SI) is the system currently used in radiation biology. It is derived from the meter-kilogram-second (MKS) system where length is measured in meters, time in seconds and mass in kilograms. Telomere The end of a chromosome. This specialized structure is involved in the replication and stability of linear DNA molecules. Thymine (T) A nitrogenous base, one member of the base pair AT (adenine-thymine). Transcription The synthesis of an RNA copy from a sequence of DNA (a gene); the first step in gene expression. Translation The process in which the genetic code carried by mRNA directs the synthesis of proteins from amino acids. Ultraviolet light Electromagnetic radiation at wavelengths shorter than the violet end of visible light; the atmosphere of the Earth effectively blocks the transmission of most ultraviolet light. Uracil A nitrogenous base normally found in RNA but not DNA; uracil is capable of forming a base pair with adenine. Visible light Electromagnetic radiation at wavelengths that the human eye can see. We perceive this radiation as colors ranging from red (longer wavelengths; ~ 700 nanometers) to violet (shorter wavelengths; ~ 400 nanometers). Wave-particle duality The principle of quantum mechanics which implies that light (and indeed all other subatomic particles) sometimes acts like a wave and sometimes acts like a particle, depending on the experiment you are performing. For instance, low frequency electromagnetic radiation tends to act more like a wave than a particle; high frequency electromagnetic radiation tends to act more like a particle than a wave. Western blot A technique used to identify and locate proteins based on their ability to bind to specific antibodies. X-rays Electromagnetic radiation of very short wavelength and very high energy; X-rays have shorter wavelengths than ultraviolet light but longer wavelengths than gamma rays.
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