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Glossary

Aldehyde: organic compound possessing an aldehyde group whose structure includes a carbon atom, bound to a hydrogen atom and attached by a double bond to an atom of oxygen. Several aldehydes are disinfecting agents, such as formaldehyde (formol).

Alpha helix: polypeptide chain which assumes a clockwise (right-handed) helical conformation and is stabilized by low-energy intrachain chain bonds called hydrogen bonds.

Amine (R - NH2): nitrogen-containing organic compound derived from ammonia (NH3) by replacement of its hydrogen atoms by one or more organic groups. Certain neurotransmitters have an amine function (dopamine, adrenaline).

Amyloid: a polymerized glycoprotein which resembles starch and which in certain diseases is deposited in the form of plaque-building fibrils (amyloid plaques) in various organs (spleen), including the central nervous system.

Antibody: defence protein produced by the cells (lymphocytes B) of the immune system of an animal, following interaction with a bacterium, virus or xenobiotic substance.

Apoptosis: genetically programmed cell death (suicide). Anomalies in apoptosis play a role in certain diseases, including degenerative brain diseases.

Ataxia: loss of control of the limbs due to damage to the nervous system.

Axon: long extension of a nerve cell which ensures the transmission of the nerve signal along the neurone.

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Beta-pleated sheet: chain of polypeptides arranged in parallel and forming a folded, accordion-like, highly stretched conformation.

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Central nervous system: the principal system that processes nervous information in vertebrates. It includes the brain, cerebellum and spinal cord.

Chaperone (chaperone protein): a protein which ensures the correct folding of another protein thus enabling it to fulfil its function, as a catalyst, for instance.

Chromosome: structure formed by a DNA molecule and associated proteins (histones... ) which carries the hereditary information of an organism possessing a nucleus . The number of chromosomes is characteristic of a given species.

Codon: sequence of adjacent nucleotides in a nucleic acid (DNA or messenger RNA) which constitutes the code that instructs the incorporation of a specific amino acid in a protein chain being formed .

Conformation: three-dimensional shape of a macromolecule.

Cytoplasm: contents of a cell delimited by a plasma membrane.

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DNA (deoxyribonucleic acid): high molecular weight nucleic acid containing deoxyribose as sugar, which serves as the genetic information carrier (genome) of living organisms. In eukaryotic cells, DNA is found in the nucleus.

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Electrophoresis: technique of fractionating proteins based on the ability of electrically charged molecules to migrate in an electric field.

Encephalopathy: a disease affecting the encephalon, part of the central nervous system comprising the brain, the cerebellum and the medulla oblongata.

Epidemiological: pertaining to epidemiology, the field of medicine concerned with the development of a disease in a large number of individuals in a given region.

Epizootic: an outbreak of disease affecting an unusually large number of animals throughout a given region.

Eukaryote: living organism comprising one or more cells whose genetic material (DNA) is concentrated in the nucleus . Animals, plants, fungi and yeasts are eukaryotes.

Eukaryotic cells: organisms comprising one cell (yeasts) or several cells (animals, plants, fungi) whose genetic material (DNA) is stored in the nucleus.

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Gene: unit of heredity corresponding to a region of DNA which controls a particular character. A gene governs the synthesis of a single protein or of a single RNA and thus conditions the transmission or manifestation of a given hereditary character.

Genetic: inherited. Genetics is the science of the heredity of living organisms.

Genetic engineering: the set of techniques used to alter the genetic material of a cell or living organism.

Genome: the sum total of the genetic material specific to each species of organism.

Genotype: genetic constitution of a cell or individual organism.

Glial cells: cells that supply nutrients to the neurones and which in the central nervous system include astrocytes and oligodendrocytes.

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Heterozygote: an individual possessing different alleles of a gene for a given character.

Heterozygosity: the state of possessing different alleles of a gene at a given locus.

Histological: pertaining to histology, the science of the tissues of living organisms.

Homogenate: tissue that has been homogenized.

Homozygote: diploid cell (containing two copies of each gene) or an organism with two identical alleles (alternative forms of the same gene) of a given gene. This contrasts with a heterozygote, in which the two alleles are not identical.

Horizontal transmission: transmission between generally adult individuals (cf vertical transmission : from mother to child).

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Iatrogenic: resulting from a medical act or medication.

Immunohistochemistry: technique of using labelled antibodies to label a specific protein in a tissue section (examined under the microscope).

Ionizing radiation: radiation (X-rays, gamma rays, etc.) whose energy is enough to ionize, that is to strip electrons from the outer layers of atoms or molecules.

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Kuru: neurodegenerative human disease of the spongiform encephalopathy type, which for over a century affected solely the Fore tribe in Papua New Guinea (Oceania).

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Lysosomes: small organelles in eukaryotic cells that are rich in hydrolytic enzymes (peptidases, amidases...).

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Macromolecule: molecule of high molecular weight (above several thousand Daltons) . Many macromolecules are organic in nature and are essential to life. Among biological macromolecules are proteins (structural proteins, transport proteins, enzymes...), polysaccharides (complex sugars), nucleic acids (DNA and RNA).

Macrophages: white cells that do not circulate in the blood or lymphatic system and play a vital role in our defence systems against airborne chemical (dust) or biological (bacteria, viruses...) agents.

Membrane: double layer of lipoprotein macromolecules (phospholipids containing unsaturated fatty acids associated with proteins) which envelop prokaryotic cells (bacteria, algae...). In eukaryotic cells, biological membranes separate the cell from the outside world (plasma membrane) and also delineate the different organelles (nucleus, mitochondria) within the cell's cytoplasm.

Metabolic: pertaining to metabolism, which in living organisms is the sum of all chemical transformations catalyzed by enzymes and allowing the transformation of biological molecules.

Mineral base: inorganic molecule able to fix a proton (H+). Sodium hydroxide (NaOH) and potassium hydroxide (KOH) are strong, highly corrosive bases which attack many materials and destroy living matter.

Mitochondria: small organelles in the cytoplasm which are the cell's power sources.

Mutation: change in a gene that can be transmitted to other generations, resulting in a hereditary change.

Myoclonia: involuntary contractions of the muscles.

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Neurone: nerve cell comprising a cell body containing the nucleus, an axon (long membrane outgrowth) and nerve endings : the dendrites, which at the synapse ensure axonal communication, i.e. transmission of the nerve signal.

Neurotransmitters: chemical messengers released by the nerve cells subject to an electrical influx (action potential) which is created by the movement of ions across the plasma membrane of the nerve cell. These chemical molecules act as messengers to transmit the messages produced by the nerve cells.

NMR (nuclear magnetic resonance): spectral technique based on the capacity of atomic nuclei for resonant absorption of electromagnetic radiation. NMR can be used to determine the three-dimensional structure of small water-soluble proteins.

Nonioizing radiation: radiation (ultraviolet, infrared, visible light) whose energy is insufficient to ionize atoms or molecules.

Nucleation: acting as a nucleus for, in a process of formation (of crystals, for example).

Nucleic acids: biological macromolecules formed by the combination of simpler nitrogen-containing molecules - nucleotides, elementary units containing pyrimidine and purine bases, a sugar of five carbon atoms (pentose) and a phosphate. These molecules are the physical support of the genetic information, ie the basis of life.

Nucleus: in eukaryotic cells (animals, plants, yeasts...), large organelle containing the chromatin formed from DNA and nuclear proteins.

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Oraganelle: well-characterized element isolated by a membrane within the cytoplasm of a eukaryotic cell.

Ozone: trioxygen (O3) gas which is extremely oxidizing and toxic and is used as a bactericide (disinfection of water...).

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Peptide: molecule of moderate size formed by the association of amino acids linked together by peptide bonds. Peptides form proteins.

Polypeptide: small macromolecule formed by the chains of several peptides themselves comprising amino acids linked together by peptide bonds.

Precautionary prinoiple: the absence of certainty, in view of current scientific and technical knowledge, should not delay the adoption of preventive measures.

Primary structure: sequence of simple units in a polymer,for example, that of amino acids in a peptide chain or a protein.

Prion: protein found in animals, but also yeasts, which can exist in two forms : one normal, the other altered.

Prokaryotic cells: living organisms of relatively simple structure characterized by a cytoplasm containing dispersed DNA not delimited in a nucleus. Bacteria and blue algae are prokaryotes.

Protease: proteolytic enzyme which degrades proteins by hydrolyzing, sometimes very selectively, some of their peptide bonds.

Protein: macromolecule generally of high molecular weight which comprises several polypeptide chains, each of which has a characteristic sequence of amino acids. Certain proteins have a structural role in cells (biomembrane, cytoskeleton...), others play a part in transport (haemoglobin...), catalysis (enzymes...) or communication (hormones, cytokines...).

Proteolysis: degradation of a protein, generally by hydrolysis of at least one of its peptide bonds.

Pruritus: itching of the skin due to cutaneous or systemic disease.

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RNA (ribonucleic acid): nucleic acid, generally of medium molecular weight, based on ribonucleotides whose sugar is ribose. Ribonucleic acids are mainly found in the cytoplasm of eukaryotic cells, in the ribosomes, which synthesize proteins. RNAs decode the genetic information carried by the DNA for subsequent synthesis of proteins.

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Scarification: superficial incision in the skin.

Scrapie: a transmissible nervous disease in sheep and goats with an incubation period of between two and four years. Known in Europe since the 18th century.

Secondary structure: motif of regular local folding of a polymeric molecule. In proteins, there are two types of secondary structure: alpha helices and beta-pleated sheets.

Sodium hydroxide: strong, extremely corrosive mineral base.

Sodium hypochlorite (NaOCl): sodium salt of hypochlorous acid (HOCI). Bleach contains mostly sodium hypochlorite whose oxidizing properties make it a powerful disinfectant.

Spectroscopy: technique for measuring the absorption of radiation of various wavelengths (IR, visible, UV).

Spongiosis: spongelike appearance of nerve tissue due to the presence of vacuoles in the neurones.

Sporadic (disease): disease that affects a limited number of unrelated subjects.

Strain: all individuals (bacteria, etc.) from the same colony of microorganisms. A strain of prions results from the transmission of a prion disease to several successive hosts.

Syngeneic: individuals or tissues that have an identical genetic makeup, following successive controlled crosses.

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Tertiary structure: three-dimensional shape of a macromolecule. In proteins, their tertiary structure corresponds to the conformation of the polypeptide chains.

Trace element: mineral element essential to living organisms in very small amounts and whose lack results in severe nutritional deficiencies.

Transgenic: plants or animals in which one or more genes of another cell or organism have been stably incorporated experimentally and which can be transmitted to subsequent
generations.

Transmissible agent: element which is responsible for a disease.

TSSEs (transmissible subacute spongiform encephalopathies): group of diseases affecting the central nervous system. They are characterized by the progressive destruction of the neurones of
certain zones of the encephalon, following the accumulation of a pathological protein, PrPres, thus giving the nervous tissue a spongelike appearance.

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Unconventional transmissible agent (UTA): name of the biological agent responsible for transmissible spongiform encephalopathies.

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Vacuole: cellular storage organelle.

Virino: very small infectious particle composed of genetic material (DNA,RNA) surrounded by a lipoprotein envelope belonging to the host.

Virus: particle consisting of a nucleic acid (based on DNA or RNA, as in retroviruses) surrounded by a protein envelope and which can reproduce inside a host cell.

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