Glossary T-Z

T Cells: One of the two major types of lymphocytes (white blood cells) There are two types of T-cells - "helper" T-cells and "killer" T-cells.

Thymidine: One of the four basic nucleotides that comprise DNA.

Tobacco mosaic disease: The first recognized viral disease, tobacco mosaic disease is caused by the tobacco mosaic virus (TMV). It attacks tobbaco leaves, causing a mosaic-like pattern of discolorations in the plant.

Transcriptase: RNA polymerase; an enzyme that catalyzes the synthesis of RNA with DNA serving as a template, also known as RNA transcriptase.

Transmission: The transfer of a disease from one person to another.

Trichloroacetic acid: CCI3COOH, Toxic, deliquescent, colorless crystals with a pungent aroma, used as a chemical intermediate and library reagent, and in medicine, pharmacy, and herbicides.

Triglyceride: The most important of three groups of neutral fats; the basic unit consists of a molecule of glycerol in ester bond with three molecules of fatty acid; it serves as the major storage form of fatty acids and is practically the exclusive

constituent of adipose tissue.

Urea: Chief end product of mammalian protein metabolism, formed in the liver from amino acids and compounds of ammonia; the chief nitrogenous compound of urine; an average person, in steady state of consuming average amounts of dietary protein, excretes about 30 grams of urea per day.

Vaccine: A preparation of dead or live attenuated, viruses or bacteria used to prevent infectious diseases by inducing active immunity.

Very Low Density Lipoprotein: A class of low density conjugated proteins consisting of a protein and a lipid.

Vesicles: Small "bubbles" of lipid within a cell, used for the transport of materials within the cell and between the cell membrane and the outside environment.

Viral particle: The new viruses reproduced inside of a cell.

Viral proteins: Among the most important characteristics of a virus is the nature of the proteins which make up its capsid, envelope, and spikes. Proteins determine the infective properties of the virus.

Viroid: Viroids are composed of

nothing more than a single, circular strand of genetic material, and cause disease in plant cells. Replicating in the nuclei of plant cells, they often cause striking diseases in their host plants. Lacking even a protective shell of protein, viroids do not even spread easily from one cell or plant to another.

Virion: A complete virus particle.

Virus: A sub-microscopic life form that uses host cells - bacteria, plant cells, or even human body cells to reproduce itself. A virus normally consists of a small amount of genetic material (which it uses to reproduce itself) and a protective coat. Viruses are very small - most human viruses are less than 150 nanometers in diameter. (A nanometer is one billionth of a meter).

Virusoid: An extremely simple virus, normally consisting of little more than a single circular strand of genetic material. Virusoids "infect" other viruses, using the replication processes of the host virus to replicate themselves instead.

White blood cell: The cells which form the basic constituents of the human immune system.

Yellow fever: A RNA virus that multiplies in the cytoplasm of cells; transmitted by arthropods.