Adenine: A white, crystalline derivative; one of the four basic nucleotides that comprise DNA.
Adipose tissue: A type of connective tissue specialized for lipid (fat) storage.
Aggregate cost: The sum total of costs.
AIDS: Auto-immune deficiency syndrome. The disease is caused by the HIV retrovirus, a specialized virus which attacks the human immune system.
Albumin: A protein in many animal and vegetable tissues, including human plasma.
Amino Acids: Any organic acid containing one or more amino groups (NH2) and a carboxyl group (CO2H); forming the essential components of proteins.
Ammonia: A colorless, volatile, pungent alkaline gas, soluble in water; formed by the body as a product of protein metabolism; converted to urea by the liver or excreted by the kidney.
Antibody: A three-lobed globulin containing two short and two long chains of protein, found in blood and other body fluids, that can be incited by the presence of antigen; it has a destructive influence on the antigen that stimulated its formation, thus producing immunity. B-cells bombard viral particles with antibodies until they find one which works, and then manufacture large quantities of the effective antibody and release it into the blood . They also retain a memory of these antibodies - if the virus ever attempts to reinfect the body, B-cells quickly manufacture the
remembered antibody and wipe it out.
Antigenic drift: Many viruses mutate frequently in order to avoid destruction by the immune systems of their hosts. The gradual evolution of viral strains that results from these mutations is known as antigenic drift.
Antisense strand: Most genetic material, both DNA and RNA, appears as two chains or strands of nucleotides wound together into a double helix - the common picture of DNA. Each nucleotide - A, T, C and G - has an attractive opposite (A attracts T, C attracts G). As a result, one strand, the "sense" strand, contains the information (for example, ATG-AAA) and the other strand, the "antisense" strand contains the opposite of this information (TAC-TTT - according to the pairing rules). Antisense RNA is the "antisense" half of a complete double RNA strand. RNA viruses consist of two types - "sense" RNA viruses, whose genetic material consists of the "sense" half of a complete strand, and "antisense" RNA viruses, which have the "antisense" half. Sense RNA viruses can have their genetic material read out directly by the ribosomes of their host cells - antisense RNA viruses must first copy themselves into a "sense" strand of RNA.
Asymptomatic: Free of symptoms.
B Cell: One of the two major types of lymphocytes (white blood cells), derived from bone marrow lymphocytes.
Bacteria: Any of various one-celled microorganisms of the plant
kingdom, existing as free- living organisms or as parasites of other organisms. Bacteria reproduce through subdivision, and are classified according to their shape and behavior.
Bacteriophage: A very delicate bacterial virus with considerable variation in structure which may attack and destroy bacteria cells under certain conditions; it contains a nucleic acid core and a protein coat.
Blood sugar: The carbohydrate, principally glucose, of the blood.
Blood transfusion: Introduction of new matching blood into the bloodstream.
Budding: Cells are constantly sampling their outside environment, taking in substances from outside of the cell, as well as releasing substances to the external environment - in this way, cells can communicate with one another to form complex organisms. This is typically accomplished through budding: the cell membrane bends inward or outward and closes in upon itself, forming a "bubble" of membrane for the transport of substances. Many viruses utilize this mechanism as a method of entry and exit from a host cell - they are carriend into the cell when it buds inward, and released when it buds outward. Many viruses retain the "bubble" of cell membrane (lipid), creating a protective lipid envelope for themselves - thus these viruses' development is completed as they are released from the cell and simultaneously given their lipid envelope.