Acetylcholine (Ach) Neurotransmitter that functions at vertebrate neuromuscular junctions and at many neuron–neuron synapses in the brain and peripheral nervous system.
Acetyl CoA An acetyl group linked to coenzyme A; formed during oxidation of pyruvate, fatty acids, and amino acids.
Acidosis A metabolic condition resulting from the accumulation of acid or the depletion of bicarbonate in the blood and tissues.
Acquired immunity The ability of an individual to produce specific antibodies in response to antigens to which the body has previously been exposed based on the development of a memory response.
Active transport The transport of solute molecules across a membrane against a concentration and/or electrical gradient; it requires a carrier protein and the input of energy.
Acyclovir A synthetic purine nucleoside derivative with antiviral activity against herpes simplex virus.
Adenylate cyclase The enzyme that catalyzes the formation of cyclic-3′,5′-adenosine monophosphate (cAMP) from ATP.
Adhesions Thin protein structures that mediate the adhesion of E. coli to epithelial surfaces and contribute to the virulence of the bacteria.
Adjuvant A drug ingredient that aids or modifies the action of the main ingredient.
Aerobic bacterium A bacterium that requires oxygen for growth and survival.
Agglutination reaction The formation of an insoluble immune complex by the cross-linking of cells or particles.
Albuminuria Abnormally high level of albumin, a plasma protein, in the urine.
Allele One of two or more alternative forms of a gene located at the corresponding site (locus) on homologous chromosomes.
α-helix A helical folding pattern found in protein backbones, α-helices are characterized by having 3.6 amino acid residues per turn.
Anabolism The synthesis of complex molecules from simpler molecules with the input of energy.
Anaerobic bacterium A bacterium that does not require oxygen for maintenance or growth.
Anaphylaxis An immediate hypersensitivity reaction following exposure of a sensitized individual to the appropriate antigen. Mediated by reagin antibodies, chiefly IgE.
Anoxic Without oxygen; anaerobic.
Antibody Large Y-shaped proteins produced by higher organisms (e.g., humans, monkeys, rodents) in response to