base

1. the foundation or support on which something rests; the point of attachment of a part; the principal ingredient of a material. n 2. a compound that yields hydroxyl ions in water solution and causes neutralization of acid to form a salt and water.

1. A proton (hydrogen ion) acceptor.

2. In anthropometry, a firm horizontal surface on which the subject stands during body measurements. See also base of support.

1. the lowest part or foundation of anything. See also basis.
2. the main ingredient of a compound.
3. a molecule or ion with a tendency to take up a proton according to Bronsted and Lowry theory; a substance that combines with acids to form salts. In the chemical processes of the body, bases are essential to the maintenance of a normal acid–base balance. Excessive concentration of bases in the body fluids leads to alkalosis. See also basal.
4. the primary entity against which all other entities are compared.
5. the non-sugar components of nucleotides in DNA and RNA.

• acid–b. pairs — the two molecules forming the matching acid and conjugate base.
• b. composition — refers to the relative components of a nucleic acid.
• conjugate b. — the anion or uncharged molecule of an acid once it has given up its proton, e.g. Cl⁻ is the conjugate base of the acid, HCl.
• b. deficit — see base excess (below).
• b. excess — the amount of acid or base required to titrate a sample of whole arterial blood to the normal pH of 7.4. The base excess is determined mathematically by calculations that include measurement of the blood Pco₂ and pH and take into account the hemoglobin level. It is negative (base deficit) in acidosis and positive in alkalosis.
• heart b. — the wide dorsal part of the heart carrying the atria and the large blood vessels and the attachment to the pericardial sac.
• horn b. — the widest part of the horn, at its attachment to the skin. In the adult horned animal the horn is hollow at this point, encloses the horn process of the frontal bone and merges with the skin. This is covered with a thin layer of horn similar to the periople of the hoof, called the epiceras.
• narrow b. — a mandible which is narrow relative to the maxilla; often causes the lower canine teeth to strike the hard palate. See also anisognathism.
• nitrogenous b. — an aromatic, nitrogen-containing molecule that serves as a proton acceptor, e.g. purine or pyrimidine.
• omasal b. — faces cranially and to the left where it is attached to the reticulum and the abomasum at the reticulo-omasal and omasoabomasal orifices.
• b. pair — two hydrogen bonded nucleotides in a DNA or RNA molecule.
• purine b's — a group of compounds of which purine is the base, including uric acid, adenine, guanine, xanthine and theobromine.
• pyrimidine b's — a group of chemical compounds of which pyrimidine is the base, including uracil, thymine and cytosine, which are common constituents of nucleic acids.
• stapedal b. — the footplate of the stapes in the middle ear from which the two legs originate. The stapes lies horizontally with the base facing medially and attached to the vestibular window by the annular ligament.