MCAT Biology Glossary: A Flashcards
ABO Blood System
A classification system for the antigens of human blood; used in blood transfusion therapy; four groups are A, B, AB, and O.
Absorption
The movement of a substance, such as a liquid or solute, across a cell membrane by means of diffusion or osmosis.
Acentric chromosome
A chromosome lacking a centromere.
Acetaldehyde
A colorless, flammable liquid, C2H4O, used to manufacture acetic acid, perfumes, and drugs by means of organic synthesis.
Acetic acid
A clear, colorless organic acid, CH3COOH, with a distinctive pungent odor, used as a solvent and in the manufacture of rubber, plastics, acetate fibers, pharmaceuticals, and photographic chemicals. It is the chief acid of vinegar.
Acetylcholine (ACh)
A direct-acting cholinergic neurotransmitter agent widely distributed in body tissues, with a primary function of mediating the synaptic activity of the nervous system and skeletal muscles.
ACh is rapidly destroyed by acetylcholinesterase, and can be blocked by atropine at the junctions of nerve fibers with glands and smooth muscle tissue.
It is a vagus nerve and autonomic nervous system stimulant, and functions as a vasodilator and cardiac depressant.
Acetylcholinesterase (AChE)
An enzyme present at the endings of voluntary nerves, parasympathetic involuntary nerves, and autonomic nerve ganglia.
It inactivates and prevents the accumulation of the neurotransmitter acetylcholine (ACh) released during nerve impulse transmission by hydrolyzing the substance to choline and acetate.
This action reduces or prevents excessive firing of neurons at neuromuscular junctions.
Acetyl-CoA
A coenzyme derivative in the metabolism of glucose and fatty acids that contributes substrates to the Krebs cycle.
Acetyl-CoA provides the acetyl unit for multiple biochemical reactions, and plays a central role in intermediary metabolism-synthesis, catabolism, or use of nutrients for energy production and growth.
