A muscle that moves a limb away from the center of the body.

Three dimensional orientation in space of the four substituents on a chiral center (ie. the R or S configuration of a chiral carbon).

Stable compounds of the general formula R₂(OR\')₂, resulting from the nucleophilic addition of 2 moles of an alcohol to an aldehyde. Often used as a protecting group for aldehydes, because they are stable to basic and nucleophilic reagents but easily removed by acid hydrolosis.

A neutrotransmitter found throughout the nervous system (eg. somatic motor neurons, preganglionic parasympathetic and sympathetic nerves, and postganglionic parasympathetic nerves). It is metabolized by acetylcholinesterase.

A molecule that does not possess optical activity.

The large vesicle at the head of a sperm cell containing enzymes that degrade the ovum cell membrane and allow fertilization.

A protein found in the cytoskeleton and muscle cells; it is the principal constituent of the thin filament.

An abrupt change in the membrane potential of a nerve or muscle cell caused by changes in ionic permeability. Results in conduction of an impulse in nerves or contraction in muscles.

Activating groups make an aromatic ring more susceptible to electrophilic substitution. Activating groups, except for alkyl groups, have at least one pair of nonbonding electrons on the atom directly attached to the ring; these electrons stabilize the carbocation intermediate. Activating groups direct substituents to the ortho and para positions. Typical examples are -NH₂, -OH, -CH₃, and -OCH₃.

An immune response (antibody production or cellular immunity) acquired in response to exposure to an antigen.

Substrate-binding region of an enzyme.

The use of energy to move a substance across a membrane against a concentration gradient.