Terminology

Agonist - A substance that mimics the cellular effects of a natural compound (such as a hormone or neurotransmitter) by binding to and activating the same cellular receptor.

Alkaloids - A large group of nitrogenous basic substances found in plants. Most of them taste bitter, and many are pharmacologically active. They are derived as a result of aromatic amino acid metabolism.

Ames Test - A test for the mutagenicity of a substance. A strain of the bacterium Salmonella typhimurium having a mutation that disables an enzyme necessary for histidine utilization is exposed to the substance in question and plated on a medium lacking histidine. A reversion mutation that activates the mutant enzyme causes the cells to grow on this medium.

Antagonist - A substance that counteracts the cellular effects of a natural compound (such as a hormone or neurotransmitter) by binding to the cellular receptor for the compound and blocking its action.

Antihistamines - Substances used to treat allergies and other inflammations by blocking histamine production.

Auxotroph - Microorganism strains that require a particular substance as a nutrient that is not required by the prototype strain. Usually the requirement results from a mutation that disables an enzyme necessary for the endogenous synthesis of the substance.

Catecholamines - A class of dihydroxylated molecules, such as dopa, dopamine, norepinephrine, and epinephrine, which are derived from tyrosine in animals. Figure 21.32

Chemotaxis - The process by which bacteria sense a concentration gradient of a particular substance in the medium and move either up or down the gradient.

Cholinergic Synapse - Synapses in neurotransmission involving acetylcholine. Figure 21.33

Dopaminergic Neurons - Neurons secreting dopamine.

Electrical Synapses - Synapses frequently found in animals that live in cold environments that need to make quick motions. These involve direct electrical-ionic conduction between nerve cells, using gap junctions.

Endorphins - Small peptides acting as neurohormones that are responsible for the insensitivity to pain that is experienced under conditions of great stress or shock.

Enkephalins - Small peptides acting as neurohormones that are responsible for the insensitivity to pain that is experienced under conditions of great stress or shock. Examples include -endorphin, met-enkephalin, and others.

Excitatory Neurotransmission - Neurotransmission in which an action potential is promoted in the postsynaptic cell. Examples include nicotinic cholingergic synapses and those involving glutamate.

Glutathione S-transferases - Enzymes involved in detoxification of many substances, such as xenobiotics or electrophiles produced through the action of cytyochrome-P-450-linked oxidases.

Histidine Operon - A set of 10 bacterial genes for histidine biosynthesis under coordinated transcriptional regulation.

Homocystinuria - A condition caused by deficiencies of one of three enzymes in cysteine metabolism. In this patients, homocystine accumulates and is excreted in the urine. Figure 21.9

Inhibitory Neurotransmission - Neurotransmission, such as that involving GABA or muscarinic acetylcholine receptors, in which impulses received at a synapse discourages transmission of an action potential in the recipient neuron.

Melanocytes - Pigment-producing cells involved in synthesis of melanins

Muscarinic Acetylcholine Receptor - A class of receptors for the neurotransmitter acetylcholine that are characterized by an ability to bind the toadstool toxin muscarine. Synapses that have these receptors may be either excitatory or inhibitory.

Neurohormones - Substances in nervous systems that modify the way in which nerve cells respond to transmitters.

Neurotransmitter - Chemical messenger(s) released by presynaptic nerve cells which bind to postsynaptic cells.

NIH Shift - A reaction named after scientists at the National Institutes of Health who described a ring hydroxylation that proceeds via formation of an epoxide intermediate.

Ovothiol - A sulfur amino acid found in fertilized eggs that plays a role similar to glutathione

Presynaptic Axon - Nerve cell carrying action potential to the terminal bulb. Figure 21.33

Prototroph - An unmutated form of an organism which is able to synthesize a particular metabolite. Mutation of this type of organism creates an auxotroph.

Synaptic Vesicles - Structures on the terminal bulb of the presynaptic axon that release acetylcholine (in cholinergic synapses) in respose to calcium. Figure 21.33

Terminal Bulb (synaptic knob) - Part of the presynaptic axon separated from the postysynaptic dendrite by a synaptic cleft about 20 nm wide. It contains the synaptic vesicles and a change in membrane potential in it causes opening of voltage-gated calcium channels to open, allowing Ca⁺⁺ ions to pass from the surrounding space into the axonal bulb. Figure 21.33

Tetrapyrrole - A generic term for compounds containing four linked pyrrole rings.

Thyroglobulin - Protein containing tyrosine residues which are iodinated to create thyroid hormone. Figure 21.19

Transamination - The enzymatic transfer of an amino group from an amino acid to a keto-acid. The keto-acid becomes an amino acid and vice versa.

Transmethylations - The type of reactions involving most of the group transfers of AdoMet.

Vacuolar ATPase - An enzyme that pumps protons into synaptic vesicles, an essential step in transporting acetylcholine.