Rapid, transient, self-propagating electrical excitation in the plasma membrane of a cell such as a neuron or muscle cell. A major constituent of the cytoskeleton of all eucaryotic cells and part of the contractile apparatus of skeletal muscle. Helical protein filament formed by the polymerization of globular actin molecules.

Examples include myosin, α-actinin, and profilin. Protein that associates with either actin monomers or actin filaments in cells and modifies their properties. The monomeric form is sometimes called globular or G-actin the polymeric form is filamentous or F-actin. actinĪbundant protein that forms actin filaments in all eucaryotic cells. Reaction that occurs when a sperm starts to enter an egg, in which the contents of the acrosomal vesicle are released, helping the sperm to penetrate the zona pellucida. Region at the head end of a sperm cell that contains a sac of hydrolytic enzymes used to digest the protective coating of the egg. Unresponsiveness of the immune system to a given foreign antigen that can develop in some circumstances. acid hydrolaseĪny of a group of diverse hydrolytic enzymes (including proteases, nucleases, glycosidases, etc.) that have their optimal activity at acid pH (around 5.0) and are found in lysosomes. Substance that releases protons when dissolved in water, forming a hydronium ion (H 3O +). It is the neurotransmitter at vertebrate neuromuscular junctions. Found both in the brain and in the peripheral nervous system.

Neurotransmitter that functions at a class of chemical synapses known as cholinergic synapses. Sometimes called the nicotinic acetylcholine receptor to distinguish it from a muscarinic acetylcholine receptor, which is a G-protein-linked cell-surface receptor. Best understood example of a transmitter-gated channel. Ion channel that opens in response to binding of acetylcholine, thereby converting a chemical signal into an electrical one. ( See Figure 2–62.) acetylcholine receptor It consists of an acetyl group linked to coenzyme A (CoA) by an easily hydrolyzable thioester bond. Small water-soluble molecule that carries acetyl groups in cells. Acetyl groups are important in metabolism and are added covalently to some proteins as a posttranslational modification. acetylĬhemical group derived from acetic acid. Large superfamily of membrane transport proteins that use the energy of hydrolysis of ATP to transfer peptides and a variety of small molecules across membranes.

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