A chemical neurotransmitter that is expelled into the synaptic cleft,or space between two nerve cells. This neurotransmitter permits the transmission of an electrical nerve impulse or action potential from one nerve cell to another by diffusing across the...[继续阅读]

    An enzyme present in the synaptic cleft,or space between two nerve cells,that hydrolyzes or destroys the unbound neurotransmitter acetylcholine once it has diffused through the cleft. This is required to restore the synaptic cleft to a state that is ready...[继续阅读]

    Certain sequences of amino acids on a protein that bind to a transcriptional regulatory protein and,in so doing,serve to activate transcription.蛋白质上特定的氨基酸序列,可以与转录调控蛋白结合,从而激活转录。...[继续阅读]

    The hypothesis that elongation of plant cells caused by the plant hormones known as auxins involves a mechanism for creating an acid environment (lowered pH) in the specific region of the cell where growth is to occur. The acidification of a plant cell in...[继续阅读]

    The two amino acids that are negatively charged at pH 7.0 are aspartic and glutamic acids. Also referred to as aspartate or glutamate. Both of these amino acids contain in their R or variable groups a second carboxyl group that is ionized under physiologi...[继续阅读]

    A classification of microorganisms that describes the ability or the necessity of certain species to exist in an acidic environment. These acid-loving organisms can exist at a pH range of 0-5.4,well below the optimum of neutrality for most bacteria.Facult...[继续阅读]

    An infectious disease in humans caused by the human immunodeficiency virus (HIV). The virus attacks the host’s immune system leaving him/her susceptible to many other diseases,including certain rare forms of cancer and opportunistic microbial infections t...[继续阅读]

    One of a group of chemical mutagens known as acridines,including proflavin and acriflavine. The size of the acridines is the same as that of a purinepyrimidine base pair. For this reason,they can insert or intercalate into the helix between two adjacent b...[继续阅读]

    A vesicle- or membrane-bound compartment covering the sperm head that contains lytic enzymes. The major enzyme found in the mammalian sperm acrosome is hyaluronidase,which promotes the digestion of the tough outer coat of the egg and allows penetration of...[继续阅读]

    A substance that can polymerize and form a slab gel when poured into a mold in its molten state. It is used as semisolid support medium and is immersed in a conductive buffer through which a current is passed. When solutions containing heterogeneous mixtu...[继续阅读]