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| acts as a barrier that controls the transit of molecules into and out of the cell; bilayer makes it selectively permeable |
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the most plentiful positeively charged ion outside the cell
Balanced by extracellular Cl- |
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| the most plentiful positively charged ion inside the cell |
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| small nonplolar molecules |
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| readily dissolve in lipid bilayers and diffuse easily; necessary for cellular respiration |
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| uncharged polar molecules |
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Definition
| diffuse rapidly across a bilayer if they are small enough |
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| ions and charged molecules |
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Definition
| strong electrical attraction to water molecules inhibit them from entering the hydrocarbon phase of the bilayer |
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| discriminates mainly on the basis of size and electric charge. if the channel is open, molecules small enough and carrying the appropriate charge can slip through (trapdoor) |
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| allows passage only to solute molecules that fit into a binding site on the protein (extrememly selective); then it transfers these molecultes across the membrane one at a time by changing its own conformation (turnstile rather than open door). used for almost all small organic molecules across cell membranes. also present in the inner membrane of mitochondria |
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| do not require expenditure of energy by transport protein. moves from an area of high concentration to an area of low concentration. |
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| carried out only by special types of carrier proteins that can harness some energy sourse to the transport process. area of low concentration to an area of high concentration |
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| the net force driving a charged solute across the mebrane that is a composite of two forces, one due to the concentration gradient and the other due to the voltage across the membrane. determines the direction of passive transport. |
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| pump/enzyme that hydrolyzes ATP to ADP while coupling the outward transport of NA+ to an inward transport of K+ |
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| membrane transport process in which the transfer of one molecule depends on the simultaneous or sequential transfer of a second molecule; if one of the co-transported solutes is absent, transport of its companion cannot occur |
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| coupled transport in the same direction across the membrane |
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| moves solutes in opposite directions across the membrane |
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| one type of solute transported across the membrane |
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| movement of water from a region of low solute concentration to a region of high solute concentration |
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| the driving force for the water movement is equivalent to a difference in water pressure |
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| makes it possible to detect and measure the electrc current flowing through a single channel molecule. provides a direct and surprising picture of how indiviudual ion channels behave. |
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| the probability of being open is controlled by the membrane potential; electrical signals/ nerve cells |
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| it is controlled by the binding of some molecule (the ligand) to the channel protein |
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| an electrical potential difference or detectable accumulation of electric charge brought on by the ion flow across a cell membrane |
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| quantitative expression that relates the equilibrium ratio of concentrations of an ion on either side of a permeable membrane to the voltage difference across the membrane. |
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| nerve cells whose job is to recieve, conduct, and transmit signals inward from the sense organs to the central nervous system |
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| a long, thin extention radiating outward from the cell that conduct signals away from the cell body toward distant target cells |
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| the ending of an axon from which signals are sent to adjoining cells, usually at a synapse |
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| a nerve impulse; a local electrical stimulus of sufficient strength that triggers an explosion of electrical activity in the plasma membrane that is propagated rapidly along the membrane of the axon and sustained by automatic renewal all along the way |
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