Terminology

Actin - A peripheral membrane protein of erythrocytes, it helps to link spectrin to the membrane at its ends and is also complexed with an erythrocyte-specific tropomyosin (Figure 10.18).
Action Potential - A wave of transient depolarization that travels along the membrane of a nerve cell (or any other kind of excitable cell, such as a muscle cell) as a result of fluxes of ions across the membrane. A nerve impulse (Figure 10.31).
Active Transport - A mechanism for transporting materials across a membrane irrespective of the concentration gradient. Generally materials are transported against a concentration gradient at the expense of free energy.
Adipocytes - Animal cells specialized for fat storage.
Amphipathic - For a molecule, the property of having both hydrophobic and hydrophilic portions. Usually one end or side of the molecule is hydrophilic and the other end or side is hydrophobic.
Anion Channel Protein (Band 3 protein) - An integral protein of the erythrocyte membrane. It is attached to spectrin by the protein called adducin. The function of this protein is to allow the passage of bicarbonate and chloride ions through the membrane and thereby facilitate carbon dioxide transport by the hemoglobin. It may associate with glyceraldehyde-phosphate dehydrogenase. The N-terminal domain of this protein is associated with the peripheral protein, ankyrin (Figure 10.18).
Ankyrin - A peripheral protein that is part of the erythrocyte membrane skeleton. It serves to link the skeleton to the band 3 (anion channel) integral protein (Figure 10.18).
Antiport - A transport system in which two substances are transported in opposite directions.
Arachidonic Acid/Arachidonate - An unsaturated fatty acid containing 20 carbons and a cis double bonds 5, 8, 11, and 14 carbons away from the carboxyl group. Arachidonate is the ionized form of arachidonic acid. The systematic name is all-cis-5, 8, 11, 14-Eicosatetraenoic acid. Arachidonic acid is a precursor of the prostaglandins (Table 10.1).
Axon - A threadlike process extending from a nerve cell by which impulses are transmitted to other nerve cells or to effector cells such as muscle or gland cells. Most nerve cells have one. Shorter processes that function in receiving impulses from other neurons are called dendrites (Figure 10.29).
Band 4.1 Protein - A peripheral membrane protein of erythrocytes found at junctions of spectrin (Figure 10.18).
Behenic Acid/Behenate - A saturated fatty acid with 22 carbons. Behenate is the ionized form of behenic acid. The systematic name is n-Docosanoic acid (Table 10.1).
Capric Acid/Caprate - A saturated fatty acid with 10 carbons. Caprate is the ionized form of capric acid. The systematic name is n-Decanoic acid (Table 10.1).
Carrier-Facilitated Transport - A mechanism of facilitated transport in which a molecule binds another molecule to be transported and rapidly moves it across a membrane, depositing it on the other side. An example is valinomycin, which selectively transports potassium ions across the membrane (Figure 10.20).
Ceramide - A sphingolipid made by combining sphingosine with an acyl group, forming an amide bond (Figure 10.8).
Cerebroside - A sphingolipid which is important in the membranes of brain and nerve cells. These are ceramides onto which a sugar moiety has been added.
Cerotic Acid/Cerotate - A saturated fatty acid with 26 carbons. Cerotate is the ionized form of cerotic acid. The systematic name is n-Hexacosanoic acid (Table 10.1).
Cholesterol - An important lipid constituent of membranes that also is implicated in atherosclerosis. It serves as a precursor to the steroid hormones (Figure 10.9).
Cotransport System - Active transport system that indirectly uses energy from ATP hydrolysis to drive transport of molecules across a cell membrane against a concentration gradient.
Dendrites - Short threadlike process extending from a nerve cell that receive impulses from other neurons (Figure 10.29).

Electrogenic - A transport system which, as a result of moving materials across a membrane, causes a net movement of ionic charge to occur.

Electroneutral - A transport system which, as a result of moving materials across a membrane, causes no net movement of ionic charge to occur.
Erythrocyte Ghost - The remnants of an erythrocyte created by gentle lysing of such a cell to release its diffusible contents.
Facilitated Transport (Facilitated Diffusion) - A transport process employing diffusion as the driving force, but employing special membrane carriers or pores to facilitate the movement of specific molecules across the membrane at a very high rate (Figure 10.20).
Fats - Triacylglycerols which are solid at room temperature.
Fatty Acids - These are the simplest lipids. They contain a hydrophobic tail, typically of 10-20 carbons attached to a carboxyl group (Figure 10.1).
Fluid Mosaic Model - A model, originally proposed by S. J. Singer and G.L. Nicholson, describing cellular membrane structure, according to which the proteins are embedded in a phospholipid bilayer and are free to move in the plane of the membrane (Figure 10.10).
Ganglioside - A sphingolipid which is important in the membranes of brain and nerve cells. These are ceramides onto which a complex carbohydrate is attached (Figure 10.8).
Gated Channels - A system in nerve cells in which systems for passage of sodium and potassium ions are rigidly controlled.
Glucose Transport Protein - A 492 amino acid residue membrane protein in erythrocytes responsible for transporting glucose by facilitated diffusion.
Glyceraldehyde Phosphate Dehydrogenase - An enzyme of the glycolytic pathway that also is a peripheral protein of the erythrocyte membrane.
Glycerol - A molecule forming the backbone of fats, oils, and glycerophospholipids.
Glycerophospholipids (phosphoglycerides) - Glycerol-based lipids, typically containing a phosphate group at position #3 and either one or two fatty acids on the other glycerol carbons (Figure 10.7).
Glycolipids - Lipids that contains saccharide groups.
Glycophorins - Major integral erythrocyte membrane proteins. Each has an external carbohydrate-carrying domain that may be involved in cellular recognition.
Glycosphingolipids - Sphingolipids containing a carbohydrate moiety. Both cerebrosides and gangliosides are glycosphingolipids (Figure 10.8).
Goldman Equation - An equation that takes into account the peremability of the membrane to different ions in determining the membrane potential.
Gramicidin A - A facilitated transport system produced by the bacterium Bacillus brevis that is an ionophore that permits passage of potassium and (to a lesser extent) sodium ions through it, destroying the cellular gradient for these ions (Figure 10.22).
Hydrogenation - A process in which double bonds in unsaturated fatty acids are saturated using hydrogen.
Hydrophilic - Refers to the ability of an atom or a molecule to engage in attractive interactions with water molecules. Substances that are ionic or can engage in hydrogen bonding have this property.
Hydrophobic - The molecular property of being unable to engage in attractive interactions with water molecules. Substances with this property are nonionic and nonpolar; they are nonwettable and do not readily dissolve in water.
Hydrophobicity Index - A measure of the hydrophobicity of an amino acid sequence in a polypeptide as a function of distance along it (Figure 10.16).
Integral Membrane Proteins - Proteins found in cell membranes that are embedded in both halves of the lipid bilayer and project through the membrane (Figure 10.15).
Ion Pumps - A system of active transport that moves ions against a concentration gradient across a membrane.
Ionophores - Transport systems (pores or carriers) which facilitate the transport of ions across a membrane.
Lateral Diffusion - A term describing a type of motion in lipid bilayers in which movement occurs parallel to the membrane surface, as opposed to flipping on either side of the surface.
Lauric Acid/Laurate - A saturated fatty acid with 12 carbons. Laurate is the ionized form of lauric acid. The systematic name is n-Dodecanoic acid (Table 10.1).
Lignoceric Acid/Lignocerate - A saturated fatty acid with 24 carbons. Lignocerate is the ionized form of lignoceric acid. The systematic name is n-Tetracosanoic acid (Table 10.1).
Linoleic Acid/Linoleate - An unsaturated fatty acid containing 18 carbons and cis double bonds at positions 9 and 12 carbons away from the carboxyl group. Linoleate is the ionized form of linoleic acid. The systematic name is cis,cis-9,12-Octadecadienoic acid (Table 10.1).
Linolenic Acid/Linolenate - An unsaturated fatty acid containing 18 carbons and cis double bonds 9, 12, and 15 carbons away from the carboxyl group. Linolenate is the ionized form of linoleic acid. The systematic name is all-cis-9,12,15-Octadecatrienoic acid (Table 10.1).
Lipid Bilayer - A membrane structure that can be formed by amphipathic molecules in an aqueous environment; it consists of two back-to-back layers of molecules, in each of which the polar head groups face the water and the nonpolar tails face the center of the membrane. The fabric of cellular membranes is a lipid bilayer (Figure 10.5).
Lipids - A chemically diverse group of biological compounds that are classified together on the basis of their generally apolar structure and resulting poor solubility in water.
Lipoproteins - A class of molecules in which lipids are bound to proteins.
Micelles - Tiny droplets that form when an amphipathic substance that has a polar head group and a nonpolar tail region (such as a fatty acid) is added to an aqueous medium and shaken. Each droplet consists of a spherical cluster of amphipathic molecules arranged with their polar head groups facing out toward the water and their nonpolar tails facing in toward the center (Figure 10.5).
Monolayers - An arrangement of molecules, typically on the surface of a liquid, in which only a single layer of such molecules are present.
Myelin Sheath - An insulating membrane provided around axons by Schwann cells (Figure 10.29).
Myristic Acid/Myristate - A saturated fatty acid with 14 carbons. Myristate is the ionized form of myristic acid. The systematic name is n-Tetradecanoic acid (Table 10.1).
Nernst Equation - An equation that relates the electrical potential across a membrane to the concentrations of ions on either side of the membrane. Equation 10.8
Neurotoxins - A toxin that acts by disrupting nerve cell function. Fast-acting ones often act by blocking the action of an ion gate necessary for the development of an action potential.
Neurotransmitter - A substance which enables nerve impulses to be transmitted from one cell to another.
Nodes of Ranvier - Gaps between Schwann cells on an axon. These regions are non-myelinated (Figure 10.29).
Oleic Acid/Oleate - An unsaturated fatty acid containing 18 carbons and a single cis double bond. Oleate is the ionized form of oleic acid. The systematic name is cis-9-Octadecenoic acid (Figure 10.1, Table 10.1).
Ouabain - A glycoside which can inhibit the sodium-potassium pump by binding to its outer surface (Figure 10.25).
Palmitic Acid/Palmitate - A saturated fatty acid with 16 carbons. Palmitate is the ionized form of palmitic acid. The systematic name is n-Hexadecanoic acid (Table 10.1).
Palmitoleic Acid/Palmitoleate - An unsaturated fatty acid containing 16 carbons and a single cis double bond nine carbons away from the carboxyl group. Palmitoleate is the ionized form of palmitoleic acid. The systematic name is cis-9-Hexadecenoic acid (Table 10.1).
Passive Transport (Passive Diffusion) - A transport process accomplished by the random wandering of molecules through membranes. The process is the same as the Brownian motion of molecules in any fluid. The driving force is the concentration gradient between the two regions and the process ultimately results in the free concentration of the diffusing substance being the same on both sides of the membrane.
Peripheral Membrane Proteins - Proteins found in cell membranes that are embedded in only one half of the lipid bilayer and do not project through the membrane (Figure 10.10).
Phosphatidic Acid - The simplest class of glyerophospholipids, with fatty acids at carbons 1 and 2 of glycerol and a phosphate on carbon 3 (Figure 10.7).
Phosphatidylcholine - A glycerophospholipid and prominent membrane lipid in which phosphatidic acid is esterified through the phosphate group to choline (Figure 10.7).
Phosphatidylethanolamine - A glycerophospholipid and prominent membrane lipid in which phosphatidic acid is esterified through the phosphate group to ethanolamine (Figure 10.7).
Phosphatidylinositol - A glycerophospholipid in which phosphatidic acid is esterified through the phosphate group to inositol.
Phosphatidylserine - A glycerophospholipid and prominent membrane lipid in which phosphatidic acid is esterified through the phosphate group to serine (Figure 10.7).
Phospholipids - Lipids, such as the glycerophospholipids, which contain a phosphate group.
Pore-Facilitated Diffusion - An example of this type of facilitated transport is exhibited by Band 3 protein of erythrocyte membranes, which preferentially permits chloride and bicarbonate ions to pass through the membrane (Figure 10.20).
Resting Potential - The voltage difference that exists across the membrane of an excitable cell, such as a nerve cell, except in places where an action potential is in progress. It is a consequence of the ion gradients that are maintained across the membrane.
Saponification - The process of making a soap in which a fat is hydrolyzed with an alkali, such as NaOH or KOH.
Saturated Fatty Acid - A fatty acid containing no double bonds.
Saxitoxin - A neurotoxin contained in the marine dinoflagellates responsible for 'red tide.' It binds to the sodium channel of nerve cells.
Schwann Cells - Specialized cells which envelop an axon in layers of an insulating myelin membrane (Figure 10.29).
Selective Membrane Permeability - The property of a membrane in which specific 'gates' preferentially promote the passage of materials, often only in one direction.
Soap - A class of compounds produced by hydrolzying a fat with an alkali, such as NaOH or KOH.
Sodium Dodecyl Sulfate (SDS) - A synthetic detergent that does not precipitate in hard water.
Sodium-Potassium Pump - An ion pump employing the energy of ATP to move three ions of sodium outside of the cell as two ions of potassium are moved in (Figure 10.25).
Spectrin - A peripheral protein of the erythrocyte membrane with and subunits. Is actually a chain-like fiber linking the components of the membrane skeleton (Figure 10.18).
Sphingolipids - A major class of membrane constituents built on the long-chain amino alcohol sphingosine, rather than on glycerol.
Sphingomyelin - A sphingolipid combining a ceramide with a phosphocholine (see here).
Sphingosine (D-4-sphinganine) - The backbone of the sphingolipids (see here).
Stearic Acid/Stearate - A saturated fatty acid with 18 carbons. Stearate is the ionized form of stearic acid. The systematic name is n-Octadecanoic acid. Table 10.1.
Steroids - A group of substances formed from cholesterol. They include a number of important hormones, including the sex hormones of higher animals (Figure 10.9).
Symport - A transport system in which two substances are transported in the same direction.
Tetrodotoxin - A neurotoxin found in some organs of the puffer fish that acts by preferentially binding to the sodium channel of nerve cells, blocking all ion movement.
Transition Temperature - The temperature at which a lipid bilayer converts between an ordered gel-like structure and a less ordered liquid-like structure.
Translocase - An enzyme catalyzing transverse movement (flip-flopping) of phospholipids across a lipid bilayer.
Transport by Modification - An active transport system which moves materials across the membrane against concentration gradients by modifying the molecule in transit.
Transverse Diffusion - A term describing a type of motion in lipid bilayers (relatively rare) in which movement occurs by flipping on either side of the surface, as opposed to moving parallel to the surface.
Triacylglycerol - A storage form of fatty acids in organisms (also known as fat or oil). These substances are triesters of fatty acids and glycerol (Figure 10.2).
Tristearin - A triacylglycerol in which all of the acyl groups come from stearic acid.
Triton X-100 - A synthetic non-ionic detergent.
Unsaturated Fatty Acid - A fatty acid containing at least one double bond. Double bonds in fatty acids are almost always in the cis configuration.
Valinomycin - A carrier facilitated transport system produced by Streptomyces, which selectively transports potassium ions across a membrane, destroying the concentration gradient for this ion (Figure 10.23).
Veratridine - A neurotoxin found in the seeds of Schoenocaulon officinale which binds to sodium channels of nerve cells and blocks them in the open configuration.
Wax - A class of compounds formed by esterification of fatty acids and long-chain alcohols. Used as a water repellant by organisms (Figure 10.4).