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Flashcards in Chapter 6 Deck (36):
1

Amphipatic

Containing hydrophilic and hydrophobic regions.

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Aquaporin

A type of channel protein through which water can move by osmosis across a plasma membrane.

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Carrier protein

A membrane protein that facilitates diffusion of a small molecule (e.g., glucose) across a membrane by a process involving a reversible change in the shape of the protein. Also called carrier or transporter. Compare with channel protein.

4

Channel protein

A protein that forms a pore in a cell membrane. The structure of most channels allows them to admit just one or a few types of ions or molecules. Compare with carrier protein.

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Concentration gradient

Difference across space (e.g., across a membrane) in the concentration of a dissolved substance.

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Detergent

A type of small amphipathic molecule used to solubilize hydrophobic molecules in aqueous solution.

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Diffusion

Spontaneous movement of a substance from one region to another, often with a net movement from a region of high concentration to one of low concentration (i.e., down a concentration gradient).

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Ester linkage

The covalent bond formed by a condensation reaction between a carboxyl group and a hydroxyl group. Ester linkages join fatty acids to glycerol to form a fat or phospholipid.

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Facilitated diffusion

Passive movement of a substance across a membrane with the assistance of transmembrane carrier proteins or channel proteins.

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Fat

A lipid consisting of three fatty acid molecules joined by ester linkages to a glycerol molecule. Also called triacylglycerol or triglyceride.

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Fatty acid

A lipid consisting of a hydrocarbon chain bonded at one end to a carboxyl group. Used by many organisms to store chemical energy; a major component of animal and plant fats and phospholipids.

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Fluid-mosaic model

The widely accepted hypothesis that the plasma membrane and organelle membranes consist of proteins embedded in a fluid phospholipid bilayer.

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Gated channel

A channel protein that opens and closes in response to a specific stimulus, such as the binding of a particular molecule or a change in voltage across the membrane.

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Glycerol

A three-carbon molecule that forms the "backbone" of phospholipids and most fats.

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Hydrocarbon

An organic molecule that contains only hydrogen and carbon atoms.

16

Hypertonic

Comparative term designating a solution that, if inside a cell or vesicle, results in the uptake of water and swelling or even bursting of the membrane-bound structure. This solution has a greater solute concentration than the solution on the other side of the membrane. Used when the solute is unable to pass through the membrane. Compare with hypotonic and isotonic.

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Hypotonic

Comparative term designating a solution that, if inside a cell or vesicle, results in the loss of water and shrinkage of the membrane-bound structure. This solution has a lower solute concentration than the solution on the other side of the membrane. Used when the solute is unable to pass through the membrane. Compare with hypertonic and isotonic.

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Integral membrane protein

Any membrane protein that spans the entire lipid bilayer. Also called transmembrane protein. Compare with peripheral membrane protein.

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Isotonic

Comparative term designating a solution that, if inside a cell or vesicle, results in no net uptake or loss of water and thus no effect on the volume of the membrane-bound structure. This solution has the same solute concentration as the solution on the other side of the membrane. Compare with hypertonic and hypotonic.

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Lipid

Any organic substance that does not dissolve in water, but dissolves well in nonpolar organic solvents. Lipids include fatty acids, fats, oils, waxes, steroids, and phospholipids.

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Lipid bilayer

The basic structural element of all cellular membranes; consists of a two-layer sheet of phospholipid molecules with their hydrophobic tails oriented toward the inside and their hydrophilic heads toward the outside. Also called phospholipid bilayer.

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Oil

An unsaturated fat that is liquid at room temperature.

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Osmosis

Diffusion of water across a selectively permeable membrane from a region of low solute concentration (high water concentration) to a region of high solute concentration (low water concentration).

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Passive transport

Diffusion of a substance across a membrane. When this event occurs with the assistance of membrane proteins, it is called facilitated diffusion.

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Peripheral membrane protein

Any membrane protein that does not span the entire lipid bilayer and associates with only one side of the bilayer. Compare with integral membrane protein.

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Permeability

The tendency of a structure, such as a membrane, to allow a given substance to diffuse across it.

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Phospholipid

A class of lipid having a hydrophilic head (including a phosphate group) and a hydrophobic tail (consisting of two hydrocarbon chains). Major components of the plasma membrane and organelle membranes.

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Plasma mmbrane

A membrane that surrounds a cell, separating it from the external environment and selectively regulating passage of molecules and ions into and out of the cell. Also called cell membrane.

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Protocell

A hypothetical pre-cell structure consisting of a membrane compartment that encloses replicating macromolecules, such as ribozymes.

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Saturated

Referring to lipids in which all the carbon-carbon bonds are single bonds. Such compounds have relatively high melting points. Compare with unsaturated.

31

Scanning electron microscope (SEM)

A microscope that produces images of the surfaces of objects by reflecting electrons from a specimen coated with a layer of metal atoms. Compare with transmission electron microscope.

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Secondary active transport

Transport of an ion or molecule in a defined direction that is often against its electrochemical gradient, in company with an ion or molecule being transported along its electrochemical gradient. Also called cotransport.

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Selective permeability

The property of a membrane that allows some substances to diffuse across it much more readily than other substances.

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Steroid

A class of lipid with a characteristic four-ring hydrocarbon structure.

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Unsaturated

Referring to lipids in which at least one carbon-carbon bond is a double bond. Double bonds produce kinks in hydrocarbon chains and decrease the compound's melting point. Compare with saturated.

36

Wax

A class of lipid with extremely long, saturated hydrocarbon tails. Harder and less greasy than fats.