Biology Solomon, 8Th Edition Chapter 5

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phospholipid

Back 1

Lipids in which two fatty acids and a phosphorus-containing group are attached to glycerol; major components of cell membranes.

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amphipathic

Back 2

"Of two minds". Amphipathic lipid, in which one end of each molecule is hydrophilic and the other end is hydrophobic.

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fluid mosaic model

Back 3

The currently accepted model of the plasma membrane and other cell membranes, in which protein molecules "float" in a fluid phospholipid bilayer.

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integral membrane protein

Back 4

A protein that is tightly associated with the lipid bilayer of a biological membrane; a transmembrane integral protein spans the bilayer.

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peripheral membrane protein

Back 5

A protein associated with one of the surfaces of a biological membrane.

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transmembrane protein

Back 6

An integral membrane protein that spans the lipid bilayer.

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glycoprotein

Back 7

A protein with covalently attached carbohydrates.

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signal transduction

Back 8

A process in which a cell converts and amplifies an extracellular signal into an intracellular signal that affects some function in the cell.

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selective permeable membrane

Back 9

A membrane that allows some substances to cross it more easily than others. Biological membranes are generally permeable to water but restrict the passage of many solutes.

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transport protein

Back 10

Move ions, amino acids, sugars, and other needed polar molecules through membranes. They apparently evolved very early in the origin of cells. Found in all biological membranes.
Two main types of transport proteins: carrier and channel proteins.

Front 11

phospholipid

Back 11

Lipids in which two fatty acids and a phosphorus-containing group are attached to glycerol; major components of cell membranes.

Front 12

amphipathic

Back 12

"Of two minds". Amphipathic lipid, in which one end of each molecule is hydrophilic and the other end is hydrophobic.

Front 13

fluid mosaic model

Back 13

The currently accepted model of the plasma membrane and other cell membranes, in which protein molecules "float" in a fluid phospholipid bilayer.

Front 14

integral membrane protein

Back 14

A protein that is tightly associated with the lipid bilayer of a biological membrane. Cell biologists usually can release them only by disrupting the bilayer with detergents. These proteins are amphipathic. Their hydrophilic regions extend out of the cell or into the cytoplasm, whereas their hydrophobic regions interact with the fatty acid tails of the membrane phospholipids.

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peripheral membrane protein

Back 15

A protein associated with one of the surfaces of a biological membrane. Peripheral membrane proteins are not embedded in the lipid bilayer. They are located on the inner or outer surface of the plasma membrane, usually bound to exposed regions of integral proteins by noncovalent interactions. Peripheral proteins can be easily removed from the membrane without disrupting the structure of the bilayer.

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transmembrane proteins

Back 16

Integral proteins that extend completely through the membrane. The most common kind of transmembrane protein is an a-helix with hydrophobic amino acid side chains projecting out from the helix into the hydrophobic region of the lipid bilayer. Some proteins span the membrane in the form of rolled-up B-pleated sheets. These protein formations are barrel shaped and form pores through which water and other substances can pass.

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diffusion

Back 17

The net movement of particles (atoms, molecules, or ions) from a region of higher concentration to a region of lower concentration (i.e., down a concentration gradient), resulting from random motion.

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concentration gradient

Back 18

A difference in the concentration of a substance from one point to another, as for example, across a cell membrane.

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dynamic equilibrium

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The condition of a chemical reaction when the rate of change in one direction is exactly the same as the rate of change in the opposite direction, i.e., the concentrations of the reactants and products are not changing, and the difference in free energy between reactants and products is zero.

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osmosis

Back 20

The diffusion of water.

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osmotic pressure

Back 21

The pressure that must be exerted on the hypertonic side of a selectively permeable membrane to prevent diffusion of water (by osmosis) from the side containing pure water.

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isotonic

Back 22

A term applied to solutions that have identical concentrations of solute molecules and hence the same osmotic pressure.
When a cell is placed in a fluid with exactly the same osmotic pressure (isotonic), no net movement of water molecules occurs, either into or out of the cell. The cell neither swells nor shrinks.

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hypertonic

Back 23

A term referring to a solution having an osmotic pressure (or solute concentration) greater than that of the solution with which it is compared.
Because a hypertonic solution has a lower effective water concentration, a cell placed in such a solution shrinks as it loses water by osmosis.

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hypotonic

Back 24

A term referring to a solution having an osmotic pressure (or solute concentration) less than that of the solution with which it is compared. When a cell is placed in this type of solution, it gains water and swells.

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turgor pressure

Back 25

Hydrostatic pressure that develops within a walled cell, such as a plant cell, when the osmotic pressure of the cell's contents is greater than the osmotic pressure of the surrounding fluid.

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plasmolysis

Back 26

The shrinkage of cytoplasm and the pulling away of the plasma membrane from the cell wall when a plant cell (or other walled cell) loses water, usually in a hypertonic environment.

Front 27

channel protein

Back 27

Membrane transport proteins. Channel proteins form tunnels, called pores, through the membrane that transport specific ions down their gradients. Many of these channels are gated, which means that they can be opened and closed. Channels can only facilitate transport down a gradient. They cannot actively transport ions from a region of lower concentration to a region of higher concentration.

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aquaporin

Back 28

One of a family of transport proteins located in the plasma membrane that facilitate the rapid movement of water molecules into or out of cells. They function as gated water channels; they are very selective and do not permit passage of ions and other small molecules. They help prevent dehydration by returning water from the kidney tubules into the blood.

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gated channel

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Means that channels can be opened and closed. Cells regulate the passage of materials through the channels by opening and closing the gates in response to electrical changes, chemical stimuli, or mechanical stimuli.

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carrier protein

Back 30

(Also called transporters), bind the ion or molecule and undergo changes in shape, resulting in movement of the molecule across the membrane.

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carrier-mediated transport

Back 31

Transfer of solutes by carrier proteins located within the membrane.
There are two forms of carrier-mediated transport: facilitated diffusion and carrier-mediated active transport.

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facilitated diffusion

Back 32

A form of carrier-mediated transport. The passive transport of ions or molecules by a specific carrier protein in a membrane. As in simple diffusion, net transport is down a concentration gradient, and no additional energy has to be supplied.

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active transport

Back 33

Transport of a substance across a membrane that does not rely on the potential energy of a concentration gradient for the substance being transported and therefore requires an additional energy source (often ATP); includes carrier-mediated active transport, endocytosis, and exocytosis.

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sodium-potassium pump

Back 34

Active transport system that transports sodium ions out of, and potassium ions into, cells.

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electrical gradient

Back 35

Established by the unequal distribution, it drives ions across the plasma membrane.

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cotransport

Back 36

The active transport of a substance from a region of low concentration to a region of high concentration by coupling its transport to the transport of a substance down its concentration gradient.

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exocytosis

Back 37

The active transport of materials out of the cell by fusion of cytoplasmic vesicles with the plasma membrane.

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endocytosis

Back 38

The active transport of substances into the cell by the formation of invaginated regions of the plasma membrane that pinch off and become cytoplasmic vesicles.

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phagocytosis

Back 39

Literally "cell-eating"; a type of endocytosis by which certain cells engulf food particles, micro-organisms, foreign matter, or other cells.

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pinocytosis

Back 40

Cell drinking; a type of endocytosis by which cells engulf and absorb droplets of liquids.

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clathrin

Back 41

A layer of protein coating a "pit" (depressed regions on the cytoplasmic surface of the plasma membrane)--found just below the plasma membrane.

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coated pits

Back 42

Depressed regions on the cytoplasmic surface of the plasma membrane where LDL receptors are concentrated. (When the cell needs cholesterol, the cell makes these LDL receptors).

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ligand

Back 43

A molecule that binds specifically to a receptor.

(i.e., LDL can be a ligand)

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cell signaling

Back 44

Mechanisms of communication between cells. Cells signal one another with secreted signaling molecules, or a signaling molecule on one cell combines with a receptor on another cell.

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anchoring junction

Back 45

Connect cells of an epithelial sheet. Cadherins (transmembrane proteins) are important components of anchoring junctions. These junctions do not affect the passage of materials between adjacent cells.

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cell junction

Back 46

Cells in close contact with one another typically develop specialized intercellular junctions. These structures may allow neighboring cells to form strong connections with one another, prevent the passage of materials, or establish rapid communication between adjacent cells.

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desmosome

Back 47

Points of attachment between cells. They hold cells together at one point as a rivet or a spot weld does. As a result, cells form strong sheets, and substances still pass freely through the spaces between the plasma membranes. Made up of regions of dense material associated with the cytosolic sides of the trwo plasma membranes, plus protein filaments that cross the narrow intercellular space between them.

Front 48

adhering junctions

Back 48

Cement cells together. Cadherins form a continuous adhesion belt around each cell, binding the cell to neighboring cells.

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cadherins

Back 49

The principle cell adhesion molecules in vertebrates and in many invertebrates. These molecules are responsible for calcium-dependent adhesion between cells that form multicellular sheets. They form cell junctions important in maintaining the structure of the epithelium that makes up human skin; they can also mediate the way cells adhere in the early embryo (important in development).

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tight junction

Back 50

Areas of tight connections between the membranes of adjacent cells. These connections are so tight that no space remains between the cells and substances cannot leak between them.

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gap junction

Back 51

Is like a desmosome in that it bridges the space between cells; however, the space it spans is somewhat narrower. Gap junctions also differ in that they are communicating junctions. They not only connect the plasma membranes but also contain channels connecting the cytoplasm of adjacent cells. They are composed of connexin, an integral membrane protein.

Front 52

plasmodesmata

Back 52

Channels connecting adjacent plant cells. Openings in the cell walls allow the plasma membranes and cytosol to be continuous; certain molecules and ions pass from cell to cell.