Chapter 7 - Membrane Structure and Function

Question 1

fluid mosaic model

Answer 1

The currently accepted model of cell membrane structure, which envisions the membrane as a mosaic of protein molecules drifting laterally in a fluid bilayer of phospholipids.

Question 2

integral proteins

Answer 2

A transmembrane protein with hydrophobic regions that extended into an often completely span the hydrophobic interior of the membrane and with hydrophilic regions in contact with the aqueous solution on one or both sides of the membrane (or lining the channel in the case of a channel protein).

Question 3

peripheral proteins

Answer 3

A protein loosely bound to the surface of a membrane or to part of an integral protein and not embedded in the lipid bilayer.

Question 4

glycolipid

Answer 4

A lipid with one or more covalently attached carbohydrates.

Question 5

glycoprotein

Answer 5

A protein with one or more covalently attached carbohydrates.

Question 6

transport protein

Answer 6

A transmembrane protein that helps a certain substance or class of closely related substances to cross the membrane.

Question 7

aquaporin

Answer 7

A channel protein in the plasma membrane of a plant, animal, or microorganism cell that specifically facilitates osmosis, the diffusion of free water across the membrane.

Question 8

amphipathic

Answer 8

Having both a hydrophilic region and a hydrophobic region.

Question 9

selective permeability

Answer 9

A property of biological membranes that allows them to regulate the passage of substances across them.

Question 10

diffusion

Answer 10

The spontaneous movement of a substance down its concentration or electrochemical gradient, from a region where it is more concentrated to a region where it is less concentrated.

Question 12

concentration gradient

Answer 12

A region along which the density of a chemical substance increases or decreases.

Question 13

passive transport

Answer 13

The diffusion of a substance across a biological membrane with no expenditure of energy.

Question 14

osmosis

Answer 14

The diffusion of free water across a selectively permeable membrane.

Question 15

tonicity

Answer 15

The ability of a solution surrounding a cell to cause that cell to gain or lose water.

Question 16

isotonic

Answer 16

Referring to a solution that, when surrounding a cell, causes no net movement of water into or out of the cell.

Question 17

hypertonic

Answer 17

Referring to a solution that, when surrounding a cell, will cause the cell to lose water.

Question 18

hypotonic

Answer 18

Referring to a solution that, when surrounding a cell, will cause the cell to take up water.

Question 19

osmoregulation

Answer 19

Regulation of solute concentrations and water balance by a cell or organism.

Question 20

turgid

Answer 20

Swollen or distended, as in plant cells. (A walled cell becomes turgid if it has a lower water potential than its surroundings, resulting in entry of water.)

Question 21

flaccid

Answer 21

Limp. Lacking turgor (stiffness or firmness), as in a plant cell in surroundings where there is a tendency for water to leave the cell. (A walled cell becomes flaccid if it has a higher water potential than its surroundings, resulting in the loss of water.)

Question 22

plasmolysis

Answer 22

A phenomenon in walled cells in which the cytoplasm shrivels and the plasma membrane pulls away from the cell wall; occurs when the cell loses water to a hypertonic environment.

Question 23

facilitated diffusion

Answer 23

The passage of molecules or ions down their electrochemical gradient across a biological membrane with the assistance of specific transmembrane transport proteins, requiring no energy expenditure.

Question 24

ion channels

Answer 24

A transmembrane protein channel that allows a specific ion to diffuse across the membrane down its concentration or electrochemical gradient.

Question 24

gated channels

Answer 24

A transmembrane protein channel that opens or closes in response to a particular stimulus.

Question 25

active transport

Answer 25

The movement of a substance across a cell membrane against its concentration or electrochemical gradient, mediated by specific transport proteins and requiring and expenditure of energy.

Question 26

sodium-potassium pump

Answer 26

A transport protein in the plasma membrane of animal cells that actively transports sodium out of the cell and potassium into the cell.

Question 27

membrane potential

Answer 27

The difference in electrical charge (voltage) across a cell’s plasma membrane due to the differential distribution of ions. Membrane potential affects the activity of excitable cells and the transmembrane movement of all charged substances.

Question 28

electrochemical gradient

Answer 28

The diffusion gradient of an ion, which is affected by both the concentration difference of an ion across a membrane (a chemical force) and the ion’s tendency to move relative to the membrane potential (an electrical force).

Question 29

electrogenic pump

Answer 29

An active transport protein that generates voltage across a membrane while pumping ions.

Question 30

proton pump

Answer 30

An active transport protein in a cell membrane that uses ATP to transport hydrogen ions out of a cell against their concentration gradient, generating a membrane potential in the process.

Question 31

cotransport

Answer 31

The coupling of “downhill” diffusion of one substance to the “uphill” transport of another against its own concentration gradient.

Question 32

exocytosis

Answer 32

The cellular secretion of biological molecules by the fusion of vesicles containing them with the plasma membrane.

Question 33

endocytosis

Answer 33

Cellular uptake of biological molecules and particulate matter via formation of vesicles from the plasma membrane.

Question 34

phagocytosis

Answer 34

A type of endocytosis in which large particulate substances or small organisms are taken up by a cell. It is carried out by some protists and by certain immune cells of animals (in mammals, mainly macrophages, neutrophils, and dendritic cells).

Question 35

pinocytosis

Answer 35

A type of endocytosis in which the cell ingests extracellular fluid and its dissolved solutes.

Question 36

receptor-mediated endocytosis

Answer 36

The movement of specific molecules into a cell by the inward budding of vesicles containing proteins with receptor sites specific to the molecules being taken in; enables a cell to acquire bulk quantities of specific substances.

Question 37

ligand

Answer 37

A molecule that binds specifically to another molecule, usually a larger one.