Chapter 7 Terms

Question 1

Selective permeability

Answer 1

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

Question 2

amphipathic

Answer 2

having both a hydrophilic region and a hydrophobic region

Question 3

fluid mosaic model

Answer 3

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 phospolipids

Question 4

Integral proteins

Answer 4

a transmembrane protein with hydrophobic regions that extend into and 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 5

Peripheral proteins

Answer 5

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 6

Functions of membrane proteins

Answer 6

• Transport
• Enzymatic activity
• Signal transduction
• Cell-cell recognition
• Intercellular joining
• Attachment to the cytoskeleton and extracellular matrix (ECM)

Question 7

Transport

Answer 7

a protein that spans the membrane may provide a hydrophilic channel across the membrane that is selective for a particular solute; other transport proteins shuttle a substance from one side to the other by changing shape. Some of these proteins hydrolyze ATP as an energy source to actively pump substances across the membrane

Question 8

Enzymatic activity

Answer 8

a protein built into the membrane may be an enzyme with its active site exposed to substances in the adjacent solution. In some cases, several enzymes in a membrane are organized as a team that carries out sequential steps o of a metabolic pathway

Question 9

Signal Transduction

Answer 9

a membrane protein (receptor) may have a binding site with a specific shape that fits the shape of a chemical messenger, such as a hormone. The external messenger (signaling molecule) may cause the protein to shape, allowing it to relay message to the inside of the cell, usually by binding to a cytoplasmic protein

Question 10

Cell-cell recognition

Answer 10

Some glycoproteins serve as identification tags that are specifically recognized by membrane proteins of other cells. This type of cell-cell binding is usually short-lived compared to that shown.

Question 11

Intercellular joining

Answer 11

Membrane proteins of adjacent cells may hook together in various kinds of junctions, such as gap junctions or tight junctions. This type of binding is more long-lasting.

Question 12

Attachment to the cytoskeleton and extracellular matrix (ECM)

Answer 12

Microfilaments or other elements of the cytoskeleton may be noncovalently bound to membrane proteins, a function that helps maintain cell shape and stabilizes the location of certain membrane proteins. Proteins that can bind to ECM molecules can coordinate extracellular and intracellular changes.

Question 13

Glycolipids

Answer 13

a lipid with one or more covalently attached carbohydrates

Question 14

Glycoproteins

Answer 14

a protein with one or more covalently attached carbohydrates

Question 15

Transport protein

Answer 15

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

Question 16

Aquaporin

Answer 16

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 17

Diffusion

Answer 17

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 18

Concentration gradient

Answer 18

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

Question 19

Passive transport

Answer 19

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

Question 20

Osmosis

Answer 20

The diffusion of free water across a selectively permeable membrane

Question 21

Tonicity

Answer 21

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

Question 22

Isotonic

Answer 22

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

Question 23

Hypertonic

Answer 23

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

Question 24

Hypotonic

Answer 24

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

Question 25

Osmoregulation

Answer 25

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

Question 26

Turgid

Answer 26

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 27

Flaccid

Answer 27

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 28

Plasmolysis

Answer 28

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 29

Facilitated diffusion

Answer 29

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 30

Ion channel

Answer 30

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

Question 31

Gated channel

Answer 31

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

Question 32

Active transport

Answer 32

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

Question 33

Sodium-potassium pump

Answer 33

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

Question 34

Membrane potential

Answer 34

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 35

Electrochemical gradient

Answer 35

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 36

Electrogenic pump

Answer 36

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

Question 37

Proton pump

Answer 37

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 38

Cotransport

Answer 38

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

Question 39

Exocytosis

Answer 39

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

Question 40

Endocytosis

Answer 40

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

Question 41

Ligand

Answer 41

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

Question 42

Three types of endocytosis

Answer 42

• Phagocytosis
• Pinocytosis
• Receptor-mediated endocytosis

Question 43

Phagocytosis

Answer 43

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 44

Pinocytosis

Answer 44

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

Question 45

Receptor-mediated endocytosis

Answer 45

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 on; enables a cell to acquire bulk quantities of specific substances