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

Components of the Phospholipid Bilayer

Answer 2

Phospholipids 
Integral proteins 
Transmembrane proteins 
Peripheral proteins 
Glycolipid 
Cholesterol

Question 3

Integral Proteins

Answer 3

A transmembrane protein with hydrophobic regions that extend into and often completely span the hydrophobic interior of the membrane with hydrophilic regions in contact with the aqueous solution on one or both sides of the membrane

Question 4

Transmembrane proteins

Answer 4

A type of integral protein that spans the entire membrane

Question 5

Peripheral protein

Answer 5

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

Question 6

Glycolipid

Answer 6

A lipid with one or more covalently attached carbohydrates

A protein with one or more covalently attached carbohydrates

Question 7

Cholesterol

Answer 7

Functions as a fluidity buffer for animal cells

- the double bonds in cholesterol aid the bilayer in resisting changes in temperature and as a result the fluidity.

Question 8

Selective permeability

Answer 8

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

Depends on both the discriminating barrier of the lipid bilayer and the specific transport proteins built into the membrane

Question 9

Permeability of the bilayer

Answer 9

Non polar molecules - Since they are hydrophobic they can cross the lipid bilayer easily, without the aid of membrane proteins.

Polar molecules - since they are hydrophilic, they cross very slowly. Charged atoms or molecules are even less likely to penetrate the hydrophobic interior

Proteins that are built into the membrane regulate the transport of polar and charged molecules.

Question 10

Transport proteins

Answer 10

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

Question 11

Channel proteins

Answer 11

Hydrophilic Channel that certain molecules or ions use as a tunnel through the membrane

Question 12

Aquaporin

Answer 12

A Channel protein that specifically facilitates osmosis, the diffusion of free water across the membrane

Question 13

Carrier proteins

Answer 13

Hold onto their passengers and change shape in a way that shuttles them across the membrane

Question 14

Diffusion

Answer 14

The random thermal motion of particles of liquids, gases or solids. In the presence of a concentrated or electrochemical gradient, diffusion results in the net movement of a substance from a region where it is more concentrated to a region where it is less concentrated

Question 15

Concentration gradient

Answer 15

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

Question 16

Passive transport

Answer 16

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

Question 17

Osmosis

Answer 17

The diffusion of free water across a selectively permeable membrane

Question 18

Tonicity

Answer 18

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

Question 19

Isotonic

Answer 19

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

Question 20

Hypertonic

Answer 20

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

Question 21

Hypotonic

Answer 21

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

Question 22

Osmoregulation

Answer 22

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

Question 23

Turgid

Answer 23

Swollen or distended, as in plant cells in surrounding where there is a tendency for water to enter the cell

Question 24

Flaccid

Answer 24

Limp. As in a plant cell in surrounding where there is a tendency for water to leave the cell

Question 25

Plasmolysis

Answer 25

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 26

Facilitated diffusion

Answer 26

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 27

Ion Channel

Answer 27

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

Question 28

Gated Channel

Answer 28

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

Question 29

Active Transport

Answer 29

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

Question 30

Membrane potential

Answer 30

The difference in electrical charges 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 31

Electrochemical gradient

Answer 31

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

Question 32

Electrogenic Pump

Answer 32

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

Question 33

Sodium Potassium Pump

Answer 33

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

Question 34

Proton Pump

Answer 34

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 35

Cotransport

Answer 35

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

Question 36

Exocytosis

Answer 36

the cellular segregation of biological molecules by the fusion of vesicles, containing them within the plasma membrane.

Question 37

Endocytosis

Answer 37

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

Question 38

Phagocytosis

Answer 38

Cell engulfs a particle by packing it within a membranous sac and the particle will be digested after the food vacuole fuses with a lysosome

Question 39

Pinocytosis

Answer 39

Gulps droplets of extracellular fluid into tiny vesicles

Non specific for the substances it transports

Question 40

Receptor mediated endocytosis

Answer 40

A type of pinocytosis that allows for the transport of specific substances through binding to receptors