CHAPTER 6

Question 1

fluid mosaic model

Answer 1

describes the general structure of biological membranes

Question 2

phospholipids

Answer 2

form bilayer; polar, hydrophilic heads with non polar, hydrophobic tails; vary in fatty acid chain, length, degree of unsaturation, and phosphate groups

Question 3

cholesterol

Answer 3

important for membrane integrity and modulates fluidity

Question 4

What are the three types of membrane proteins?

Answer 4

INTEGRAL
PERIPHERAL
ANCHORED

Question 5

glycolipids

Answer 5

carbohydrate + lipid

Question 6

glycoproteins

Answer 6

carbohydrate (oligosaccharide) + protein; proteoglycans have a higher percentage of carbohydrates

Question 7

cell junctions

Answer 7

specialized structures that hold cells together
TIGHT - help ensure directional movement of materials
DESMOSOMES - “spot welds”
GAP - allow communication

Question 8

integrin

Answer 8

transmembrane protein that binds to the matrix outside epithelial cells and to actin filaments inside the cells; binding is noncovalent and reversible

Question 9

selective permeability

Answer 9

membranes allow some substances that can pass through, but not others

Question 10

passive transport

Answer 10

no energy input required (diffusion)

Question 11

active transport

Answer 11

energy required

Question 12

concentration gradient

Answer 12

solutes going from high concentration to low concentration

Question 13

diffusion

Answer 13

process of random movement toward equilibrium; net movement is directional until equilibrium is reached; net movement from regions of greater concentration to regions of lesser concentration

Question 14

What does diffusion rate depend on?

Answer 14

-SIZE and MASS of the molecules or ions
-TEMPERATURE of the solution
-DENSITY of the solution
-CONCENTRATION GRADIENT
-AREA and DISTANCE

Question 15

simple diffusion

Answer 15

small molecules pass through the lipid bilayer; lipid-soluble molecules can diffuse across the membrane while electrically charged and polar molecules can’t pass through easily

Question 16

osmosis

Answer 16

diffusion of water; depends on the relative concentrations of water molecules

Question 17

isotonic

Answer 17

equal solute concentrations

Question 18

hypertonic

Answer 18

higher solute concentrations

Question 19

hypotonic

Answer 19

lower solute concentrations

Question 20

turgor pressure

Answer 20

when plant cells with rigid cell walls build up internal pressure that keeps more water from entering

Question 21

facilitated diffusion

Answer 21

polar and charged molecules diffuse with concentration gradients, but facilitated by protein channels or carriers

Question 22

channel proteins

Answer 22

integral membrane proteins that form a tunnel

Question 23

carrier proteins

Answer 23

membrane proteins that bind some substances and speed their diffusion through the bilayer; transport polar molecules, such as glucose, across membranes in both directions

Question 24

ion channels

Answer 24

channel proteins with hydrophilic pores; most are gated (can be closed or open to ion passage); gate open when the protein is stimulated to change shape by a chemical signal (ligand) or electrical charge difference (voltage-gated)

Question 25

aquaporins

Answer 25

special channels that help water cross membranes; ions are excluded; first identified by injecting them into a frog oocyte

Question 26

What does the rate of facilitated diffusion depend on?

Answer 26

-CONCENTRATION GRADIENT
-NUMBER of CARRIER PROTEINS in the CELL MEMBRANE

Question 27

active transport

Answer 27

moves substances against a concentration and/or electrical gradient; requires energy; the energy source is often adenosine triphosphate (ATP); is directional; it involves three kinds of proteins

Question 28

uniporter

Answer 28

moves one substance in one direction

Question 29

symporter

Answer 29

moves two substances in one direction

Question 30

antiporter

Answer 30

moves two substances in opposite directions

Question 31

primary active transport

Answer 31

requires direct hydrolysis of ATP; the sodium-potassium (Na+ - K+) pump is an integral membrane glycoprotein (an antiporter):
- brings two K+ ions into the cell and exports three Na+ ions

Question 32

secondary active transport

Answer 32

energy comes from an ion concentration gradient that is established by primary active transport; once the Na+ - K+ pump establishes a concentration gradient of Na+, passive diffusion of some Na+ back into the cell provides energy for the transport of glucose into the cell against its concentration gradient.

Question 33

How can macromolecules cross the membrane?

Answer 33

they can be taken in or secreted by means of membrane vesicles

Question 34

endocytosis

Answer 34

brings molecules and cells into a eukaryotic cell; the cell membrane folds inward, or invaginates, around the material, forming a vesicle

Question 35

phagocytosis

Answer 35

molecules or entire cells are engulfed; some protists feed in this way; some white blood cells engulf foreign substances in this way; a food vacuole or phagosome forms, which fuses with a lysosome where the contents are digested

Question 36

pinocytosis

Answer 36

a vesicle forms to bring small dissolved substances or fluids into a cell; vesicles are much smaller than in phagocytosis; is constant in endothelial (capillary) cells

Question 37

receptor mediated endocytosis

Answer 37

is highly specific; macromolecules to be moved bind to receptor proteins (integral membrane proteins located at specific sites on the cell membrane); sites are also coated with proteins such as clathrin on the inside

Question 38

exocytosis

Answer 38

materials packaged in vesicles (e.g., digestive enzymes and neurotransmitters) are secreted from a cell when the vesicle membrane fuses with the cell membrane; or, the vesicle touches the cell membrane and a pore forms, releasing the vesicle’s contents; no membrane fusion