Chapter 7: Membrane Structure and Function

Question 1

selective permeability

Answer 1

some substances cross plasma membrane more easily

Question 2

amphipathic

Answer 2

hydrophilic region and hydrophobic region

Question 3

fluid mosaic model

Answer 3

membrane is a fluid structure with a mosaic of proteins (hydrophobic regions inside phospholipid bilayer with hydrophilic regions protruding out)

Question 4

freeze fracture

Answer 4

cell is frozen and fractured with a knife. splits the center of phospholipid bilayer into two separated layers. Each membrane protein goes wholly into one of the layers.

Question 5

membrane movement

Answer 5

membrane held together by hydrophobic interactions so most lipids (10^7 times per second) and some proteins shift laterally (not transversely).

Question 6

membrane fluidity

Answer 6

membrane solidifies as temperature decreases. fluidity depends on type of lipids (saturated solidifies more easily than unsaturated, which has kinks in tails)

Question 7

cholesterol

Answer 7

steroid that acts as membrane fluidity buffer. at high temps, restrains phospholipid movement. at low temps, prevent phospholipids from packing too close together.

Question 8

effects of membrane fluidity

Answer 8

solidified membrane has different permeability and enzymes may become inactive. too fluid membranes cannot support protein function.

Question 9

integral proteins

Answer 9

penetrate hydrophobic interior of lipid bilayer. majority are transmembrane. hydrophobic regions consist of 1+ stretches of nonpolar amino acids coiled into α helices.

Question 10

transmembrane protein

Answer 10

span the membrane

Question 11

peripheral proteins

Answer 11

loosely bound to surface of membrane (not embedded in lipid bilayer), often to exposed parts of integral proteins.

Question 12

membrane protein attachments

Answer 12

cytoplasmic side: attach to cytoskeleton
extracellular side: attach to ECM

Question 13

functions of membrane proteins

Answer 13

transport, enzymatic activity, signal transduction, cell-cell recognition, intercellular joining, attachment to cytoskeleton and ECM (coordinate extra and intra cellular changes)

Question 14

glycolipids

Answer 14

lipids with covalently bound carbohydrates

Question 15

glycoproteins

Answer 15

proteins with covalently bound carbohydrates

Question 16

HIV infection

Answer 16

HIV binds to CD4 receptor on cell and also needs to bind to CCR5 coreceptor in order to infect cell

Question 17

permeability of lipid bilayer

Answer 17

hydrophobic (nonpolar) molecules like O2, CO2, hydrocarbons, diffuse easily. hydrophilic (ions + polar) molecules diffuse slowly.

Question 18

transport proteins

Answer 18

help hydrophilic substances cross lipid membrane

Question 19

channel proteins

Answer 19

have hydrophilic channel that molecules/ions use as tunnel.

Question 20

aquaporins

Answer 20

channel proteins for water. (3 * 10^9 water molecules per second)

Question 21

carrier protein

Answer 21

bind to and change shape to shuttle molecule/ion across membrane

Question 22

diffusion

Answer 22

movement of molecule so it spreads out evenly

Question 23

concentration gradient

Answer 23

region along which density of substance increases/decreases

Question 24

passive transport

Answer 24

energy is not expended

Question 25

osmosis

Answer 25

diffusion of free water across selectively permeable membrane

Question 26

tonicity

Answer 26

ability of surrounding solution to gain/lose water. depends on partly on its concentration of nonpenetrating solutes

Question 27

isotonic

Answer 27

same tonicity. no net movement of water across plasma membrane

Question 28

hypertonic

Answer 28

more nonpenetrating solutes. cell loses water

Question 29

hypotonic

Answer 29

less nonpenetrating solutes. cell gains water

Question 30

osmoregulation

Answer 30

control of solute concentration and water balance

Question 31

turgor pressure

Answer 31

back pressure from rigid cell wall (plant cell) that opposes further water uptake

Question 32

turgid

Answer 32

very firm. needs hypotonic solution

Question 33

flaccid

Answer 33

limp. caused by hypertonic/isotonic solution

Question 34

plasmolysis

Answer 34

as plant cell loses water, plasma membrane shrinks away from cell wall. causes plant to wilt.

Question 35

facilitated diffusion

Answer 35

proteins assist with passive diffusion of impermeable substances

Question 36

ion channels

Answer 36

channel proteins that transport ions

Question 37

gated channels

Answer 37

channels that open or close in response to stimulus.

Question 38

active transport

Answer 38

expends energy. enables cells to maintain internal concentrations of solutes.

Question 39

cystinuria

Answer 39

absence of carrier protein that transports cysteine and other amino acids across membranes of kidney cells. causes painful kidney stones

Question 40

sodium potassium pump

Answer 40

exchanges Na+ for K+ across the plasma membrane.
Steps:
1. 3 Na+ bind, triggers phosphorylation by ATP (reduces affinity for Na+, increases affinity for K+)
2. Na+ released outside the cell. 2 K+ bind, causing phosphate group to be released
3. 2 K+ released inside the cell, and because the protein shape is restored the cycle repeats.

Question 41

voltage

Answer 41

electrical potential energy; separation of opposite charges

Question 42

membrane potential

Answer 42

voltage across a membrane. negative, because inside of the cell is more negative than the outside

Question 43

electrochemical gradient

Answer 43

combination of chemical force (concentration gradient) and electrical force (membrane potential) acting on an ion

Question 44

electrogenic pump

Answer 44

transport protein that generates voltage across a membrane
animals: sodium-potassium pump
plants, fungi, bacteria: proton pump

Question 45

proton pump

Answer 45

actively transports protons (H+) outside the cell

Question 46

cotransport

Answer 46

active transport driven by a concentration gradient.

Question 47

sucrose-H+ cotransporter

Answer 47

couples downhill diffusion of H+ into a plant cell to active transport of sucrose into the cell

Question 48

exocytosis

Answer 48

transport vesicles fuse with plasma membrane to secrete molecules outside the cell

Question 49

endocytosis

Answer 49

cell takes in substances by forming new vesicles from plasma membrane

Question 50

Low-density lipoproteins

Answer 50

complex of lipids and proteins that transport cholesterol. binds to LDL receptors on plasma membranes and enter cell through endocytosis

Question 51

familial hypercholesterolemia

Answer 51

high level of cholesterol in the blood because of defective LDL receptors

Question 52

phagocytosis

Answer 52

cell engulfs particle by wrapping pseudopodia around it and forming a food vacuole (which fuses with a lysosome)

Question 53

pinocytosis

Answer 53

cell “gulps” droplets of extracellular fluid (with molecules) into vesicles. nonspecific transport

Question 54

receptor-mediated endocytosis

Answer 54

allows for bulk transport of specific substances
1. proteins with receptor sites exposed to extracellular fluid are embedded in the plasma membrane.
2. Ligands (for receptors) bind
3. Receptor proteins cluster in coated pits (lined with fuzzy proteins on cytoplasmic side)
4. after receptors are emptied, the vesicle returns them to plasma membrane