Exam 1: Chapter 4

Question 1

membrane functions

Answer 1

1. compartmentalization
2. providing a selective permeable barrier
3. transporting solutes
4. responding to external signals
5. intercellular interaction
6. locus for biochemical activities
7. energy transduction

Question 2

structure and function of the plasma membrane: lipids

Answer 2

• major component

- amphipathic molecules (have both polar and non-polar ends)

Question 3

osmium dye stains

Answer 3

polar head groups only

Question 4

membrane permeability not strictly dependent on

Answer 4

lipid solubility

Question 5

1960’s Singer and Nicholson: fluid mosaic model said

Answer 5

membranes also contain proteins and carbohydrates and are dynamic structures

Question 6

lipid bilayer

Answer 6

• provides fluid structural framework
• has ability to self-assemble in aqueous solution
• contributes to membrane fluidity and flexibility
• form vast interconnected membrane networks

Question 7

protein

Answer 7

carry out most of the specific functions of membrane

Question 8

carbohydrate

Answer 8

cell/cell interactions, protein anchoring, folding and function

Question 9

liposome

Answer 9

self-assembled fluid filled membrane vesicle formed in vitro from phospholipids in aqueous solution
-serves as drug delivery vehicle

Question 10

cholesterol

Answer 10

• smaller than most lipids
• less amphipathic hydrophilic -OH group towards exterior hydrophobic tail in lipid bilayer
• flat and rigid rings prevent close packing of lipids, -increase fluidity at low concentration - decrease fluidity at high concentration

Question 11

high cholesterol reduces lateral shift of surrounding phospholipid head groups on outer leaflet

Answer 11

stiffens and reduces permeability

Question 12

cholesterol-rich lipid rafts

Answer 12

• regions of high cholesterol have low fluidity and lateral shift
• sites of GPI (glycolipid)-anchored signaling proteins
• surrounded by *more fluid membrane (lower cholesterol)
• important for cell signaling

Question 13

plasma membrane of neuronal axon-myelin sheath

Answer 13

• multiple layers
• high cholesterol content
• low protein to lipid ratio
• stiff, non-fluid, impermeable structure insulates cell

Question 14

protein dynamics in membranes

Answer 14

technique used to demonstrate dynamic movement of proteins in membranes

• -cell fusion: spread of labeled protein throughout membrane of fused cell
• -FRAP: fluorescence recovery after photobleaching

Question 15

FRAP

Answer 15

method used to monitor dynamics of proteins in many cellular compartments-not just membranes

• short FRAP time: very dynamic
• long FRAP time: very static

Question 16

Membrane proteins: integral

Answer 16

penetrate through lipid bilayer

Question 17

Membrane proteins: peripheral

Answer 17

outside membrane but associated with cytoplasmic side through noncovalent bonds

Question 18

Membrane proteins: lipid-anchored

Answer 18

outside membrane but associated with either extracelluar or cytoplasmic side through covalent bond

Question 19

immunoelectron microscopy and freeze fracture used to

Answer 19

determine distribution of membrane proteins in lipid bilayer

Question 20

freeze fracture technique

Answer 20

peel lipid bilayer apart to examine protein distribution in lipid bilayer

Question 21

non mediated passive diffusion - osmosis

Answer 21

membranes are semipermeable

• H2O moves through them more rapidly than dissolved ions or small polarsolutes
• H2O moves form a region of higher H2O to a region of lower [H2O] (higher [solute])

Question 22

hypotonic

Answer 22

water flows from water into cell

Question 23

hypertonic

Answer 23

water flows from cell to water

Question 24

isotonic

Answer 24

no net flow

Question 25

passive transport: transporter (carrier) mediated

Answer 25

move molecules from region of high concentration to region of low concentration deltaG<0

Question 26

two methods of gating:

Answer 26

ligand-gated: conformation depends on concentration of specific ligand
voltage-gated: conformation depends on charge across membrane

Question 27

Transporter facilitated diffusion: ligand gated
Glucose transporter (GLUT4)

Answer 27

• localized on plasma membrane in response to insulin
• solute (glucose) binds to transporter on high glucose side of membrane
• conformational change triggered
• solute free to diffuse to low conc.
• no energy required
• works equally in both directions
• mutant forms associated with diabetes type 2

Question 28

Transporter facilitated diffusion: voltage gated

Voltage gated K+ channel

Answer 28

• 6 membrane spanning segments -S4 helix regulates opening - (+) charged residues distributed throughout S4 act as voltage (charge) sensor - depolarization of membrane generates electric current through (+) charged residues
• S4 helix moves, allowing K+ to freely flow out

Question 29

ions flow through ion channels

Answer 29

voltage-gated K+ channel

Question 30

Nerve impulse

Answer 30

1. resting potential (Na+/K+-ATPase establishes ion gradient)
2. Depolarization (Na+ flows in)
3. re polarization (K+ flows out)