Chapter 10: Membrane Structure

Question 1

plasma membrane

Answer 1

encloses cell defines its boundaries maintains essential differences between cytosol and extracellular environment

Question 2

receptors

Answer 2

proteins on plasma membrane that sense external signals transfer information (not molecules) across the membrane

Question 3

All biological membranes have a…

Answer 3

general common structure

Question 4

general structure of biological membranes

Answer 4

very thin film of lipid and protein molecules held together mainly by noncovalent interactions

Question 5

cell membrane features

Answer 5

dynamic, fluid structures molecules move about in plane of the membrane lipid molecules are a continuous double layer

Question 6

lipid bilayer

Answer 6

provides fluid structure of the membrane and is relatively impermeable to passage of water-soluble molecules

Question 7

membrane proteins

Answer 7

span the lipid bilayer and mediate transport of molecules across it and catalysis of ATP synthesis

Question 8

how to view lipid bilayer

Answer 8

electron microscopy

Question 9

bilayer assembly

Answer 9

lipids spontaneously assemble even under simple artificial conditions

Question 10

amphiphilic

Answer 10

have a hydrophilic (polar) and hydrophobic (nonpolar) end EX: all lipids in cell membranes

Question 11

phospholipids

Answer 11

most abundant membrane lipids polar head with phosphate group and 2 hydrophobic carbon tails fatty acids in animal, plant, and bacterial cells one tail is unsaturated (one or more cis double bonds) and the other is usually saturated

Question 12

phosphoglycerides

Answer 12

3-carbon glycerol backbone 2 long chain fatty acids are linked through ester bonds to adjacent carbon atoms of glycerol 3rd carbon atom of glycerol is attached to a phosphate group (linked to several head groups)

Question 13

phospholipid structure image

Answer 13

Question 14

sphingolipid

Answer 14

phospholipid but with sphingosine rather than glycerol

Question 15

sphingosine

Answer 15

long acyl chain with amino group (NH2) and 2 hydroxyl (OH)

Question 16

major phospholipids in cell membrane

Answer 16

phosphatidylethanolamine, phosphatidylserine, phosphatidylcholine, sphingomyelin, sphingosine

Question 17

cholesterol

Answer 17

found in large amounts in eukaryotic plasma membranes

a sterol

rigid ring structure attached to polar hydroxyl group and short nonpolar hydrocarbon chain

hydroxyl = near polar head of adjacent phospholipids

Question 18

phospholipids form bilayers

Answer 18

spontaneous!

hydrophobic tails inside, hydrophilic heads exposed on outside

increases free energy (cage structure is more ordered than surrounding water)

Question 19

2 ways to form phospholipids

Answer 19

1) spherical micelles (tails inward)
2) double-layered sheets (bilayers) hydrophobic tails sanwiched between hydrophilic head groups

Question 20

self-sealing property

Answer 20

same force that drives phospholipids to form bilayers also self-seals them

a small tear in the bilayer would create a free edge with water (energetically unfavorable) so lipids rearrange spontaneously to eliminate the free edge

bilayer seals in on itself to prevent having edges

Question 21

liposomes

Answer 21

spherical vessels that make artificial lipid bilayer

Question 22

flip-flop

Answer 22

phopsholipid moleci;es in synthetic bilayers very raraely migrate from the monolayer (leaflet) on one side to that on the other

takes hours (but cholesterol can do so rapidly)

Question 23

rapid lateral diffusion

Answer 23

lipids rapidly exchange places with their neighbors within a monolayer

gives rise to rapid lateral diffusion

Question 24

individual lipid molecule rotation

Answer 24

very rapidly rotate along long axis

have flexible hydrocarbon chains

Question 25

manufacturing phospholipids

Answer 25

only occurs in one monolayer of a membrane

mainly in cytosolic monolayer of endoplasmic reticulum membrane

only made bc newly made molecules can migrate quickly to noncytosolic monolayer (creates bilayer)

Question 26

phospholipid translocators (aka flippases)

Answer 26

catalyze rapid flip-flop of phospholipids from one monolayer to the other

Question 27

liposomes fusion

Answer 27

liposomes DO NOT fuse spontaneously with one another when suspended in water

this is bc polar lipid head groups bind water molecules that need to be displaced for the bilaayers of 2 different liposomes to fuse

hydration shell is keeping them apart

Question 28

hydration shell

Answer 28

insulates internal membranes in euk cell and prevents their uncontrolled fusion

maintains compartmental integrity of membrane-enclosed organelles

Question 29

cell membrane fusion events

Answer 29

catalyzed by tightly regulated fusion proteins

they force appropriate membranes into tight proximity, squeezing out the water layer that keeps the bilayers apart

Question 30

unsaturated vs saturated organization

Answer 30

Question 31

phase transition

Answer 31

at a certain temperature, phospholipid changes from liquid to 2-D rigid crystalline (or gel) state

this temp is lower (membrane is more difficult to freeze) if HC chains are short or have double bonds

Question 32

shorter chain length causes bonds to…

Answer 32

reduces tendency of hydrocarbon tails to interact with one another (in both the same and opposite monolayer)

cis double bonds produce kinks in the chains that make them more difficult to pack together –> membrane stays fluid at lower temps

Question 33

organisms whose temp fluctuates with their environment

Answer 33

adjust FA composition of membrane lipids to maintain constant fluidity

EX: temp falls, cells synthesize FA with more cis-double bonds (avoids decrease in bilayer fluidity that would otherwise come from temp drop)