lecture 18

Question 1

3 membrane characteristics

Answer 1

involved in receiving info, import and export of molecules, motility (movement)

selective barriers

external and internal (ER, golgi, nucleus)

Question 2

Hydrophilic molecules form

Answer 2

H bonds with water molecules

Question 3

Hydrophobic molecules can’t..

Answer 3

form H bonds

Question 4

predominant lipids in the cell membrane

Answer 4

phospholipids

Question 5

phospholipids have

Answer 5

a phosphate head
two hydrophobic tails

Question 6

ampiphatic

Answer 6

one part hydrophobic, one part hydrophillic

Question 7

lipid bilayers are…

Answer 7

self-sealing

Question 8

4 characteristics of a lipid bilayer

Answer 8

bilayers eliminate free edges to hide the hydrophobic tails from water

spontaneously form liposomes in the water

bend and adapt to changes in membrane structure

lipids can move laterally but not vertically

Question 9

fluidity

Answer 9

the ease with which lipid molecules move in the plane of the bilayer

Question 10

2 properties of the hydrocarbon chain that affect fluidity

Answer 10

1. length of chain:
   - shorter chain= less tail-tail interaction, increased fluidity
   - longer chain= decreased fluidity
2. number of double bonds:
   - saturated= no double bonds, increased fluidity
   - unsaturated= double bonds, kink in the chain, decreased fluidity

Question 11

saturated hydrocarbon chain means

Answer 11

fully saturated w hydrogens, no double bonds, more fluid

Question 12

unsaturated hydrocarbon chains means

Answer 12

at least one double bond, creates a kink in the chain making it less fluid

Question 13

what would you do to increase membrane fluidity at colder temp?

Answer 13

increase the number of double bonds in the carbon chain

Question 14

3 characteristics of cholesterol

Answer 14

• Short, rigid lipid molecules that fill the space (caused by kinks in hydrocarbon tail) between neighbouring phospholipids
• Can stiffen the membrane
• Increases melting point of the membrane

Question 15

how is the membrane assembled? (where are new phospholipids made?)

Answer 15

new phospholipids are made on the cytosolic side of the ER.

they remain on that monolayer unless they are transferred to the other layer by a protein

Question 16

What causes the redistribution of phospholipids?

Answer 16

scramblases and flippases

redistribution causes asymmetric distribution of phospholipids

Question 17

scramblases

Answer 17

randomly move phospholipids from one monolayer to the other

Question 18

flippases

Answer 18

the golgi membrane has flippases which remove specific phospholipids from one side to the other

Question 19

which way are cytosolic proteins facing when being transported?

Answer 19

they remain facing the cytosol

Question 20

name 7 membrane proteins

Answer 20

transmembrane
monolayer-associated alpha helix
lipid linked
protein attached
detergents
integral membrane proteins
peripheral membrane proteins

Question 21

transmembrane proteins

Answer 21

extend through the bilayer

Question 22

monolayer associated alpha helix proteins

Answer 22

amphipathic alpha helix embedded in a monolayer

Question 23

lipid linked protein

Answer 23

attached to the membrane through 1+ covalently linked groups

Question 24

protein attached proteins

Answer 24

attached to membrane indirectly by association with a membrane protein

Question 25

detergents

Answer 25

small amphipathic molecules w only one hydrophobic tail (they form micelles)

Question 26

integral membrane proteins

Answer 26

need detergents to be removed from the membrane

Question 27

peripheral membrane proteins

Answer 27

can be removed by gentler procedures

Question 28

why do detergents form micelles, and phospholipids form liposomes in water?

Answer 28

detergents are wedge shaped phospholipids are cylindrical

Question 29

polypeptide chains cross the lipid bilayer with an

Answer 29

alpha helix

Question 30

single pass

Answer 30

only crosses the membrane one

Question 31

multipass

Answer 31

crosses the membrane multiple times

Question 32

beta sheets can cross the membrane as a

Answer 32

beta barrel

Question 33

cell cortex=

Answer 33

meshwork of fibrous proteins on the cytosolic side of the membrane animal cells have a cell cortex (rather than a cell wall like plants)

Question 34

lipids can move freely in the plane unless...

Answer 34

restricted by a membrane domain

Question 35

tight junctions prevent

Answer 35

diffusion of proteins to other sides of the cell

Question 36

glycoproteins

Answer 36

proteins w short chains of sugar

Question 37

proteoglycans

Answer 37

proteins w long chains of sugar

Question 38

glycocalyx

Answer 38

carbohydrate later, located outside the plasma membrane - protects cell (slimy) from mechanical damage - cell-cell recognition and adhesion