Lecture 10 Membranes

Question 1

lipid bilayer

Answer 1

Th e membrane is made of proteins (50%) and lipids (50%)
Lipids are amphiphilic i.e. they have
-a polar part (hydrophylic head) and
-a non-polar part (hydrophobic tail, 14-24 carbons, saturated or unsaturated, depending on the fatty acid)

Question 2

phospholipids

Answer 2

Most lipids in the membrane are phospholipids:
- phosphoglycerides (based on glycerol)
- sphingolipids (based on sphingosine)
Most lipids have no net charge. Phospatidylserine has a net negative charge

Question 3

cholesterol

Answer 3

Eukaryal membranes contain large amounts of cholesterol (sterol) which modulates the permeability and the packing of the membrane. By decreasing the mobility of the first few –CH 2 groups it structures the bilayer locally and makes is less prone to deformation.
-> stiffer, thicker membrane

Question 4

unsaturated/saturated fatty acid

Answer 4

unsaturated:
- hydrocarbon chain with cis-double bounds
- eg oil
saturated:
- hydracarbon chain
- eg butter

Question 5

Water molecules arrange in ordered … structures around … molecules

Answer 5

cage-like

hydrophobic

Question 6

micelle

Answer 6

p

Question 7

liposomes

Answer 7

Entropy drives minimizing the number of water molecules in ordered cage-like structures, meaning that the exposed hydrophobic surfaces get minimized

Question 8

Molecular motions in the lipid bilayer

Answer 8

lateral diffusion
rotation
flexion
flip-flop (rarely occurs)

Question 9

asymmetrical membrane

Answer 9

p

Question 10

proteins in membranes

Answer 10

Biological membranes contain various proteins, that can be associated to the membrane in these different ways (7)

Question 11

Disulfide bonds are normally not found in the reducing environment of the …
Same goes for glycosylated proteins

Answer 11

cytosol

Question 12

FRAP

Answer 12

Fluorescence recovery after photobleaching

FRAP: measuring the speed of lateral diffusion of a given protein (protein tagged with GFP)

Question 13

limitation of lateral diffusion

Answer 13

When needed, cells can limit the lateral diffusion of membrane components
proteins stick together -> islands of proteins block the motion

Question 14

Proteins can “bend” membranes, how?

Answer 14

• by inserting hydrophobic domains
• by binding a curved protein surface to the lipid head groups
• By specifically binding larger lipid head groups

Question 15

How to get molecules across the membrane?

Answer 15

transporters and channels
easy -> hardest:
1. hydrophobic molecules
2. small uncharged polar molecules 
3. large uncharged polar molecules 
4. ions

Question 16

passive/active transport

Answer 16

passive:

• simple diffusion
• channel-mediated
• transporter-mediated

active:

• coupled transporter
• ATP-driven pump
• light driven pump

Question 17

ATP-driven active transport (pumps): 3 classes

Answer 17

P-type: ion pump that undergoes phosphorylation
ABC-type: transport small molecules not ions
F-type/V-type: ATP-synthases, made of several different subunits, found in bacteria, mitochondria and chloroplasts, use the gradient of protons to synthesize ATP. Can also work in reverse and hydrolyze ATP in order to pump protons (V-type).

Question 18

Gram+ (G+) and Gram- (G-) bacteria

Answer 18

G +: cell membrane and a thick peptidoglycan

G-: cell membrane, thin peptidoglycan and outer membrane with porins

Question 19

Compartments of the Eukaryal cell are made of membranes

Answer 19

eg ER, Golgi apparatis, mithocondria

Question 20

protein trafficking

Answer 20

Gated transport
Transmembrane transport
Vesicular transport

Question 21

How proteins end up in the right place?

Answer 21

Signal sequences (like cinema tickets)

Question 22

How do proteins get into the ER?

Answer 22

ribosomes attaching to the ER surface

translocators, signal sequences

Question 23

exocytosis/endocytosis

Answer 23

p

Question 24

Properly folded proteins leave the … in a … and go towards …

Answer 24

ER
vesicle
Golgi

Question 25

Golgi apparatus

Answer 25

sorting ->

• lysosome, eller
• plasma membrane, eller
• secretory vesicle

Question 26

The lysosome

Answer 26

A lysosome is a membrane-bound cell organelle that contains digestive enzymes. Lysosomes are involved with various cell processes. They break down excess or worn-out cell parts.

Question 27

Phagocytic cells

Answer 27

Phagocytic cells can engulf and degrade entire cells