Membranes

Question 1

What are 4 functions of membranes?

Answer 1

Separate the outside from inside
Control solute transport in or out of cells
Organize complex enzymatic processes
Control cell adhesion and communication

Question 2

What are the 5 properties of membranes?

Answer 2

Consist of lipids and proteins, with carbohydrates on the outside
Very thin 
Flexible 
Self-sealing and dynamic
Held together by non covalent forces

Question 3

What traits will membranes with low fluidity have?

Answer 3

Phospholipids will be saturated and stretched out. Both lateral and transverse movements will be low

Question 4

What traits will membranes with high fluidity have?

Answer 4

Some phospholipids will be unsaturated and heterogenous. Lateral movements are rapid but transverse movements are still slow

Question 5

Why is fluidity essential for membrane function?

Answer 5

Vesicle exo and endocytosis, endosomes and lysosomes, viral infection, fertilization, vacuoles, cell division

Question 6

How can cells change their membrane fluidity?

Answer 6

Change the composition

Question 7

What are the two types of movements that lipids in the membrane can do?

Answer 7

Flip-flop diffusion and lateral diffusion

Question 8

How do you study lipid movements?

Answer 8

FRAP: fluorescence recovery after photobleaching

Question 9

How does FRAP work?

Answer 9

All the heads of lipids on the outer membrane are labelled with a fluorescent dye, then one spot of the membrane is zapped with a powerful laser which bleaches it. Then you observe that spot and watch how long it takes for the surrounding lipids to diffuse into the spot

Question 10

What are the 3 transporters that catalyze movement of lipids from one leaflet to the other?

Answer 10

Scramblase, flippase and floppase

Question 11

What does scramblase do?

Answer 11

Equilibrates lipids on either side of the membrane, which is spontaneous

Question 12

What does flippase do?

Answer 12

Moves phosphotidylserine and phosphotidylethyl from the outer leaflet to the inner leaflet. Active transport

Question 13

What does floppase do?

Answer 13

Moves phospholipids from the inner leaflet to the outer leaflet. Active transport

Question 14

Which of scramblase, flippase, and floppase uses passive transport?

Answer 14

Scramblase. The other two are active

Question 15

What is single particle tracking?

Answer 15

A single lipid molecule is labelled and its movement is followed by fluorescence microscopy

Question 16

Why is lateral motion of lipids in the membrane constrained?

Answer 16

Cytoskeleton borders, membrane proteins, membrane nonhomogeneiety

Question 17

What are lipid rafts?

Answer 17

Microdomains in the membrane made of cholesterol and glycosphingolipids

Question 18

Why do glycosphingolipids make up limit rafts and not glycerophospholipids?

Answer 18

The glycosphingolipids tend to have fully extended tails and will stick with the cholesterol, which favours the fully extended tails. Glycerophospholipids have unsaturated tails that are liquid disordered and shorter

Question 19

How can we see lipid rafts?

Answer 19

Atomic force microscopy

Question 20

How does atomic force microscopy work?

Answer 20

Has a probe that moves along the surface features of membrane, and lipid rafts are thicker than the surrounding glycerophospholipid sea, and can be distinguished from the surroundings

Question 21

What do lipid rafts do?

Answer 21

Segregate membrane proteins and confined favourable protein interactions to a certain area of the membrane