Membrane Structure and Function

Question 1

What are the two possible backbone structures of phospholipids?

Answer 1

Glycerol and Sphingosine

Glycerol: The 3OH groups of glycerol are sites for side chain attachments

Sphingosine: Usually O-linked to a charged group and amide-linked to an acyl group, such as a fatty acid

Question 2

Which of these cannot diffuse through the membrane?
A. Charged molecules
B. Water
C. Estrogen
D. They can all diffuse through the membrane

Answer 2

A. Charged molecules

CAN DIFFUSE: O2, N2, H2O, and CO2, Hydrophobic compounds

CANNOT DIFFUSE: Charged molecules, glycine and other amino acids

Question 3

How are lipid components distributed throughout the membrane?

Answer 3

Asymmetrically

Question 4

PIP2 is cleaved by what enzyme to form second messengers IP3 and DAG?

Answer 4

Phospholipase C

Question 5

What happens when lipids are dispersed in water?

Answer 5

They naturally form vesicles

Question 6

What are liposomes?

Answer 6

Artificially prepared vesicle composed of a lipid bilayer. Liposomes can be used to administer and transport nutrients and pharmaceutical drugs in the body

Question 7

Proteins have numerous localizations in membranes. What is the most common formation?
A. Beta Sheets
B. Alpha Helix
C. Lipid Chain
D. None of the above

Answer 7

B. Alpha helix

Question 8

What is the most common number of alpha helices in structural transmembrane proteins?
A. 4
B. 6
C. 7
D. 2

Answer 8

C. 7

Most common is 7 because is associated with G protein couple signaling

Question 9

Which of these is not a function of membrane proteins?
A. Cell adhesion
B. Receptor Signaling Systems
C. Transport
D. Enzymes
E. All of these are functions of membrane proteins

Answer 9

E. All of these are functions of membrane proteins

Question 10

What are the methods of characterization of lipid membranes?

Answer 10

1. ultracentrifugation
2. Density gradient ultracentrifugation
3. Electron microscopy
4. Fluorescence microscopy
5. Atomic force microscopy

Question 11

What do detergents do to membranes?

Answer 11

Detergents solubilize membranes

Question 12

What are the possible movements of lipids in the plasma membranes and how do they maintain membrane polarity?

Answer 12

1. Flippase - Outside to inside (PS, PE)
2. Floppase - inside to outside (PC,SL)
3. Scramblase - exchange mechanism (cholesterol)

Question 13

What is the lipid orientation in the ER membrane bilayers?

Answer 13

Scramblase

Question 14

What is the lipid orientation in the Plasma Membrane?

Answer 14

Flippase and Floppase

Question 15

What are lipid rafts?

Answer 15

Specialized domains predominantly within plasma membranes of cells which organize membrane proteins and glycolipids into groupings having functional implications in terms of receptor trafficking, neurotransmission, and membrane fluidity

Question 16

What is the difference between lipid rafts and plasma membranes?

Answer 16

Lipid rafts are enriched in cholesterol and sphingolipids

Lipid rafts tend to be resistant to dissociation by detergents which can freely dissociate the fluid membrane sections

Question 17

How do Caveolae form?

Answer 17

Form from lipid rafts

Question 18

What is membrane fusion?

Answer 18

Enveloped virus attaches to the cell membrane of recipient cell via receptors and receptors on the surface of the virus, followed by fusion where the envelope blends with the cell membrane and releases its genome into the cell

Question 19

Which of the following are examples of enveloped viruses containing human pathogens?
A. DNA viruses
B. RNA viruses
C. Retroviruses
D. All of the above

Answer 19

D. All of the above