1. Membrane Structure Chapter 11
Questions in this chapter you should be able to answer:
Chapter 11- #s1 - 19
Membrane Structure

2. Membranes are described as a “2-dimensional liquid”. Why?
Jmol membrane model
Laser Tweezers
Membrane Fluidity
Membrane Structure

3. How can we measure membrane fluidity?
FRAP: ‘Fluorescence Recovery After Photobleaching’
GFP: Green fluorescent protein
Cell fusion also
shows fluidity
See Figure 11-30
P 378
FRAP
Membrane Structure

4. What factors determine how fluid a membrane is?
Properties of P-lipids: Chain length Saturation
Properties of membranes: Cholesterol content Cytoskeleton association
Membrane Structure

5. What are the principal membrane lipids?
Phospholipids
Glycolipids
Other membrane lipids
(not phospholipids)
Cholesterol
Cerebrosides
Sphingolipids
Ceramide
Membrane Structure

6. How are P-lipids distributed in lipid bilayers?
Scramblase vs Flippase
P-lipids are synthesized on the ER membrane….
How do they get to other side of membrane?
How is asymmetry achieved?
Membrane Structure

7. What are the principal functions of membrane proteins?
How are membrane proteins connected to the membrane?
Membrane associated (peripheral)
Covalent vs Noncovalent
Transmembrane (integral)
Single-pass Multi-pass
Membrane Structure

8. Why do transmembrane proteins occur as alpha helices and beta-pleated sheets??
Jmol Transmembrane proteins
Membrane Structure

9. How can membrane proteins be purified and studied?
-- detergents ‘mimic’ P-lipid structure around proteins
Question 11-5
Why is red part hydrophilic and blue part hydrophobic?
Membrane Structure

10. the structure of bacteriorhodopsin?
What do we know about
the structure of bacteriorhodopsin?
Function?
Structure?
Mechanism?
Bacteriorhodopsin
Membrane Structure

11. How is the cell membrane structurally reinforced? -- Cell cytoskeleton
-- also influences fluidity
Membrane Structure

12. Why are carbohydrates particularly abundant on the cell surface?
Functions:
Surface protectant
Cell recognition
Cell adhesion
-- extracellular matrix
Membrane Structure

13. How can protein movement in cell membrane be restricted?
Consider challenge of intestinal epithelium…
Fig p 395
Membrane Structure

14. After urea wash and centrifugation
You have isolated two mutants of a normally pear-shaped microorganism that have lost their distinctive shape and are now round. One of the mutants has a defect in a protein you call A and the other has a defect in a protein you call B. You grind up mutant and normal cells separately and separate the plasma membranes from the cytoplasm by centrifugation. You then wash the membrane fraction with a low concentration of urea ( which disrupts their ability to interact with other proteins) and centrifuge the mixture. The membranes and their constituent proteins form a pellet while the proteins liberated by the urea wash remain in the supernatant. When you check each of the fractions for the presence of A or B, you obtain the results given below.
First cell extract
After urea wash and centrifugation
Membrane
Cytosol
Supernatant
Normal cells
A and B
no A or B B A
Mutant A
Mutant B
Answer the following statements about your results?
(a) Which is an integral and which is a peripheral membrane-associated protein. The results for which cell-type shows this?
(b) How does the mutation to protein-A alter its properties?
(c) How does the mutation to protein-B alter its properties?
(d) Which result(s) most indicate an interaction between A and B? Explain.
Membrane Structure