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Membrane Structure Chapter 11. Questions in this chapter you should be able to answer: Chapter 11- #s1 - 20. Membranes are described as a “2-dimensional liquid”. Why?. Jmol Membrane model. Laser tweezers. Membrane fluidity. How can we measure membrane fluidity?

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Membrane Structure

Chapter 11

Questions in this chapter you should be able to answer:

Chapter 11- #s1 - 20

Membrane Structure


Membranes are described as

a “2-dimensional liquid”. Why?

Jmol Membrane model

Laser tweezers

Membrane fluidity

Membrane Structure


How can we measure membrane fluidity?

FRAP: ‘Fluorescence Recovery After Photobleaching’

GFP: Green fluorescent protein

Cell fusion also

shows fluidity

See Figure 11-32

P 384

Membrane Structure


What factors determine how fluid a membrane is?

Properties of P-lipids: Chain length Saturation

Properties of membranes: Cholesterol content Cytoskeleton association

Membrane Structure


What are the principal membrane lipids?



Other membrane lipids

(not phospholipids)





Membrane Structure


How are P-lipids distributed in lipid bilayers?

Scamblase vs Flippase

P-lipids are synthesized on the ER membrane….

How do they get to other side of membrane?

How is asymmetry achieved?

From MBOC ed 5

Membrane Structure


What are the principal functions of membrane proteins?

How are membrane proteins connected to the membrane?

Transmembrane (intergral)

Single-pass Multi-pass

Membrane associated (peripheral)

Covalent vs Noncovalent

Membrane Structure


Why do transmembrane proteins occur as alpha helices and beta-pleated sheets??

Jmol Transmembrane proteins

Membrane Structure


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


What do we know about

the structure of bacteriorhodopsin?





Membrane Structure


How is the cell membrane structurally reinforced?

-- Cell cytoskeleton

-- also influences fluidity

Membrane Structure


Why are carbohydrates particularly abundant on the cell surface?


Surface protectant

Cell recognition

Cell adhesion

-- extracellular matrix

Membrane Structure


How can protein movement in cell membrane be restricted?

Consider challenge of intestinal epithelium…

Fig 12-18 p 399

Membrane Structure


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 each type of mutant cell 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.

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-A alter its properties.

(d) Which result(s) most indicate an interaction between A and B. Explain.

Membrane Structure