Questions in this chapter you should be able to answer:

1
Membrane Structure Chapter 11
Questions in this chapter you should be able to
answer Chapter 11- s1, 2, 3, 4, 5, 8, 9, 10,
11, 15, 19
2
Membranes are described as a 2-dimensional
liquid. Why?
Jmol Membrane model
Laser tweezers.mov
Membrane fluidity.mov
3
How can we measure membrane fluidity? FRAP
Fluorescence Recovery After Photobleaching GFP
Green fluorescent protein Cell fusion
also shows fluidity See Figure 11-34
P 384
FRAP.mov
4
What factors determine how fluid a membrane
is? Properties of P-lipids Chain
length Saturation Properties of
membranes Cholesterol content Cytoskeleton
association
5
What are the principal membrane
lipids? Phospholipids Glycolipids Other
membrane lipids (not phospholipids) Cholesterol
Cerebrosides Sphingolipids Ceramide
6
What does it mean to say that lipid bilayers are
asymmetrical?
P-lipids are synthesized on the ER
membrane. How do they get to other side of
membrane?
7
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
???
8
How are membrane proteins embedded in the bilayer?
Why is an alpha helix a common structure?
Jmol Transmembrane proteins
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?
10
How is the cell membrane structurally
reinforced? -- Cell cytoskeleton -- also
influences fluidity
11
Why are carbohydrates particularly abundant on
the cell surface?
Functions Surface protectant Cell
recognition Cell adhesion -- extracellular
matrix
12
How can protein movement in cell membrane be
restricted?
Consider challenge of intestinal epithelium
Fig 21-22 p 712
13
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 will unfold proteins
and disrupt their ability to interact with other
proteins) and centrifuge the mixture. The
membranes and their constituent proteins form a
pellet while the proteins liberated from the
membranes by the urea wash remain in the
supernatant. When you check each of the factions
for the presence of A or B, you obtain the
results given below.
Which of the following statements are consistent
with your results? (a) Proteins A and B are both
integral membrane proteins. (b) Protein A is an
integral membrane protein that interacts with B,
a peripheral membrane protein. (c) Protein B is
cytosolic protein that interacts only with the
mutant form of A. (d) The mutation in A affects
its ability to interact with B. (e) The mutation
in B prevents its integration into the membrane.