3.1 study guide

Question 1

You screen for genetic mutants that are compromised in signaling downstream of your receptor. One
of the mutants you discover has a deletion in a gene encoding an unknown protein with a very similar
amino acid sequence to a known membrane-spanning beta barrel. How many amino acids are required
for one of the strands in the beta barrel to span the entire membrane?
a. 20
b. 15-17
c. 12-14
d. 7-9
e. 4-6

Answer 1

7-9

Question 2

How can you determine which parts of the protein form beta strands that span the membrane?
a. By analyzing the protein using a hydropathy plot
b. Through comparison of sequence alignments with beta strands of the known beta barrel protein
c. Both of these techniques would work equally well
d. Neither of these techniques would yield any information

Answer 2

Through comparison of sequence alignments with beta strands of the known beta barrel protein

Question 3

When the membrane-spanning beta barrel was isolated and crystallized, it was found to have an
annulus. What is true about the annulus?
a. It is made up of lipids
b. It can form a grease seal around membrane proteins
c. The annulus can remain associated with the protein during isolation from the membrane
d. It helps hold the protein in the proper orientation within the membrane
e. All of the above

Answer 3

All of the above

Question 4

You analyze a membrane sample in the lab and find it to be enriched in cholesterol and high in protein
content. Which of the following is probably true about this sample?
a. It had a higher than normal density of lipid rafts/microdomains
b. It was more difficult to degrade than average membrane samples
c. There is also a higher than average sphingolipid content
d. A western blot of the extracted proteins using anti-caveolin antibody would likely yield a strong band
e. All of the above

Answer 4

All of the above

Question 5

Some proteins are held in the membrane by a farnesyl tail (prenylation). Where on the protein is the
farnesyl tail attached?
a. To a Cys anywhere in the protein
b. To a carboxyl terminus Cys
c. To an amino terminus Gly
d. To a Ser anywhere in the protein
e. To a Gly anywhere in the protein

Answer 5

To a carboxyl terminus Cys

Question 6

What is the function of the caveolin scaffolding domain?
a. To promote dimerization
b. To transverse the membrane
c. To link the oligimerization and transmembrane domains
d. To attach to the membrane using a palmitoyl tail
e. All of the above

Answer 6

To link the oligimerization and transmembrane domains

Question 7

Which of these membrane fusion proteins are located in the plasma membrane
a. SNAP25
b. vSNARE
c. tSNARE
d. Both a and b
e. Both a and c

Answer 7

SNAP25 and tSNARE

Question 8

What is the function of the NPA motif in aquaporin?
a. It contains a histidine residue that narrows the interior channel to 2.8 Angstroms
b. It contains asparagine residue that hydrogen bond with water molecules
c. It breaks up hydrogen bonded chains of water molecules
d. Both a and b
e. Both b and c

Answer 8

-It contains asparagine residue that hydrogen bond with water molecules
-It breaks up hydrogen bonded chains of water molecules

Question 9

In the selectivity cone of the potassium transporter, which is a function of the carbonyl cage?
a. To strip water from the potassium ions
b. To rehydrate potassium ions
c. To act as a voltage gate
d. To migrate across the plasma membrane
e. All of the above

Answer 9

To strip water from the potassium ions

Question 10

For voltage-gated potassium channels, membrane depolarization causes:
a. The membrane surface inside the cell to become less negative
b. The voltage sensor helix to move towards the outside of the membrane
c. Channel opening
d. All of the above
e. Both b and c

Answer 10

All of the above

Question 11

Which of these is true of ion channels?
a. They are saturable
b. They can transport ions in both directions
c. They can transport ions against their gradient
d. All of the above
e. None of the above

Answer 11

They can transport ions in both directions