1. On average, how many amino acids engaged in predominantly hydrophobic helices does it take to cross the hydrophobic part of the membrane?
A) about 10 amino acids
B) about 20 amino acids
C) at least 40 amino acids
D) about 2 - 3 amino acids
E) None of these are correct.

2. What kind of enzyme removes a phosphate groups from a substrate for the purpose of activating or deactivating them?
A) phosphatases
B) protein kinases
C) flippases
D) glycosyltransferases
E) carboxypeptidase

3. Which of the following is not a function of peripheral proteins?
A) mechanical support for membrane
B) enzymes
C) receptors
D) anchor for integral proteins
E) factors that transmit transmembrane signals

4. What GTP-binding protein plays a regulatory role by initiating vesicle formation and by regulating the assembly of the vesicle's COPII coat?
A) Sar1
B) Gar1
C) ARF1 (adenosylation ribose factor)
D) Ras
E) Src
5. What technique below is often used to identify transmembrane segments of integral proteins?
A) Lineweaver-Burk plot
B) Michaelis-Menten plot
C) hydrophilicity plot
D) hydropathy plot
E) titration plot

6. What causes the membrane potential to return to the normal negative value after an action
potential has occurred?
A) opening of a voltage-gated K+ channel
B) opening of a voltage-gated Na+ channel
C) closing of a voltage-gated K+ channel
D) opening of a ligand-gated Na+ channel
E) opening of a voltage-gated K+ facilitated transporter

12. Phosphatidylethanolamine (PE) is concentrated in the inner leaflet of the plasma membrane and tends to promote the curvature of the membrane, which is important in _________.
A) membrane vesicle
B) membrane fragmentation
C) Mitosis
D) signal transduction
E) insertation of transmembrane domains

12. What is the distinguishing characteristic of a P-type pump?
A) It must be pumped during the cycle.
B) It must be phosphorylated during the cycle.
C) It must be protonated during the cycle.
D) It must be deprotonated during the cycle.
E) It must be potassiumated during the cycle.

15. With what structure is the RER often seen to be continuous, as seen by its association with ribosomes?
A) the inner membrane of the nuclear envelope
B) the outer membrane of the nuclear envelope
C) the outer mitochondrial membrane
D) the outer chloroplast membrane
E) the Golgi complex

16. What are the two sites within a cell at which protein synthesis is generally thought to occur?
A) cytosolic surface of RER and cisternal surface of RER
B) cisternal surface of RER and free ribosomes
C) cytosolic surface of RER and free ribosomes
D) cytosolic surface of RER and cytosolic surface of SER
E) free ribosomes and cytosolic surface of SER
Section III _Extended Multiple Choice; clearly circle the letter corresponding to the best
answer and explain your rationale:
Answer four of the following questions.

1. Where in a myelinated axon are nearly all of the ion channels concentrated?
A) the cell body
B) nodes of Ranvier
C) dendrites
D) axon terminals
E) neuron nucleus
Explain:

2. Why are the proteins being separated on an SDS polyacrylamide gel attracted equally to the positive electrode?
A) They carry a relatively uniform positive charge distribution
B) They carry a relatively uniform negative charge distribution.
C) They are all the same molecular weight.
D) They are all the same size.
E) They all have the same degree of hydrophobicity.
Explain:

3. Which amino acid replacement for isoleucine would be least likely to alter a transmembrane domain?
A) Serine
B) Tyrosine
C) Cysteine
D) Lysine
E) Leucine
Explain:

4. Why are integral membrane proteins difficult to study?
A) They are difficult to isolate in soluble form due to their hydrophobic transmembrane domains.
B) They are difficult to isolate in soluble form due to their hydrophilic transmembrane domains.
C) They are so small.
D) They are so large.
E) None of these are correct.
Explain:

5. What is the effect on a yeast cell of the presence of a mutant gene involved in vesicle fusion?
A) The ER shrank.
B) The Golgi complex expanded greatly.
C) Cells accumulated expanded ER cisternae.
D) Cells amassed an excess number of unfused vesicles.
E) The nucleus became swollen.