BIOL 102 PRACTICE MIDTERM EXAM
Instructions: This exam is worth- -points, plus 1 point altogether for writing your name and section
letter at
the top of each front page, for a total of points. This exam is closed-note, not collaborative, and
phones
should be put away. You are allowed a maximum of 75 minutes from the start of our class period
in YSB Marsh. [If you are approved for extra time accommodations, you should be in a separate
room reserved for your full-time accommodation, not in YSB Marsh.] If you would like the
opportunity for re-grade, you must write in pen, not pencil. Write LEGIBLY; if the grader cannot
read the answer, it will be awarded zero point. GOOD LUCK!
Question 1. (4 pts) Multiple Choice. Circle the only one answer.
1. Pumps are transporters that are able to harness energy provided by other components
in the cells to drive the movement of solutes across membranes, against their
concentration gradient. This type of transport is called:
a. active transport.
b. free diffusion.
c. facilitated diffusion.
d. passive transport.
2. Which of the following organelles is not part of the endomembrane system?
a. Golgi apparatus
b. the endosome
c. mitochondria
d. lysosomes
3. Proteins that are fully translated in the cytosol and lack a sorting signal will end up in the
a. cytosol.
b. mitochondria.
c. interior of the nucleus.
d. nuclear membrane.
4. Most proteins destined to enter the endoplasmic reticulum
a. are transported across the membrane after their synthesis is complete.
b. are completely translated on free ribosomes in the cytosol.
c. begin to cross the membrane while still being synthesized.
d. remain within the endoplasmic reticulum.
, Question 2. (8 pts) For the following statements, decide whether they are True or False. If false,
briefly justify in a sentence.
1. A protein that relies on protein–protein interactions to stabilize its membrane association
is classified as a peripheral membrane protein because it can be dissociated without the
use of detergents.
True
2. Membrane proteins that pump ions in and out of the cell are classified as enzymes.
False. Membrane proteins that pump ions in either direction across the membrane are in the functional
class of transporters – either channels or pumps.
3. When a mouse cell is fused with a human cell, the movement of the respective
membrane proteins is restricted to their original locations at the time of fusion.
False. After about 1 hour, the mouse and human proteins present on the surface of the fused cell
are found evenly dispersed throughout the plasma membrane.
4. In order to study the activity of isolated transmembrane proteins, the membrane
lipids must be completely stripped away.
False. The region of the protein that normally crosses the membrane must be stabilized by the
presence of phospholipids for the purified protein to be active. For this reason, purified membrane
proteins are often reconstituted into artificial lipid bilayers.
5. The rate at which a solute that is transported across the membrane via a
channel is linearly proportional to that of the solute concentration differential
on either side of the membrane.
True
6. The differences in permeability between artificial lipid bilayers (liposomes) and cell
membranes arise from variations in phospholipid content.
False. The primary difference between cell membranes and artificial membranes is that cell
membranes have proteins responsible for creating a selective permeability, which varies with the
location and function of the membrane.
7. Facilitated diffusion can be described as the favorable movement of one solute down its
concentration gradient being coupled with the unfavorable movement of a second solute
up its concentration gradient.
False. This describes coupled indirect active transport, which is one type of active transport.
Facilitated diffusion can also be called passive transport, in which a solute always moves down
its concentration gradient.
8. Signal sequences that direct proteins to the correct compartment are encoded in
the amino acid sequence and sufficient for targeting a protein to its correct
destination.
True
Question 3. (2 pts) Explain the reasons why membrane proteins are more difficult to isolate and
Instructions: This exam is worth- -points, plus 1 point altogether for writing your name and section
letter at
the top of each front page, for a total of points. This exam is closed-note, not collaborative, and
phones
should be put away. You are allowed a maximum of 75 minutes from the start of our class period
in YSB Marsh. [If you are approved for extra time accommodations, you should be in a separate
room reserved for your full-time accommodation, not in YSB Marsh.] If you would like the
opportunity for re-grade, you must write in pen, not pencil. Write LEGIBLY; if the grader cannot
read the answer, it will be awarded zero point. GOOD LUCK!
Question 1. (4 pts) Multiple Choice. Circle the only one answer.
1. Pumps are transporters that are able to harness energy provided by other components
in the cells to drive the movement of solutes across membranes, against their
concentration gradient. This type of transport is called:
a. active transport.
b. free diffusion.
c. facilitated diffusion.
d. passive transport.
2. Which of the following organelles is not part of the endomembrane system?
a. Golgi apparatus
b. the endosome
c. mitochondria
d. lysosomes
3. Proteins that are fully translated in the cytosol and lack a sorting signal will end up in the
a. cytosol.
b. mitochondria.
c. interior of the nucleus.
d. nuclear membrane.
4. Most proteins destined to enter the endoplasmic reticulum
a. are transported across the membrane after their synthesis is complete.
b. are completely translated on free ribosomes in the cytosol.
c. begin to cross the membrane while still being synthesized.
d. remain within the endoplasmic reticulum.
, Question 2. (8 pts) For the following statements, decide whether they are True or False. If false,
briefly justify in a sentence.
1. A protein that relies on protein–protein interactions to stabilize its membrane association
is classified as a peripheral membrane protein because it can be dissociated without the
use of detergents.
True
2. Membrane proteins that pump ions in and out of the cell are classified as enzymes.
False. Membrane proteins that pump ions in either direction across the membrane are in the functional
class of transporters – either channels or pumps.
3. When a mouse cell is fused with a human cell, the movement of the respective
membrane proteins is restricted to their original locations at the time of fusion.
False. After about 1 hour, the mouse and human proteins present on the surface of the fused cell
are found evenly dispersed throughout the plasma membrane.
4. In order to study the activity of isolated transmembrane proteins, the membrane
lipids must be completely stripped away.
False. The region of the protein that normally crosses the membrane must be stabilized by the
presence of phospholipids for the purified protein to be active. For this reason, purified membrane
proteins are often reconstituted into artificial lipid bilayers.
5. The rate at which a solute that is transported across the membrane via a
channel is linearly proportional to that of the solute concentration differential
on either side of the membrane.
True
6. The differences in permeability between artificial lipid bilayers (liposomes) and cell
membranes arise from variations in phospholipid content.
False. The primary difference between cell membranes and artificial membranes is that cell
membranes have proteins responsible for creating a selective permeability, which varies with the
location and function of the membrane.
7. Facilitated diffusion can be described as the favorable movement of one solute down its
concentration gradient being coupled with the unfavorable movement of a second solute
up its concentration gradient.
False. This describes coupled indirect active transport, which is one type of active transport.
Facilitated diffusion can also be called passive transport, in which a solute always moves down
its concentration gradient.
8. Signal sequences that direct proteins to the correct compartment are encoded in
the amino acid sequence and sufficient for targeting a protein to its correct
destination.
True
Question 3. (2 pts) Explain the reasons why membrane proteins are more difficult to isolate and
