Biology 263
Joel Piperberg
Page # 1
Cell Biology
November 24, 2009
Third Exam
Name _______________________________
I. Multiple Choice. Fill in the circle on the test form corresponding to the correct answer.
1. What might the cellular basis of a disease called familial hypercholesterolemia (an inherited disease
in which blood cholesterol levels are very high) be?
a. Cells produce too little cholesterol.
d. b and e
b. Receptors for LDL are mutated and do not bind it. e. LDL receptors bind too tightly to coated pits.
c. Receptors for HDL are not made.
2. Which of the following molecules would not pass directly through a lipid bilayer very easily?
a. water
b. a peptide hormone c. O2
d. sodium ions
e. b and d
3. Some membrane transport proteins allow molecules to leave or enter cells moving down their
concentration gradients without binding to the transport protein and without initiating a shape change
in that molecule. Such a molecule is called a(n) ________ protein.
a. integral
b. a, c and e c. transmembrane
d. a and c
e. carrier
4. Which of the following would not be likely to be triggered by second messengers?
a. programmed cell death c. disassembly of the extracellular matrix
e. initiation of cell division
b. new gene expression
d. changes in cell metabolic processes
5. You are studying a membrane transport molecule. You have discovered that it transports Cl- and
glucose. You have prepared inside-out and right-side out vesicles. If the above substances are found on
the opposite sides of either type of vesicle, transport is not seen to occur. If, on the other hand, glucose
and Cl- are placed outside the right-side out vesicles, transport takes place. Which of the following
statements about the transport molecule is true?
a. It is an antiport which would work if Cl- were placed inside and glucose were placed outside the
inside-out vesicles.
b. It is a symport which would work if Cl- and glucose were placed outside the inside-out vesicles.
c. It is a symport which would work if Cl- and glucose were placed inside the inside-out vesicles.
d. It is an antiport which would work if Cl- were placed outside and glucose were placed inside the
inside-out vesicles.
e. none of the above
6. A scientist crystallizes an enzyme isolated from an alien organism and analyzes its structure with Xray diffraction crystallography. He repeats the experiment after binding a substrate to the enzyme and
the results of crystallography suggest that the shape of the enzyme has not changed significantly.
What model of the enzyme active site would be supported by these findings?
a. The Fluid-Mosaic Model
c. The Induced Fit Model
e. The Mendel Model
b. The Lock-and-Key Model
d. The Chemiosmotic Model
7. The abbreviation that represents a change in the total thermal energy of the system is ______.
a. TS
b. S
c. G
d. H
e. H
8. According to the Second Law of Thermodynamics, ____________.
a. energy can be neither created nor destroyed
d. a system can never gain entropy.
b. heat is required for every process
e. none of the above
c. the entropy of the universe constantly increases
9. When the rate of product formation in an enzymatic reaction rises steadily, which of the following
things is (are) likely to be happening?
Biology 263
Joel Piperberg
Page # 2
a.
b.
c.
d.
e.
Cell Biology
November 24, 2009
Third Exam
Name _______________________________
A varying period of time is required for the conversion of substrate to product.
Each and every enzyme molecule is working at maximum speed.
Enzymes are being used only once.
all of the other answers
Substrate concentration is rising from an initially low value to higher values but has not yet saturated
the enzyme.
10. Two enzymes are analyzed to determine their abilities to bind to their substrates. Enzyme A has a
KM for its substrate of 4 mM and a Vmax of 48 µmoles of product produced per minute; enzyme B's KM
is 6.5 mM and a Vmax of 54 µmoles of product produced per minute. Which statement below is true?
a. Enzyme A exhibits lower affinity than B.
d. Enzyme B exhibits a lower affinity than A.
b. Enzyme B exhibits a higher G than A.
e. Enzyme A exhibits a higher affinity than B.
c. d and e
11. An enzyme that requires a solely organic component that assists its reaction might be said to require
a ___________.
a. cofactor b. coenzyme
c. conjugated protein
d. prosthetic group
e. a and b
12. Which of the following would be unlikely to be required by a metalloenzyme?
a. Zn+2 ions b. OH- ions
c. Mn+2 ions
d. Ca+2 ions
e. a, c and d
13. Protein hormones are big molecules that are incapable of passing through a membrane. How do
they “notify” the cell interior that they are present outside of the cell?
a. They cause receptors to activate G proteins.
d. a and e
b. They lead to cyclic nucleotide elongation.
e. They trigger the production of second messengers.
c. They directly activate phospholipase C.
14. Non-target cells for a ________ are cells that have _________ for that particular molecule.
a. hormone, no receptors
c. growth factor, receptors
e. a and c
b. hormone, acceptors
d. growth factor, no receptors
15. Peptide hormones can exert their effects by ___________.
a. causing the activation of inactive enzymes
d. a, b and c
b. indirectly activating G proteins
e. causing the deacetylation of enzymes
c. causing the activation of protein kinases
16. _______ is a small, hydrophobic molecule that dissolves in a membrane and increases ion
permeability sometimes with disastrous results for a cell.
a. Streptomycin
b. Gramicidin A
c. An ionophore
d. b and c
e. Myxomycin
17. Glucagon keeps the level of cAMP high by __________.
a. changing its receptor’s shape
d. increasing adenylate cyclase activity
b. activating the conversion of cAMP into ATP
e. causing the deactivation of a G protein
c. a and d
18. What kind of enzyme catalyzes the rearrangement of the atoms in the substrate?
a. lyase b. ligase
c. hydrolase
d. hydrolysase
e. isomerase
Biology 263
Joel Piperberg
Page # 3
Cell Biology
November 24, 2009
Third Exam
Name _______________________________
19. Which of the following represents kinetic energy?
a. water behind a dam
c. a boulder rolling down a hill
b. a tank filled with gasoline. d. c and e
20. A closed system ___________.
a. exchanges matter with its surroundings
b. can exchange energy with its surroundings
c. b and e
e. a thrown ball flying through the air
d. exchanges nothing with its surroundings
e. exchanges no matter with its surroundings
21. In the following branched metabolic pathway, a dotted arrow with a minus sign symbolizes inhibition
of a
metabolic step by an end product
L
M
Q
P
O
N
R
-
S
Which reaction(s) would not be inhibited if both Q and S are present in the cell in high concentrations?
a. none of the other answers b. O —> P
c. L —> N
d. O —> R
e. L —> M
22. With which of the following is clathrin associated?
a. coated vesicles
b. coated pits
c. fuzzy coat
d. a and b
23. Cells can respond to _________ by altering gene expression.
a. steroid hormones
b. CO
c. peptide hormones
d. a and c
e. a, b and c
e. glucose
24. Which of the following would be an example of the striking asymmetry found in cell membranes?
a. prevalence of carbohydrates on the outer surface of the cell
b. the distribution of carbohydrates on membrane cholesterol
c. the distribution of nucleic acids on membrane lipids
d. the distribution of branched phospholipid tails
e. a and b
25. What can trigger the secretion of neurotransmitters and/or the rearrangement of the cytoskeleton?
a. d and e
c. uptake of Ca2+ ions
e. binding of Ca2+ ions by calmodulin
+
2+
b. release of K ions
d. release of Ca ions
26. Which of the following produces inositol triphosphate directly through its activity?
a. protein kinase A b. adenylate cyclase c. phospholipase C d. protein kinase C
27. Which of the following could be an enzyme?
a. b, c and d
b. a polypeptide
c. a polynucleotide
d. RNase
28. At what point do living organisms attain equilibrium?
a. only at conception b. at death c. only during adolescence d. never
e. b and c
e. glycogen
e. until they die
Biology 263
Joel Piperberg
Page # 4
Cell Biology
November 24, 2009
Third Exam
Name _______________________________
29. According to the First Law of Thermodynamics, _____________.
a. the universe's entropy is decreasing d. energy cannot be destroyed
b. d and e
e. energy can be converted from one form to another
c. matter is cannot be destroyed
30. Which of the following is a property of enzymes?
a. They can be altered irreversibly during a reaction. d. c and e
b. They alter the equilibrium of a reaction.
e. They are usually present in low amounts.
c. They raise the energy of activation of a reaction.
31. A reaction that proceeds with a ____ of heat in the system is called an ______ reaction.
a. loss; exergonic
c. a and b
e. loss; exothermic
b. gain; endergonic
d. gain; endothermic
32. Enzymes effectively catalyze reactions by ___________.
a. lowering the G of a reaction and thus increasing the reaction rate
b. raising the G of a reaction and thus raising the reaction rate
c. raising the activation energy of a reaction and thus raising reaction rates
d. raising the activation energy and thus lowering the reaction rate
e. none of the above
33. What is one way by which living organisms might manage to get a reaction, A <—> B, which has a
small +G to run spontaneously?
a. by coupling with a smaller -H reaction
d. by adding some substrate A
b. by coupling to a larger -G reaction
e. b, c and d
c. by removing some product B
34. Which of the following is an example of the methods by which enzymes catalyze their reactions?
a. local alterations of potassium concentration
d. b and e
b. stressing a bond
e. transitory formation of covalent bonds
c. strengthening of bonds by electrophilic attack
35. The initially accepted model of the enzyme and its active site proposed by Emil Fischer in the late
1800s states that the enzyme __________.
a. has a flexible active site that fits the substrate more tightly after substrate has bound
b. interacts with substrate magnetically
c. works by locally unfolding and refolding around the substrate
d. possesses a rigid active site that can distinguish minor differences between potential substrates
e. is made of plastic
36. Which of the following is known to activate protein kinase C on at least some occasions?
a. Ca2+ ions b. IP3 c. diacylglycerol
d. K+ ions
e. a and c
37. Coated pits are a site at which _______ can occur.
a. receptor-mediated exocytosis
c. bulk-phase endocytosis
e. adsorptive exocytosis
b. adsorptive endocytosis
d. b and c
38. At what time is the clathrin coat removed from coated vesicles or coated pits?
a. before leaving the cell membrane
c. as the vesicle is forming
e. a and c
Biology 263
Joel Piperberg
Page # 5
b. once they are released to the cytoplasm
Cell Biology
November 24, 2009
Third Exam
Name _______________________________
d. as they burst
39. The fact that different types of cells contain different proteins explains why ____________.
a. different cell types respond in the same way to different hormones
d. a and b
b. different cell types respond differentially to the same hormone
e. b and c
c. the same cell types respond differentially to the same hormone
40. Ouabain is a very specific inhibitor of the active transport of potassium ions into the cell and is
therefore a valuable tool in studies of membrane transport mechanisms. Which of the following
processes in your own body would you expect to be sensitive to inhibition by ouabain?
a. passive transport of glucose into a muscle cell
b. active transport of sodium ions out of macrophages in adipose tissue
c. transport of phosphorus ions into liver cells
d. active uptake of lactose by the bacteria living in your intestine
e. none of the above
41. A molecule is known to bind to calcium ions released into the cytoplasm of a cell causing it to be
activated. It then is able to trigger a number of intracellular activities. Of what protein family is this
protein likely to be a member?
a. calpains
b. calmodulins
c. calculins
d. cadherins
e. calcmodulins
42. The Na+-K+ pump makes the cell exterior ___ because it pumps __ K+ ions into the cell for every __
Na+ ions pumped out of the cell.
a. neutral; 3; 3
b. negative; 2; 3
c. positive; 2; 3
d. negative; 3; 2
e. positive; 3; 2
43. A type of membrane transport that brings molecules into the cell and may be subject to competitive
inhibition would be ________.
a. receptor-mediated endocytosis
c. facilitated diffusion
e. bulk phase endocytosis
b. carrier-mediated transport
d. a, b and c
44. Some transport proteins convey molecules through a membrane up a concentration gradient by
binding to them and then transporting them through the membrane. These transport proteins have
maximal velocities of transport and can be affected by competitive and noncompetitive inhibitors.
What type of transport is coordinated by these proteins?
a. passive transport
c. active transport
e. c and d
b. facilitated diffusion
d. carrier-mediated transport
45. If you wish to limit the mobility of a protein in the membrane, which technique would you utilize if
you were a cell?
a. Make it very large.
d. Connect it to the nucleus.
b. Connect it to microtubules and/or intermediate filaments.
e. a, b and c
c. Attach it to many membrane lipids.
BONUS QUESTIONS
46. You homogenize the liver from a rat. After centrifugation to isolate the particulate fraction in the
pellet, you expose the resultant (initial) supernatant directly to glucagon and epinephrine. Which of
the following responses would occur following the abovementioned treatment?
a. Protein kinase activity drops.
d. Glycogen phosphorylase activity does not change.
b. Adenylate cyclase activity in the pellet drops. e. b and d
Biology 263
Joel Piperberg
Page # 6
Cell Biology
November 24, 2009
Third Exam
Name _______________________________
c. Phosphofructokinase activity decreases.
47. You treat the pellet from #46 with glucagon and epinephrine and then wash it with physiological
saline followed by centrifugation. The resultant wash supernatant is exposed to the supernatant
mentioned in #46? What happens to the activity of different enzymes in the supernatant?
a. Phosphorylase kinase activity drops.
d. b, c and e
b. Phosphoribosylkinase activity rises.
e. Glycogen synthase activity rises.
c. Protein kinase activity increases.
48. The initial supernatant from #46 is treated directly with cyclic UMP. What happens to enzyme
activities in the supernatant?
a. Phosphorylase kinase activity increases.
d. Glycogen synthase activity stays the same.
b. Glycogen phosphorylase activity does not change.
e. b and d
c. Protein kinase activity rises.
49. What happens to glycogen synthase activity in the initial supernatant from #46 after the addition of
membrane vesicles containing activated adenylate cyclase and ATP?
a. It increases. b. It decreases. c. It stays the same. d. It increases then decreases. e. It explodes.
50. Which of the following produces a second messenger?
a. phosphorylase kinase b. adenylate lipase C c. guanylate cyclase d. c and e
e. PLC
51. Which of the following directly or indirectly helps to open calcium channels in the smooth
endoplasmic reticulum?
a. an activated G protein
c. diacylglycerol
e. a and d
b. IP2
d. phospholipase C
LECTURE SHORT ANSWER QUESTIONS Please be as brief as possible.
1. What is the name of the process by which small, hydrophobic molecules pass through the cell
membrane? (1 point)
2. What is the name for a series of reactions in which each reaction is triggered by the one before it and
in which the result each reaction in the sequence is magnified? (1 point)
3. Why can water, a very hydrophilic molecule, pass freely through a lipid bilayer? (1 point)
4. Some channel proteins can allow things to pass through at all times. Others open in response to
specific stimuli at which time molecules or ions may pass through for a period of time after which the
channel closes. Name a stimulus that could open such a channel and what are such channels called?
(2 points)
5. a. Name one molecule that activates a G-protein-coupled receptor? (1 point)
Biology 263
Joel Piperberg
Page # 7
Cell Biology
November 24, 2009
Third Exam
Name _______________________________
b. Name 2 substrates of protein kinase A? (2 points)
c. What removes phosphate groups from proteins that have been directly or indirectly activated by
protein kinase after a hormone leaves its receptor and the hormone response needs to be ramped
down? (1 point)
d. What enzyme releases glucose from glycogen in response to epinephrine? (1 point)
SHORT ANSWER BONUS QUESTIONS
1. Sometimes two amino acid R groups containing carboxyl groups project into an enzyme's active site
but can differ in that one of them will be charged while the other is not. These two amino acid R
groups may even be very close together, being separated by no more than 3 Å. Explain how two
amino acid R groups so close together in the protein could differ so greatly in their charge. (1 point)
2. The reaction G + S <—> K + L is highly exothermic and results in an increase in entropy? Is the G
of this reaction positive, negative or 0? How do you know? (2 points)
3. How does protein kinase "know" which proteins it should phosphorylate? (1 point)
4. Who is Professor Moriarty? (1 point)
5. a. Name a molecule that activates a protein kinase A? (1 point)
b. What enzyme polymerizes glucose into glycogen? (1 point)
6. What is the three-legged trimer that serves as the structural subunit of the clathrin coat? (1 point)
Biology 263
Joel Piperberg
Page # 8
Cell Biology
November 24, 2009
Third Exam
Name _______________________________
7. What two features must coupled reactions have? (2 points)
8. What is the thermodynamic term that deals with randomness in the universe? (1 point)
9. What is another name for an organic cofactor? (1 point)
10. To what part of an enzyme does a competitive inhibitor bind? (1 point)
11. ________________ is energy of motion. (1 point)
12. What is the advantage of positive cooperativity? (1 point)
13. Since _______ organisms are ______ systems, they exhibit equilibrium instead of ________.
(3 points)
14. What two second messengers are produced from phosphatidylinositol diphosphate? (2 points)
15. What is the only gemstone composed of just one chemical element? What is the element? (2 points)