Biology 362
Cell Biology
Joel Piperberg
April 17 - 19, 2018
Second Exam
Page # 1
Name ___________________________________
I. Multiple Choice. Fill in the circle on the test form corresponding to the correct answer.
1. In the following branched metabolic pathway, a dotted arrow with a minus sign symbolizes
inhibition of a metabolic step by an end product.
Which reaction(s) would be inhibited if both Q and S are present in the cell in high concentrations?
a. b, d and e b. O —> P
c. b and d
d. O —> R
e. L —> M
2. Two enzymes are analyzed to determine their abilities to bind to their substrates. Enzyme A
has a KM for its substrate of 9.3 mM and a Vmax of 65 µmoles of product produced per minute;
enzyme B has a KM is 5.5 mM and a Vmax of 32 µmoles of product produced per minute. Which
statement below is true about the relationship between the enzyme and its substrate?
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
3. Which of the following is typical of positive cooperativity?
a. The enzyme has only one subunit.
b. The enzyme has more than one subunit.
c. Substrate bound at one active site increases the binding activity of other active sites.
d. Substrate bound at one active site decreases the binding activity of other active sites.
e. b and c
4. The product of a metabolic pathway binds to the first enzyme in that pathway, inhibiting that
enzyme and slowing down the pathway as a result. What type of inhibition does this describe?
a. competitive inhibition b. end-product inhibition c. allosteric inhibition d. a, b and c e. b and c
5. An enzyme that requires a permanently associated metal ion and 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 d
6. Which of the following directly or indirectly helps to open calcium channels in the smooth
endoplasmic reticulum?
a. an inactivated G protein
b. IP3 c. DAG d. protein kinase C
e. b and d
7. Fibronectin is likely to have binding sites for which of the following molecules?
a. cell surface proteins
b. collagen
c. tubulin
d. GAGs
e. a, b and d
8. What kind of enzyme typically catalyses the formation of covalent bonds using the energy
released by the cleavage of ATP?
a. lyase b. ligase
c. hydrolase
d. oxidoreductase
e. isomerase
Biology 362
Cell Biology
Joel Piperberg
April 17 - 19, 2018
Second Exam
Page # 2
Name ___________________________________
9. What is the name of the short sequence of amino acids in proteins to which protein kinases add
phosphate groups?
a. an aminoids b. a motif
c. a phosphoid
d. a credenza e. a mastiff
10. Integrins bind to a specific three amino acid sequence (designated RGD) in a number of
proteins. A dish is coated with a protein containing the RGD sequence. Some cultured cells with
integrins embedded in their membranes were added to the culture dish along with tripeptides with
the RGD sequence. The cells do not bind to the dish. This is an example of _________.
a. allosteric inhibition
c. a and b
e. receptor degradation
b. noncompetitive inhibition d. competitive inhibition
11. When the rate of product formation in an enzymatic reaction rises steadily, which of the
following things is (are) likely to be happening?
a. A varying period of time is required for the conversion of substrate to product.
b. Each and every enzyme molecule is working at maximum speed.
c. Enzymes are being used more than once.
d. c and e
e. Enzyme concentration is rising from an initially low value to higher values in the presence of
unlimited amounts of substrate.
12. What property of the components of the chick embryo cornea gives it its strength?
a. the small size of the collagen molecules
d. the parallel arrangement of cellulose
b. the orthogonal arrangement of collagen molecules e. b and d
c. the parallel arrangement of collagen molecules
13. Which of the following cannot be an enzyme?
a. b, c and d
b. a protein
c. RNA
d. amylase
e. amylose
14. Peptide hormones can exert their effects by ___________.
a. inactivating active enzymes
c. activating receptor tyrosine kinases
b. indirectly activating adenylate cyclase d. causing the acetylation of enzymes
e. a, b and c
15. Epinephrine keeps the level of cAMP high by _____________.
a. changing its receptor’s conformation
d. inhibiting the activity of adenylate cyclase
b. activating the conversion of ATP into cAMP
e. causing the activation of a G protein
c. a, b and e
16. Target cells for a ________ are cells that have _________ for that particular molecule.
a. hormone, receptors
c. growth factor, receptors
e. a and c
b. hormone, acceptors
d. growth factor, no receptors
17. 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 indirectly activate adenylate cyclase.
b. They lead to cyclic nucleotide degradation.
c. They directly activate protein kinases.
d. a and e
e. They can trigger the cytoskeleton’s ability to make cAMP.
Biology 362
Cell Biology
Joel Piperberg
April 17 - 19, 2018
Second Exam
Page # 3
Name ___________________________________
18. Which of the following would not be likely to be triggered by second messengers?
a. death of abnormal cells
c. polymerization of Ca2+ ions e. mitotic initiation
b. turning off gene expression d. cell metabolism regulation
19. Which of the following can be involved in turning off a hormone response?
a. protein kinase b. phosphatase c. phosphodiesterase d. b and c e. high hormone secretion
20. Which of the following is known to activate protein kinase C under at least some circumstances?
a. phorbol esters b. Ca2+ ions c. DAG d. a, b and c e. b and c
21. Which of the following is directly activated by cAMP?
a. phosphodiesterase b. phosphatase c. protein kinase A
d. RTKs
e. phosphorylase kinase
22. Which of the following is likely to be a difference between a natural inhibitor and a poison?
a. A natural inhibitor is always smaller than a poison.
b. A natural inhibitor is always larger than a poison.
c. A natural inhibitor binds its enzyme more tightly than a poison.
d. A natural inhibitor binds its enzyme less tightly than a poison.
e. a and d
23. Which of the following could be true if an active enzyme is inhibited at its regulatory site
with a molecule called P2?
a. P2 would not resemble the normal substrate for the enzyme.
b. The quantity of raw substrate would have to be very high.
c. P2 is an alternate substrate for the enzyme.
d. a and c
e. More water would have to be made available.
24. An enzyme is inhibited at its substrate-binding site by an inhibitor (P3). Which of the
following would have to be true about P3?
a. P3 would have to be similar to the enzyme.
d. P3 attracts the substrate to the active site.
b. P3 would be similar in structure to the substrate.
e. b and c
c. P3 is likely to differ slightly from the substrate in structure.
25. You expose a pure unknown culture of bacteria to a stain containing crystal violet and iodine.
After a rinse, the stain is not retained by the bacteria. Which of the following could be a
possible interpretation of this result?
a. It is a Gram-positive bacterium.
c. It might be E. coli.
e. b and c
b. It is a Gram-negative bacterium.
d. It might be Streptococcus.
26. Which of the following is typical of negative cooperativity?
a. The enzyme has only one subunit.
b. The enzyme has more than one active site.
c. Substrate bound at one active site increases the binding activity of other active sites.
d. Substrate bound at one active site decreases the binding activity of other active sites.
e. b and d
27. Which second messenger is produced by phospholipase C?
a. DAG
b. protein kinase C
c. a and d
d. IP3
e. diacyglyceric acid
Biology 362
Cell Biology
Joel Piperberg
April 17 - 19, 2018
Second Exam
Page # 4
Name ___________________________________
28. What extracellular matrix protein is known for having high tensile strength and forming an
insoluble framework that helps to determine the mechanical properties of the matrix?
a. fibronectin b. laminin c. collagen
d. proteoglycan e. protein kinase
29. Which of the following is a property of enzymes?
a. They are altered reversibly during a reaction.
d. a and c
b. They alter the equilibrium of a reaction.
e. They are usually present in high amounts.
c. They lower the energy of activation of a reaction.
30. You have just found a dead deep-sea creature in your fishing nets. It appears to be a new
species. During the post-mortem attempt to classify the organism, a jelly-like, extracellular
mass is found in the abdomen. It is found to contain protein and carbohydrate and lots of
water. What kind of molecule would you expect to find in the jelly-like mass?
a. glycoprotein aggregates b. GAGs c. mucoproteins d. mucopolynucleotides e. b and c
31. 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. lowering 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
32. Which of the following is a way by which living organisms might manage to get a reaction, A <—> B,
which has a large +G to run spontaneously?
a. by coupling with a larger -H reaction
d. by removing some substrate A
b. by coupling to a larger -G reaction
e. b, c and d
c. by adding some product B
33. Which of the following is an example of the methods by which enzymes catalyze their reactions?
a. local alterations of glycerol concentration
d. b, c and e
b. stressing a bond
e. transient formation of ionic or covalent bonds
c. weakening of bonds by electrophilic attack
34. The presently accepted model of enzyme action proposed by Daniel Koshland in the 1960s
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
35. Which word or words below is not associated with an RTK?
a. insulin
b. tyrosine
c. cAMP
d. transautophosphorylation
e. a and d
36. What can trigger the secretion of histamine and/or the contraction of muscle cells?
a. d and e
c. uptake of Ca2+ ions
e. release of Ca2+ ions from calmodulin
+
2+
b. release of Na ions
d. release of Ca ions
Biology 362
Cell Biology
Joel Piperberg
April 17 - 19, 2018
Second Exam
Page # 5
Name ___________________________________
37. Which of the following can be activated indirectly by the binding of inositol triphosphate to an
SER channel protein?
a. protein kinase A b. adenylate cyclase c. phospholipase C d. protein kinase C e. b and c
38. Cells can respond to steroid hormones by ___________.
a. altering nucleic acids
c. altering the activity of metabolic enzymes
b. altering gene expression
d. destroying peptide hormones
e. b and c
39. 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 muscle contraction. Which of the following would be
a correct name for this molecule?
a. troponin
b. a calmodulin
c. a and b
d. a cadherin
e. a calcmodulin
40. What explains how different cell types respond differentially to the same hormone?
a. The cells have different receptors for the hormone that initiate different processes.
b. Different cell types contain different sets of proteins that are activated by the hormone.
c. Different cell types have different G proteins
d. b and c
e. a and b
41. What second messenger appears to be responsible for relieving the pain of angina?
a. CO b. nitric oxide c. monoamine oxidase d. NO
e. b and d
42. The glycocalyx is composed of ________________.
a. carbohydrates attached by noncovalent bonds to membrane glycoproteins
b. carbohydrates attached by weak interactions to membrane glycolipids
c. the cell coat and the fuzzy layer
d. a and b
e. a, b and c
43. The function of the glycocalyx is ________________.
a. to act as a lubricant
d. b and c
b. to control interactions between cells and their substrates
e. to expedite cell division
c. to prevent unwanted molecules from getting to the cell membrane
44. Which of the following would be likely to be required by a metalloenzyme?
a. Fe+2 ions b. hydroxyl ions
c. Mg+2 ions
d. Ca+2 ions
e. a, c and d
45. Which of the following would not explain a rise in the rate of product production?
a. products changing the pH of the medium
b. d and e
c. renaturing the enzyme
d. a rise in substrate concentration from an initially very low concentration
e. a rise in enzyme concentration in the presence of unlimited amounts of substrate
II. Multiple Choice Bonus
46. You homogenize the liver from a rat. After centrifugation to isolate the particulate fraction in
the pellet, you directly expose the resultant (initial) supernatant to glucagon and epinephrine.
Which of the following responses would occur following the abovementioned treatment?
a. Protein kinase activity does not change.
d. Glycogen synthase activity rises.
b. Adenylate cyclase activity in the pellet rises.
e. a and b
c. Phosphofructokinase activity increases.
Biology 362
Cell Biology
Joel Piperberg
April 17 - 19, 2018
Second Exam
Page # 6
Name ___________________________________
47. The initial supernatant from #46 is treated directly with cyclic AMP. What happens to
enzyme activities in the supernatant?
a. Phosphorylase kinase activity decreases.
d. Glycogen synthase activity decreases.
b. Glycogen phosphorylase activity rises.
e. b and d
c. Protein kinase activity remains the same.
48. What happens to phosphorylase kinase activity in the initial supernatant from #46 after the
addition of 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.
49. 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 initial supernatant
mentioned in #46. What happens to the activity of different enzymes in this initial supernatant?
a. Glycogen phosphorylase activity rises.
d. a and e
b. Phosphoribosylkinase activity drops.
e. Glycogen synthase activity drops.
c. Protein kinase activity decreases.
50. Which of the following directly produces a second messenger?
a. phosphorylase kinase b. adenylate lipase C c. adenylate cyclase d. c and e e. phospholipase C
III. Short Answer. Please be as brief as possible.
1. How do the carbohydrates attached to ECM glycoproteins differ from those that compose the GAGs
and are attached to the proteoglycans? (1 point)
2. An enzyme that requires metal ions as a cofactor is called a(n) _________________. (1 point)
3. To what part of an enzyme does a noncompetitive inhibitor bind? (1 point)
4. The primary stroma of the chick cornea has no cells within it. Yet the secondary stroma,
which is derived from the primary stroma contains fibroblast cells flattened between layers of
collagen. In order for cells to migrate into the stroma, it must swell first by the secretion of a
GAG into its space. Later, the swelling must be reversed. How is this accomplished? (1 point)
5. What is the advantage of negative cooperativity? (1 point)
6. You place cells in a culture dish coated with extracellular matrix material. Normally, they will
bind to the culture dish’s surface. You add RGD tripeptides along with the cells, and they do not
stick to the dish. What proteins must be embedded in their cell membranes? (1 point)
Biology 362
Cell Biology
Joel Piperberg
April 17 - 19, 2018
Second Exam
Page # 7
Name ___________________________________
7. On what kind of molecule would you find a carbohydrate chain with a repeating disaccharide
sequence that is unbranched and of fairly large size often comprising a significant part of the
molecular weight of the molecule of which it is a part? (1 point)
8. What protein is part of the basement membrane and directs the migration of cells in the
mammalian embryo? What is another name for the basement membrane? (2 points)
9. What is a hydrolase? (1 point)
IV. Short Answer Bonus
1. Sometimes two amino acid R groups projecting into an enzyme's active site 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. What type of signaling is typified by the drawing below? (1 point)
Receptor 1
Effector 1
Effector 2
Effector 3
Effector 4
3. What are the two major characteristics of a cascade? (2 points)
4. What is the name of the protein domain that binds to the phosphorylated tyrosine of an
activated insulin receptor? (1 point)
5. What is the name of Bart’s teacher on The Simpsons? (1 point)
Biology 362
Cell Biology
Joel Piperberg
April 17 - 19, 2018
Second Exam
Page # 8
Name ___________________________________
6. Supposedly every track on Coldplay's Viva laVida CD is about what historical figure? (1 point)
7.
a. Name a molecule that activates protein kinase C? (1 point)
b. What enzyme breaks glycogen into glucose? (1 point)
8. What is the name of a molecule that is phosphorylated by an RTK? (1 point)
9. What breaks down cGMP? (1 point)
10. When multiple receptors affect one effector, this arrangement is called _________.
(1 point)
11. What is a glycan? (1 point)
12. What is made up of the cell coat and the fuzzy layer? (1 point)
13. What is the name of the organized network of extracellular materials found beyond immediate
vicinity of membrane? (1 point)
14. Briefly describe an experiment that would demonstrate that fibronectin plays an important
role in development. (2 points)
15. What used to be known as mucopolysaccharides? (1 point)
16. Describe the steps involved in the mechanism of steroid hormone action. (3 points)
Biology 362
Joel Piperberg
Second Exam
Name ___________________________________
17. a. What activates guanylate cyclase?
Cell Biology
April 17 - 19, 2018
Page # 9
b. What activates glycogen phosphorylase?
c. What gets rid of activated glycogen phosphorylase after a hormone leaves its receptor and
the hormone response needs to be ramped down?
d. What kind of enzyme phosphorylates IRSs?
e. What G protein has been implicated in approximately 40% of human cancers?
f. What is the name of a series of reactions in which each reaction triggers the next and the
response is magnified with each step?
(2.5 points)
Biology 362
Joel Piperberg
Second Exam
Name ___________________________________
Cell Biology
April 17 - 19, 2018
Page # 10