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Biology 263
Cell Biology
Joel Piperberg
April 12, 2010
Third 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. L —> N
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?
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. 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. c and e
b. LDL receptors bind it too tightly.
e. Receptors for LDL do not bind to coated pits.
c. Receptors for LDL are not made.
4. Coated pits are a site at which _______ can occur.
a. receptor-mediated endocytosis
c. fluid-phase endocytosis
b. absorptive endocytosis
d. a and c
e. adsorptive exocytosis
5. An enzyme that requires a permanently associated metal ion and organic component that
assists in its reaction mechanism might be said to require a ___________.
a. cofactor b. coenzyme
c. conjugated nucleotide
d. prosthetic group
e. a and d
6. Which of the following directly produces a second messenger?
a. phosphorylase kinase b. adenylate lipase C c. adenylate cyclase d. c and e e. protein kinase A
7. 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
8. The Na - K pump makes the cell interior ___ because it pumps ____ Na out for every ____ K
pumped in.
a. neutral; 3; 3 b. negative; 2; 3 c. positive; 2; 3 d. negative; 3; 2
e. positive; 3; 2
Biology 263
Cell Biology
Joel Piperberg
April 12, 2010
Third Exam
Page # 2
Name ___________________________________
9. You are studying a membrane transport molecule. You have discovered that it transports Cland glucose. You have prepared inside-out and right-side out vesicles. If both of the above
substances are found on the same side of either type of vesicle transport is not seen to occur.
If, on the other hand, glucose is placed outside and Cl- is placed inside 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 that would work if Cl- and glucose were placed outside the inside-out vesicles.
c. It is a symport that 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
10. Some membrane transport proteins allow molecules to leave or enter cells by moving down
the concentration gradient through a passage in the transport protein. This can occur as long as
the molecule to be transported can fit through the passage and has a charge that will allow it to
pass through. Such a molecule is called a(n) ________ protein.
a. intrinsic
b. a, c and d
c. transmembrane d. channel e. carrier
11. Some transport proteins convey molecules through a membrane and up a concentration
gradient by binding to the molecules. These transport proteins have some of the properties of
enzymes. What type of transport is not coordinated by these proteins?
a. active transport
c. passive diffusion
e. b and c
b. facilitated diffusion
d. carrier-mediated transport
12. A channel protein will sometimes allow things to pass through at all times. At other times,
molecules or ions may only pass through a channel only at certain times or in response to certain
stimuli. Such a transport protein (described in the second sentence) is called a ________.
a. broken channel b. gated channel c. gated carrier d. marked channel e. extrinsic protein
13. Active transport is characterized by _____________.
a. transport against a concentration gradient
b. transport down a concentration gradient
c. the requirement for energy often in the form of ATP hydrolysis
14. What is an electrochemical gradient?
a. a gradient in charge and molecular weight
b. a gradient in molecular weight alone
c. a gradient in concentration
d. a and c
e. b and c
d. a gradient in molecular weight & concentration
e. a gradient in charge and concentration
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
Biology 263
Cell Biology
Joel Piperberg
April 12, 2010
Third Exam
Page # 3
Name ___________________________________
16. 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
17. 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
18. An inhibitor of an enzyme resembles the natural substrate for that enzyme. Which of the following
is likely to be true?
a. It is a noncompetitive inhibitor. c. Adding more substrate reverses the inhibition.
e. b and c
b. It is a competitive inhibitor.
d. Adding more substrate does not reverse the inhibition.
19. 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
20. 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 rearrangement of the cytoskeleton.
21. After coated vesicles are totally internalized, what happens to the molecules that compose
the coat surrounding it?
a. They are destroyed.
c. They are retrograded.
e. They are recycled to another coated pit.
b. They are altered.
d. They are degraded.
22. According to the Second Law of Thermodynamics, ___________.
a. energy cannot be created or 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 decreases
23. 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
24. 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
25. 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
Biology 263
Joel Piperberg
Third Exam
Name ___________________________________
26. Which of the following is directly activated by cAMP?
a. phosphodiesterase b. phosphatase c. protein kinase A
Cell Biology
April 12, 2010
Page # 4
d. RTKs
e. phosphorylase kinase
27. 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
28. Which of the following could be true if an active enzyme is inhibited at its active site with a
molecule called P2?
a. P2 would 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. Less water would have to be made available.
29. An enzyme is inhibited at its allosteric 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 allosteric site.
b. P3 would be similar in structure to the substrate. e. P3 concentration is lower than that of substrate.
c. P3 is likely to differ from the substrate in structure.
30. Most receptor mediated endocytosis begins at a site called a ____________.
a. fuzzy coat b. coated pit
c. coated vesicle
d. clathrin
e. inpocketing
31. 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 increase the binding activity of other active sites.
d. Substrate bound at one active site decrease the binding activity of other active sites.
e. b and c
32. 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.
33. A reaction that proceeds with a _____ of free energy in the system is called an _____ reaction.
a. loss; exergonic
c. a and b
e. loss; exothermic
b. gain; endergonic
d. gain; endothermic
34. 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 and c
c. by adding some product B
Biology 263
Joel Piperberg
Third Exam
Name ___________________________________
35. 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 raising the reaction rate
e. none of the above
Cell Biology
April 12, 2010
Page # 5
36. 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. straining a bond
e. transient formation of ionic bonds
c. weakening of bonds by electrophilic attack
37. 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 electromagnetically
c. works by locally defolding and refolding around the substrate
d. possesses a rigid active site that can distinguish minor differences between potential substrates
e. is made of petroleum products
38. Which of the following represents potential energy?
a. water behind a dam
c. a boulder rolling down a hill
b. a tank filled with gasoline.
d. a and b
e. a thrown ball
39. The abbreviation that represents a change in the entropy of a system is ______.
a. TS
b. S
c. G
d. H
e. H
40. 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.
41. An open system _____________.
a. exchanges matter with the surroundings
b. can exchange energy with its surroundings
c. a and b
d. exchanges nothing with the surroundings
e. exchanges no matter with its surroundings
42. Which of the following cannot be an enzyme?
a. b, c and d
b. a protein
c. RNA
d. amylase
e. amylose
43. Peptide hormones can exert their effects by ___________.
a. inactivating active enzymes
c. activating receptor tyrosine kinases
e. a, b and c
b. indirectly activating G proteins
d. causing the deacetylation of enzymes
Biology 263
Joel Piperberg
Third Exam
Name ___________________________________
44. At what time do living organisms attain equilibrium?
a. at birth
b. at death
c. at adolescence
d. never
45. Which of the following acts at the cell surface?
a. steroid hormones b. peptide hormones c. calmodulin
Cell Biology
April 12, 2010
Page # 6
e. until they die
d. epinephrine
e. b and d
46. According to the First Law of Thermodynamics, _____________.
a. the universe's entropy is increasing
d. energy cannot be created
b. d and e
e. energy can be transduced
c. matter is constant
47. 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
48. Which of the following would not explain a drop in the rate of product production?
a. products changing the pH of the medium
b. d and e
c. heat denaturing 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
49. You homogenize the liver from a rat. After centrifugation to isolate the particulate fraction
in the pellet, you 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.
50. You treat the pellet from #49 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 #49? What happens to the activity of different enzymes below in the supernatant?
a. Glycogen phosphorylase activity rises.
d. a and e
b. Phosphoribosylkinase activity drops.
e. Glycogen synthase activity drops.
c. Protein kinase activity decreases.
51. The initial supernatant from #49 is treated directly with cyclic AMP. What happens to
enzyme activities in the supernatant?
a. Phosphorylase kinase activity increases.
d. Glycogen synthase activity stays the
b. Glycogen phosphorylase activity does not change. e. a and c
c. Protein kinase activity rises.
52. What happens to glycogen phosphorylase activity in the initial supernatant from #49 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.
Biology 263
Cell Biology
Joel Piperberg
April 12, 2010
Third Exam
Page # 7
Name ___________________________________
III. Short Answer. Please be as brief as possible.
1. What is the thermodynamic term that describes the heat or energy content of a system? (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. ________________ is energy that is stored in an object or system by virtue of its position or the
energy content stored within its bonds. (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. The reaction G + S <—> K + L is highly endothermic and results in a decrease in entropy? Is
the G of this reaction positive, negative or 0? How do you know? (2 points)
3. What are the two major characteristics of a cascade? (2 points)
4. What is the name of the short amino acid sequences within proteins that are recognized by
protein kinases and to which those protein kinases add a phosphate group? (1 point)
5. What is the name of Bart’s teacher on The Simpsons? (1 point)
6. Supposedly every track on Coldplay's Viva laVida CD is about what historical figure? (1 point)
Biology 263
Joel Piperberg
Third Exam
Name ___________________________________
7. a. Name a molecule that activates a protein kinase A? (1 point)
Cell Biology
April 12, 2010
Page # 8
b. What enzyme polymerizes glucose into glycogen? (1 point)
8. What is a "dead-man switch" with respect to a cell? Name one. Explain how the "dead-man
switch" you named fulfills its role as a "dead-man switch" in a hormonal response. (3 points)
9. What is the three-legged trimer that serves as the structural subunit of the clathrin coat? (1 point)
10. What two features must coupled reactions have? (2 points)
11. What is the advantage of negative cooperativity? (1 point)
12. Since _______ organisms are ______ systems, they exhibit steady state instead of ________.
(3 points)