MCB 150 FINAL EXAM UPDATED QUESTIONS
AND CORRECT ANSWERS
Question:
1. Which of the following drugs works by stabilizing microtubules rather than blocking their formation?
A. Taxol
B. Vinblastine
C. Colchicine
D. Vincristine
E. Colcemid
Answer:
A. Taxol
Question:
2. Which one of the following statements about microtubules is correct?
A. Tubulin dimers with nucleoside diphosphates in their nucleotide binding site(s) have a lower affinity for
each other than tubulin dimers with nucleoside triphosphates in their nucleotide binding site(s).
B. In vivo, polymerization of microtubules typically occurs at the minus end because the plus end is
anchored.
C. Myosin is a motor protein that moves toward the plus end of microtubules.
D. Only the alpha subunit of a tubulin dimer has a nucleotide binding site.
E. ATP is the nucleotide that occupies the nucleotide binding site(s) of tubulin dimers.
Answer:
A. Tubulin dimers with nucleoside diphosphates in their nucleotide binding site(s) have a lower affinity for
each other than tubulin dimers with nucleoside triphosphates in their nucleotide binding site(s).
Question:
3. Which of the following is a property of microtubules, but not of actin?
A. In vitro, both ends can show dynamic growth
B. Can be used for vesicle transport
C. Subunits are dimeric
D. Can form stable arrangements to support cell projections
E. Polarity at filament ends
Answer:
C. Subunits are dimeric. Microtubule subunits (tubulin) are dimeric, while actin filament subunits
(G-actin) are monomeric.
Question:
4. Identify if the following statements regarding microtubule function in a cell are true or false. Choices:
True, False.
1. Microtubules are completely unchanging, stable structures.
2. Cilia are extensions of cytoplasm stabilized by microtubules.
3. During interphase, microtubules typically do not reach the cell membrane.
4. Microvilli are the same as flagella.
,Answer:
1. False
2. True
3. True
4. False
Question:
5. Decide if the following statements are true or false. Choices: True, False.
1. Tubulin subunits have ATP-binding sites.
2. Colcemid could be used as a muscle relaxant; it would relieve tension by promoting the degradation of
actin filaments.
3. In vivo, microtubules often have their plus end anchored into the MOC.
4. Vinblastin would be likely to affect a human embryo more severely than a grown person.
Answer:
1. False. Tubulin subunits have GTP-binding sites.
2. False. Colcemid could be used in the lab to induce depolymerization of microtubules and
non-specifically affects all microtubules.
3. False. In vivo, microtubules have their minus ends anchored into the MTOC.
4. True. Vinblastin induces depolymerization of microtubules and targets rapidly-dividing cells.
Question:
6. Treatment of a cell with the drug Colchicine will:
A. promote microtubule depolymerization because the colchicine will bind the microtubule ends.
B. stabilize microtubule length because colchicine will bind the microtubule ends.
C. promote microtubule depolymerization because the effective concentration of tubulin will be too low to
sustain polymerization.
D. stop microtubule depolymerization because the free tubulin will bind the colchicine.
E. promote microtubule polymerization because the colchicine will bind the microtubule ends.
Answer:
C. promote microtubule depolymerization because the effective concentration of tubulin will be too low to
sustain polymerization.
Question:
7. Identify if each of the following statements are true or false. Choices: True, False.
1. Microtubules and tubulin building blocks both have polarity.
2. If the concentration of GTP-bound tubulin is increased, depolymerization is more likely to occur.
3. The addition of ATP to tubulin will increase the concentration of ATP bound tubulin and the
microtubule will polymerize.
4. Assembly and disassembly of microtubules is typically fastest at the plus end in a living cell.
Answer:
1. True.
2. False. If the concentration of GTP-bound tubulin is increased, polymerization is more likely to occur.
3. False. The addition of GTP to tubulin will increase the concentration of GTP-bound tubulin and the
microtubule will polymerize.
4. True. (since the minus end is bound to the MTOC)
,Question:
8. Which of the following statements is TRUE?
A. Axons and dendrites are examples of microvilli.
B. Axons and dendrites are important for the motility of nerve cells.
C. Microtubules are found in a 9+2 pattern in axons but not dendrites.
D. Axons and dendrites are anchored in the centrosome of nerve cells.
E. Axons and dendrites are the cytoplasmic extensions of nerve cells.
Answer:
E. Axons and dendrites are the cytoplasmic extensions of nerve cells. Axons are not the same as axonemes.
Question:
9. Which of the following proteins is responsible for the movements of cilia?
A. Kinesin
B. G-actin
C. Myosin
D. F-actin
E. Dynein
Answer:
E. Dynein
Question:
10. From where do microtubules most specifically originate in an animal cell?
A. Centrioles
B. Cytoplasm
C. The cell
D. Centromere
E. Pericentriolar material
Answer:
E. Pericentriolar material Microtubules emanate from the PCM.
Question:
11. Identify whether each of the following statements about microtubules is true or false. Choices: True,
False.
1. Both the alpha and the beta subunit of the microtubules have a GTP binding site.
2. Microtubules are the largest of the cytoskeletal elements, made up of 25 protofilaments.
3. In a microtubule, the rate of polymerization in vitro is typically faster at the plus end.
4. Assembly and disassembly is normally fastest at the plus end in vivo.
Answer:
1. True.
2. False. Microtubules are the largest of the cytoskeletal elements, made up of 13 protofilaments.
3. True.
4. True.
, Question:
12. The behavior in which a microtubule alternates between periods of growth and shrinkage is most
accurately called:
A. recycling.
B. dynamic instability.
C. cytoplasmic streaming.
D. an equilibrium state.
E. treadmilling.
Answer:
B. dynamic instability.
Question:
13. The beating of cilia and flagella occurs by means of _______-based _______.
A. myosin; microtubule contraction
B. dynein; microtubule sliding
C. dynein; microtubule contraction
D. kinesin; microtubule sliding
E. myosin; microfilament sliding
Answer:
B. dynein; microtubule sliding
Question:
14. Cytoplasmic dynein plays a key role in the positioning of which organelle?
A. Mitochondrion
B. Chloroplast
C. Lysosome
D. Golgi apparatus
E. Endoplasmic reticulum
Answer:
D. Golgi apparatus
Question:
15. Microtubules are not the basis for:
A. cytokinesis of animal cells.
B. movement of chromosomes during mitosis.
C. movement of cilia and flagella.
D. transport of membranous vesicles in the cytoplasm.
E. Microtubules are the basis for all of the above functions.
Answer:
A. cytokinesis of animal cells.
Question:
16. Microtubules are assembled from:
A. dimers of α- and β-tubulin.
B. alternating α-tubulin dimers and β-tubulin dimers.
C. α-tubulin dimers.
D. β-tubulin dimers.
E. Some microtubules are assembled from α-tubulin, others are assembled from β-tubulin.
AND CORRECT ANSWERS
Question:
1. Which of the following drugs works by stabilizing microtubules rather than blocking their formation?
A. Taxol
B. Vinblastine
C. Colchicine
D. Vincristine
E. Colcemid
Answer:
A. Taxol
Question:
2. Which one of the following statements about microtubules is correct?
A. Tubulin dimers with nucleoside diphosphates in their nucleotide binding site(s) have a lower affinity for
each other than tubulin dimers with nucleoside triphosphates in their nucleotide binding site(s).
B. In vivo, polymerization of microtubules typically occurs at the minus end because the plus end is
anchored.
C. Myosin is a motor protein that moves toward the plus end of microtubules.
D. Only the alpha subunit of a tubulin dimer has a nucleotide binding site.
E. ATP is the nucleotide that occupies the nucleotide binding site(s) of tubulin dimers.
Answer:
A. Tubulin dimers with nucleoside diphosphates in their nucleotide binding site(s) have a lower affinity for
each other than tubulin dimers with nucleoside triphosphates in their nucleotide binding site(s).
Question:
3. Which of the following is a property of microtubules, but not of actin?
A. In vitro, both ends can show dynamic growth
B. Can be used for vesicle transport
C. Subunits are dimeric
D. Can form stable arrangements to support cell projections
E. Polarity at filament ends
Answer:
C. Subunits are dimeric. Microtubule subunits (tubulin) are dimeric, while actin filament subunits
(G-actin) are monomeric.
Question:
4. Identify if the following statements regarding microtubule function in a cell are true or false. Choices:
True, False.
1. Microtubules are completely unchanging, stable structures.
2. Cilia are extensions of cytoplasm stabilized by microtubules.
3. During interphase, microtubules typically do not reach the cell membrane.
4. Microvilli are the same as flagella.
,Answer:
1. False
2. True
3. True
4. False
Question:
5. Decide if the following statements are true or false. Choices: True, False.
1. Tubulin subunits have ATP-binding sites.
2. Colcemid could be used as a muscle relaxant; it would relieve tension by promoting the degradation of
actin filaments.
3. In vivo, microtubules often have their plus end anchored into the MOC.
4. Vinblastin would be likely to affect a human embryo more severely than a grown person.
Answer:
1. False. Tubulin subunits have GTP-binding sites.
2. False. Colcemid could be used in the lab to induce depolymerization of microtubules and
non-specifically affects all microtubules.
3. False. In vivo, microtubules have their minus ends anchored into the MTOC.
4. True. Vinblastin induces depolymerization of microtubules and targets rapidly-dividing cells.
Question:
6. Treatment of a cell with the drug Colchicine will:
A. promote microtubule depolymerization because the colchicine will bind the microtubule ends.
B. stabilize microtubule length because colchicine will bind the microtubule ends.
C. promote microtubule depolymerization because the effective concentration of tubulin will be too low to
sustain polymerization.
D. stop microtubule depolymerization because the free tubulin will bind the colchicine.
E. promote microtubule polymerization because the colchicine will bind the microtubule ends.
Answer:
C. promote microtubule depolymerization because the effective concentration of tubulin will be too low to
sustain polymerization.
Question:
7. Identify if each of the following statements are true or false. Choices: True, False.
1. Microtubules and tubulin building blocks both have polarity.
2. If the concentration of GTP-bound tubulin is increased, depolymerization is more likely to occur.
3. The addition of ATP to tubulin will increase the concentration of ATP bound tubulin and the
microtubule will polymerize.
4. Assembly and disassembly of microtubules is typically fastest at the plus end in a living cell.
Answer:
1. True.
2. False. If the concentration of GTP-bound tubulin is increased, polymerization is more likely to occur.
3. False. The addition of GTP to tubulin will increase the concentration of GTP-bound tubulin and the
microtubule will polymerize.
4. True. (since the minus end is bound to the MTOC)
,Question:
8. Which of the following statements is TRUE?
A. Axons and dendrites are examples of microvilli.
B. Axons and dendrites are important for the motility of nerve cells.
C. Microtubules are found in a 9+2 pattern in axons but not dendrites.
D. Axons and dendrites are anchored in the centrosome of nerve cells.
E. Axons and dendrites are the cytoplasmic extensions of nerve cells.
Answer:
E. Axons and dendrites are the cytoplasmic extensions of nerve cells. Axons are not the same as axonemes.
Question:
9. Which of the following proteins is responsible for the movements of cilia?
A. Kinesin
B. G-actin
C. Myosin
D. F-actin
E. Dynein
Answer:
E. Dynein
Question:
10. From where do microtubules most specifically originate in an animal cell?
A. Centrioles
B. Cytoplasm
C. The cell
D. Centromere
E. Pericentriolar material
Answer:
E. Pericentriolar material Microtubules emanate from the PCM.
Question:
11. Identify whether each of the following statements about microtubules is true or false. Choices: True,
False.
1. Both the alpha and the beta subunit of the microtubules have a GTP binding site.
2. Microtubules are the largest of the cytoskeletal elements, made up of 25 protofilaments.
3. In a microtubule, the rate of polymerization in vitro is typically faster at the plus end.
4. Assembly and disassembly is normally fastest at the plus end in vivo.
Answer:
1. True.
2. False. Microtubules are the largest of the cytoskeletal elements, made up of 13 protofilaments.
3. True.
4. True.
, Question:
12. The behavior in which a microtubule alternates between periods of growth and shrinkage is most
accurately called:
A. recycling.
B. dynamic instability.
C. cytoplasmic streaming.
D. an equilibrium state.
E. treadmilling.
Answer:
B. dynamic instability.
Question:
13. The beating of cilia and flagella occurs by means of _______-based _______.
A. myosin; microtubule contraction
B. dynein; microtubule sliding
C. dynein; microtubule contraction
D. kinesin; microtubule sliding
E. myosin; microfilament sliding
Answer:
B. dynein; microtubule sliding
Question:
14. Cytoplasmic dynein plays a key role in the positioning of which organelle?
A. Mitochondrion
B. Chloroplast
C. Lysosome
D. Golgi apparatus
E. Endoplasmic reticulum
Answer:
D. Golgi apparatus
Question:
15. Microtubules are not the basis for:
A. cytokinesis of animal cells.
B. movement of chromosomes during mitosis.
C. movement of cilia and flagella.
D. transport of membranous vesicles in the cytoplasm.
E. Microtubules are the basis for all of the above functions.
Answer:
A. cytokinesis of animal cells.
Question:
16. Microtubules are assembled from:
A. dimers of α- and β-tubulin.
B. alternating α-tubulin dimers and β-tubulin dimers.
C. α-tubulin dimers.
D. β-tubulin dimers.
E. Some microtubules are assembled from α-tubulin, others are assembled from β-tubulin.
