MCB 150 FINAL COMPREHENSIVE QUESTIONS
AND COMPLETE SOLUTIONS
◉ 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).
◉ 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.
◉ 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
,◉ 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.
◉ 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.
◉ 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.
AND COMPLETE SOLUTIONS
◉ 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).
◉ 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.
◉ 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
,◉ 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.
◉ 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.
◉ 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.
