Please answer the 3 following question and provide a short reason why you chose
ID: 11345 • Letter: P
Question
Please answer the 3 following question and provide a short reason why you chose your answer.
37. What is the basis for the observation that tubulin dimers can accumulate in GTP-bound state but once
assembled, the GTP becomes hydrolyzed?
A) Stathmin prevents GTP hydrolysis
B) The dimers are accessible to GTP exchange factors but the assembled microtubule is not.
C) MAPs stimulate GTPase activity of tubulin
D) GTPase activity is intrinsic to tubulin but depends on interactions with assembled subunits
E) Accessory proteins prevent hydrolysis of GTP-tubulin dimer
F) None of the above.
38. Due to an error in tube labeling, you mistakenly treat your culture of cells with oubaine, an inhibitor of
the Na+/K+ pump. Once the pump is inactivated, Na+ won’t be pumped out of the cell and K+ won’t be
pumped in. Which of the following is the most accurate series of thoughts going through your mind.
A) Whoops, osmotic crisis. There will be insufficient positive ions in the cell to counter the charge of the
fixed anions. I’ll compensate by transferring the cells to fresh growth medium containing a high
concentration of K+. The K+ will flow in through K+ leak channels and fix the problem.
B) Whoops, osmotic crisis. Water will flow into the cells since they can’t pump out Na+. I’ll compensate
by transferring them to growth medium containing a higher solute concentration.
C) Whoops, osmotic crisis. Water will flow into the cells since they can’t pump out Na+. I’ll compensate
D) Whoops, osmotic crisis. Water will flow out of the cell since the cells can no longer pump out Na+. I’ll
compensate by transferring them to growth medium containing a lower solute concentration.
E) Whoops. Well I guess those cells are goners. Good thing my research advisor has a lot of money so I
can repeat the experiment.
39. Recent studies have shown that under some conditions microtubules can become severed (cut) such
that they are released from the centrosome.
A. What protein complex mediates the attachment of microtubules to the centrosome?
B. What will happen to the large microtubule fragments that are severed from the centrosome?
(choose all correct answers)
a) They will disassemble from the plus end because they will lose their GTP cap more rapidly.
b) They will disassemble from the minus end due to the high off rate of GDP tubulin.
c) They will assemble at the freed minus end because it has a lower Cc for assembly.
d) The length will not necessarily change because minus end assembly/disassembly rates are slow.
e) They will attach to the plus end of another microtubule.
by transferring them to growth medium containing a lower solute concentration.6
Explanation / Answer
Please answer the 3 following question and provide a short reason why you chose your answer.
37. What is the basis for the observation that tubulin dimers can accumulate in GTP-bound state but once
assembled, the GTP becomes hydrolyzed?
A) Stathmin prevents GTP hydrolysis
B) The dimers are accessible to GTP exchange factors but the assembled microtubule is not.
C) MAPs stimulate GTPase activity of tubulin
D) GTPase activity is intrinsic to tubulin but depends on interactions with assembled subunits
E) Accessory proteins prevent hydrolysis of GTP-tubulin dimer
F) None of the above.
38. Due to an error in tube labeling, you mistakenly treat your culture of cells with oubaine, an inhibitor of
the Na+/K+ pump. Once the pump is inactivated, Na+ won’t be pumped out of the cell and K+ won’t be
pumped in. Which of the following is the most accurate series of thoughts going through your mind.
A) Whoops, osmotic crisis. There will be insufficient positive ions in the cell to counter the charge of the fixed anions. I’ll compensate by transferring the cells to fresh growth medium containing a high
concentration of K+. The K+ will flow in through K+ leak channels and fix the problem.
B) Whoops, osmotic crisis. Water will flow into the cells since they can’t pump out Na+. I’ll compensate
by transferring them to growth medium containing a higher solute concentration.
C) Whoops, osmotic crisis. Water will flow into the cells since they can’t pump out Na+. I’ll compensate
D) Whoops, osmotic crisis. Water will flow out of the cell since the cells can no longer pump out Na+. I’ll
compensate by transferring them to growth medium containing a lower solute concentration.
E) Whoops. Well I guess those cells are goners. Good thing my research advisor has a lot of money so I
can repeat the experiment.
39. Recent studies have shown that under some conditions microtubules can become severed (cut) such
that they are released from the centrosome.
A. What protein complex mediates the attachment of microtubules to the centrosome?
B. What will happen to the large microtubule fragments that are severed from the centrosome?
(choose all correct answers)
a) They will disassemble from the plus end because they will lose their GTP cap more rapidly.
b) They will disassemble from the minus end due to the high off rate of GDP tubulin.
c) They will assemble at the freed minus end because it has a lower Cc for assembly.
d) The length will not necessarily change because minus end assembly/disassembly rates are slow.
e) They will attach to the plus end of another microtubule.
by transferring them to growth medium containing a lower solute concentration.6