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greymacaw773Lv1

28 Sep 2019

Dynamic instability causes microtubules to grow and shrink rapidly. Consider a microtubule that is in its shrinking phase. Why is it shrinking, and what must happen at the end of the microtubule for it to stop shrinking and start growing?

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Sixta KovacekLv2

28 Sep 2019

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1. Kinesin-1 motors can move long distances on microtubule tracks without dissociating. By contrast, myosin II motors in skeletal muscle take only one or a few steps before letting go. What is most likely the difference between these two motors that allow two different types of movement?

A. Differences in length of the stalk of each respective motor allow for differences in step size

B. Differences in ATP versus GTP hydrolysis alter the motor head movement along filaments

C. Actin filaments are smaller in diameter and have less space for movement

D. Binding affinity of the Kinesin-1 motor head to microtubules is high, whereas binding affinity of the myosin II motor head to actin filaments is low

E. Microtubules are larger in diameter and have more space for movement

2. Dynamic instability causes microtubules either to grow or to shrink rapidly. What is the most likely reason for a microtubule to undergo rapid growth?

A. GTP hydrolysis exceeds the rate of heterodimer addition

B. GTP hydrolysis of alpha tubulin causes an outward bend in the heterodimer conformation

C. A low concentration of tubulin heterodimers are in solution

D. Heterodimer addition exceeds the rate of GTP hydrolysis

E. Increased trafficking of microtubule motor proteins favors stability

3. There are no known motor proteins that move on intermediate filaments (IFs). What property of intermediate filaments would most likely explain the lack of motor proteins?

A. Tissue specific expression of IFs prevent a single type of motor protein to evolve over time

B. Lateral bundling of IFs prevent motor movement

C. IFs are less dynamic than microtubules and actin filaments

D. IFs are unpolarized

E. IFs do not bind a nucleotide

4. You discover a mutation that results in less rapid hydrolysis of GTP by the beta-tubulin subunit. What would most likely occur?

A. There would be no change in filament assembly

B. There would be enhanced instability of the microtubule

C. There would be enhanced stability of the microtubule

D. Microtubules would not form

E. There would be enhanced treadmilling

5. Which of the following statements describes common features of cadherins and integrins?

A. They can link to microtubules using specific adapter proteins

B. They mediate heterophillic interactions

C. They achieve high binding affinity through clustering

D. They are responsible for interactions of a cell with the extracellular matrix

E. They are found in the apical plasma membrane of an epithelial cell

6. Intermediate filaments are uniquely non-polar and built by lateral bundling in five steps: 1) synthesis of an alpha-helical monomer, 2) formation of a coiled-coil dimer, 3) formation of a staggered tetramer of two coiled-coil dimers, 4) lateral association of 8 tetramers, and 5) addition of 8 tetramers to a growing filament. At what step is polarity lost?

A. Step 1

B. Step 2

C. Step 3

D. Step 4

E. Step 5

7. Collagenase is an enzyme that breaks peptide bonds in collagen to help destroy extracellular structures. What would be the most likely reason to use collagenase in a cell biology laboratory?

A. Disrupt cadherin interaction with the extracellular matrix

B. Disrupt cell-cell contacts to passage cells in cell culture

C. Dissociate epithelial cells from the underlying basement membrane to separate tissues

D. All of the answers are likely uses for collagenase

E. Lyse cells to expose intracellular proteins and organelles

yellowherring775

You have purified protein you call MAP15. MAP 15 binds totubulin that is GTP-bound tubulin and does not bind to tubulin thatis GDP-bound. You genetically engineered cells to express a greenfluorescent protein (GFP) âtagged version of MAP15. This GRP-MAP15fusion protein does not appear to disrupt the function of MAP15.You use a red fluorescent dye to label the microtubules so that youcan visualize GFP-MAP15 and the microtubules at the same time usingfluorescence microscopy (Note that the red dye does not appear toaffect microtubule structure and function).

A. If you were to polymerize some red-labeled microtubules in adish, would you expect GFP-MAP15 to be associated with one or bothends of a microtubule, with the middle of the microtubule, or beevenly distributed throughout the microtubule? Explain.

B. You examine the red microtubules and GFP-MAP15 in a cell ininterphase. Do you think that you will see GFP-MAP15 associatedwith all microtubules? Explain.

C. If you were to take time-lapse images in which you visualizeonly GFP-MAP15 (and not microtubules), what would you expect tosee? Describe what you think would happen to GFP-MAP over time withrespect to its localization inside of this cell.

taupelouse940

Decide whether each of the following statements are true orfalse and explain why.

A. The structural polarity of all microtubules is such thatÃÂ±-tubulin is exposed at one end and ÃÂ²-tubulin is exposed at theopposite end.

B. The role of ATP hydrolysis in actin polymerization is similarto the role of GTP hydrolysis in tubulin polymerization: both serveto weaken bonds in the polymer and thereby promotedepolymerization.

C. All microtubule organizing centers contain centrioles thathelp nucleate microtubule polymerization.

D. All proteins that bind to the ends of microtubules or actinfilaments cap the ends to prevent futher polymerization.

E. In most animal cells, minus end-directed microtubule motorsdeliver their cargo to the periphery of the cell, whereas plusend-directed microtubule motors deliver their cargo to the interiorof the cell.

F. Cadherins promote cell-cell interactions by binding tocadherin molecules of the same or closely related subtype onadjacent cells.

Lots of points offered. Please help.