#Question id: 2581
#Unit 2. Cellular Organization
Match the following toxins (Column I) with their effects (Column II) on actin.
|
Column I |
Column II |
|
A.
Cytochalasin D |
i. Enhances
nucleation by binding and stabilizing actin dimers and thereby lowering the
critical concentration. |
|
B.
Latrunculin |
ii. Binds at
the interface between subunits in F-actin,
locking adjacent subunits together and preventing actin filaments from
depolymerizing. |
|
C.
Jasplakinolide |
iii.
Depolymerizes actin filaments by binding to the (+) end of F-actin, where it
blocks further addition of subunits. |
|
D. Phalloidin |
iv. Binds and
sequesters G-actin, inhibiting it from adding to a filament end. |
#Question id: 2582
#Unit 2. Cellular Organization
Following statements are regarding to dynamics of actin filaments.
A. When the concentration of G-actin is above the Cc, the filament end will grow; when it is less than the Cc, the filament will shrink.
B. ATP–G-actin is added much faster at the (+) end than at the (−) end, resulting in a lower critical concentration at the (+) end than at the (−) end.
C. At steady state, actin subunits treadmill through a filament. ATP-actin is added at the (+) end, ATP is then hydrolyzed to ADP and Pi, Pi is lost, and ADP-actin dissociates from the (−) end.
D. ATP–G-actin is added much faster at the (-) end than at the (+) end, resulting in a lower critical concentration at the (-) end than at the (+) end.
E. At steady state, actin subunits treadmill through a filament. ATP-actin is added at the (-) end, ATP is then hydrolyzed to ADP and Pi, Pi is lost, and ADP-actin dissociates from the (+) end.
Which of the following statements are correct?
#Question id: 2583
#Unit 2. Cellular Organization
Following statements are regarding to the microtubules.
A. Tubulin is the major structural component of microtubules
B. Microtubule-associated proteins (MAPs) associate with tubulin and help mediate the assembly, dynamics, and function of microtubules.
C. Free tubulin exists as a dimer in which the α-subunit contains a trapped and hydrolyzable GTP and theβ-subunit binds an exchangeable and nonhydrolyzable GTP
D. All microtubules are nucleated from microtubule-organizing centers (MTOCs), and many remain anchored with their (−) ends there. Thus the end away from the MTOC is always the (+) end.
Which of the following statements is incorrect?
#Question id: 2584
#Unit 2. Cellular Organization
The polymerization of pure G-actin in vitro proceeds in three phases.
|
Column I |
Column II |
|
A. nucleation phase |
i. G-actin monomers exchange with subunits at the filament ends, but there is no net change in the total length of filaments |
|
B. elongation phase |
ii. marked by a lag period in which G-actin subunits combine into an oligomer of two or three subunits |
|
C. steady-state phase |
iii. the short oligomer rapidly increases in length by the addition of actin monomers to both of its ends |
Which of the following represent correct match?
#Question id: 2585
#Unit 2. Cellular Organization
Which of the following is the correct sequence that describes the excitation and contraction of a skeletal muscle fiber?
A. Tropomyosin shifts and unblocks the cross-bridge binding sites.
B. Calcium is released and binds to the troponin complex.
C. Transverse tubules depolarize the sarcoplasmic reticulum.
D. The thin filaments are ratcheted across the thick filaments by the heads of the myosin molecules using energy from ATP.
E. An action potential in a motor neuron causes the axon to release acetylcholine, which depolarizes the muscle cell membrane.
#Question id: 2586
#Unit 2. Cellular Organization
Intermediate filaments are the only nonpolar fibrous component of the cytoskeleton and are not associated with motor proteins. Intermediate filaments are built from coiled coil dimers that associate in an antiparallel fashion into tetramers and then into protofilaments, 16 of which make up the filament. There are five major classes of intermediate filament proteins. Match the following proteins (Column I) with their class (Column II).
|
Column I |
Column II |
|
A. Lamins |
a. Class I |
|
B. Keratins |
b. Class II |
|
C. Desmin |
c. Class III |
|
D. Neurofilaments |
d. Class IV |
|
e. Class V |
Which of the following is correct?