Following statements are regarding to the mechanism of thick filament regulation.

A. In vertebrate smooth muscle, phosphorylation of the myosin regulatory light chain (LC) activates contraction.

B. At Ca2+ concentrations of more than 10−6 M, the regulatory light chain is not phosphorylated, and the myosin adopts a folded conformation.

C. When the Ca2+ level rises, Ca2+ binds calmodulin (CaM), which undergoes a conformational change (CaM*). The CaM*-Ca2+ complex binds and activates myosin light chain kinase (MLC kinase), which then phosphorylates the myosin LC. This phosphorylation event unfolds the myosin II, which is now active and can assemble into bipolar filaments to participate in contraction.

D. When the Ca2+ levels drop, the myosin LC is dephosphorylated by myosin light-chain (MLC) phosphatase, which is dependent on Ca2+ for activity, causing muscle relaxation.

Which of the following combination is correct?

#Question id: 2575

#Unit 2. Cellular Organization

NMR studies of the pectin molecules indicate that, which one is not true for pectin ?

#Question id: 2576

#Unit 2. Cellular Organization

What effect will addition of AMP-PNP have on axonal transport?

#Question id: 2577

#Unit 2. Cellular Organization

Which of the following occur(s) during prophase?

a. Kinetochores capture microtubule (+) ends.

b. Chromosomes move poleward.

c. Chromosomes align on the spindle equator.

d. Centrosomes separate and the spindle begins to form.

e. Chromosome condensation begins.

#Question id: 2578

#Unit 2. Cellular Organization

Following statements are regarding to proteins which involve actin filament assembly.

A. To nucleate the assembly of branched actin, Arp2/3 needs to be activated by interacting with a nucleation promoting factor (NPF), in addition to associating with the side of a pre-existing actin filament.

B. The NPF WASp is inactive due to an intramolecular interaction that masks the WCA domain.

C. Two NPFs each bind an actin subunit at their WH2 domains, and together, they activate the Arp2/3 complex through its interaction with their connector and acidic domains.

D. The NPF WASp is activated by a coincidence detection mechanism by which intramolecular interaction in WASp is relieved, allowing the W domain to bind actin and the acidic A domain to activate the Arp2/3 complex.

Which of the following statements represents regulation of the Arp2/3 complex by NPF?

#Question id: 2579

#Unit 2. Cellular Organization

Match the following proteins (Column I) with their functions (Column II) during cell organization and movement.

Which of the following is correct?

#Question id: 2580

#Unit 2. Cellular Organization

Following statements are regarding to mechanism of kinesin-1 movement.

A. Initially leading head tightly bound to the microtubule and not bound by any nucleotide, while the trailing head is weakly bound to the microtubule and has ADP bound.

B. Binding of ATP induces a conformational change causing the linker to swing forward and dock into the head. This motion swings the former trailing head to become the leading head.

C. Binding of ATP induces a conformational change causing the linker to swing forward and dock into the head. This motion swings the former leading head to become the trailing head.

D. When leading head releases ADP and coordinately the trailing head hydrolyzes ATP to ADP + Pi. Pi is released and the linker becomes undocked.

E. When trailing head releases ADP and coordinately the leading head hydrolyzes ATP to ADP + Pi. Pi is released and the linker becomes undocked.

Which of the following combination is correct?