A female fly, full of fertilized eggs, is swept by high winds to an island far out to sea. She is the first fly to arrive on this island, and the only fly to arrive in this way. Thousands of years later, her numerous offspring occupy the island, but none of them resembles her. There are, instead, several species each of which eats only a certain type of food. None of the species can fly, for their flight wings are absent, and their balancing organs (i.e., halteres) are now used in courtship displays. The male members of each species bear modified halteres that are unique in appearance to their species. Females bear vestigial halteres. The ranges of all of the daughter species overlap.In each fly species, the entire body segment that gave rise to the original flight wings is missing. The mutation(s) that led to the flightless condition could have

#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?

#Question id: 2581

#Unit 2. Cellular Organization

Match the following toxins (Column I) with their effects (Column II) on actin.

#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?