Question

24.       Actin filament treadmilling is characterized by:

A.         the addition of subunits to the plus end and simultaneous loss of subunits from the minus end

B.         the rapid loss of subunits from the plus end only

C.        the addition of cytoskeletal branches by the ARP complex

D.        none of the above

Answer _________

25.       During neutrophil cell migration or chemotaxis, Rac activation dominates at the front of the cell, here Rac functions to...

A.         directly bind GPCRs

B.         promote Arp2/3 activity downstream of WASp family proteins

C.        promote actin-myosin contraction

D.        activate Rho GTPases

E.         none of the above

Answer _________

Answer 1

24. (A) The addition of subunits to the plus end and simultaneous loss of subunits from the minus end.

Actin filament ahs two ends, plus end and minus end which differ in dynamics of adding and removing of subunits. The elongation of the Actin filament occurs when G actin is bound to the ATP presnt on the filament. It is easier for G actin to bind with ATP at plus end rather than minus end. This difference occurs becasue the elongation at minus end requirs the conformational change in the subunits to associate with ATP.