Chapter 12: Actin Flashcards
Actin exists in cells in two major forms called G actin and F actin. True or False
True
Actin exists in cells in two major forms: G actin (Globular actin) and F actin (Filamentous actin). G actin refers to the monomeric form of actin, which consists of individual actin subunits. F actin, on the other hand, refers to the filamentous form of actin, where multiple G actin subunits polymerize to form long, helical actin filaments.
When is ATP hydrolyzed by actin?
ATP is hydrolyzed by actin during the process of actin polymerization.
ATP hydrolysis by actin occurs during actin polymerization, providing energy for filament assembly and subsequent stability.
To make a branch off an existing actin filament, cells use the protein __________.
Arp2/3
A complex is a protein complex that plays a crucial role in actin filament branching. It promotes the nucleation and formation of new actin filaments at a 70-degree angle to an existing filament. The Arp2/3 complex binds to the side of an existing filament and initiates the formation of a new filament, resulting in the generation of a branched actin network.
The binding of _________ forms bundles of parallel actin filaments.
cross-linking proteins (Villin and fimbrin)
The actin cytoskeleton generates cell movement in the following way: Directed polymerization of actin filaments against the plasma membrane and the interaction of actin filaments and the motor protein myosin. True or False
True.
The actin cytoskeleton generates cell movement through the directed polymerization of actin filaments against the plasma membrane and the interaction of actin filaments with the motor protein myosin.
What is the composition of F-actin filaments?
F-actin filaments, or filamentous actin, have a double helical filament structure.
The polymerized actin subunits (G-actin) assemble in a head-to-tail fashion, forming a double helix structure. This double helix arrangement is often referred to as a twisted or helical polymer of actin filaments.
Under normal physiological conditions during elongation, the barbed end of an actin filament is called __________, is capped by __________ and structurally different than the _________ end.
Positive end; ATP-actin; pointed (minus) end.
In vitro and under steady state conditions, the critical concentration (Cc) of the barbed end of a filament is 0.1 um, and the Cc of the pointed end of this filament is 0.6 um. If the concentration of actin-ATP monomers is 0.3 um, what would happen to this actin filament?
This induces a treadmilling effect where the barbed end will grow and the pointed end will shrink simultaneously because of the difference in their Cc.
What is treadmilling of an actin filament?
The simultaneous polymerization of the barbed end and depolymerization of the pointed end of an actin filament, which creates a constant flux without changing concentrations in the cell. This is regulated by proteins and can only occur when the Concentration is between the Cc of both ends.
Treadmilling of an actin filament refers to a dynamic process in which actin subunits are simultaneously added to one end of the filament (the “plus end”) while being removed from the opposite end (the “minus end”). This results in the overall movement or “treadmill-like” behavior of actin subunits within the filament.
The force generating powerstoke of myosin along an actin filament occurs when myosin _____________.
When myosin releases Pi but is still bond to ADP
