MEDICAL PHYSIOLOGY

Detailed explanation-1: -Each actin monomer (globular [G] actin) has tight binding sites that mediate head-to-tail interactions with two other actin monomers, so actin monomers polymerize to form filaments (filamentous [F] actin) (Figure 11.2).

Detailed explanation-2: -ATP-bound G-actin is the normal substrate for filament formation. It may be induced to polymerize to ATP-containing F-actin, which is energetically favored under physiological conditions. However, F-actin is a slow ATPase, such that the filament soon contains just ADP. ADP F-actin is less stable than ADP G-actin.

Detailed explanation-3: -Actin filaments (F-actin) are linear polymers of globular actin (G-actin) subunits and occur as microfilaments in the cytoskeleton and as thin filaments, which are part of the contractile apparatus, in muscle and nonmuscle cells (see contractile bundles).

Detailed explanation-4: -3.2. 2.1 Actin. F-actin are polarized polymers that elongate at the barbed end and disassemble at the pointed end.

Detailed explanation-5: -Of the three types of protein fibers in the cytoskeleton, microfilaments are the narrowest. They function in cellular movement, have a diameter of about 7 nm, and are made of two intertwined strands of a globular protein called actin. For this reason, microfilaments are also known as actin filaments.