NEET BIOLOGY

Detailed explanation-1: -Individual actin molecules are globular proteins of 375 amino acids (43 kd). 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: -F-actin is a filamentous polymer, composed of G-actin monomers. The F-actin filaments consist of two helical aggregates of G-actin that are twisted around each other, with 13.5 subunits per turn.

Detailed explanation-3: -Actin occurs in two forms: globular actin (G-actin), the free monomeric units of actin, and filamentous actin (F-actin) which is the polymer form. These two forms exist in a dynamic equilibrium with one another as ATP-associated polymerization and depolymerization occur continuously within the cell.

Detailed explanation-4: -Globular (G)-actin, the actin monomer, assembles into polarized filaments that form networks that can provide structural support, generate force and organize the cell. Many of these structures are highly dynamic and to maintain them, the cell relies on a large reserve of monomers.

Detailed explanation-5: -F-actin is composed of two long-pitch helical strands. Interactions between actin subunits of the same strand and the opposing strand-the so-called intrastrand and interstrand interactions, respectively-stabilize the F-actin filament (Fig. 2, Extended Data Figs 4 and 5).