4. Actin Microfilaments- General Characteristics* Helical polymers of actin protein; two protofilaments* Seven nanometers in diameter* Structurally polar; plus and minus end* Thinner, shorter and more flexible than microtubules;the total length of all actin filaments in most cells is ~ 30x's that of microtubules* Globular actin (G-actin) is basic subunit, highly conserved * In most cases fast reactions to stimuli* Located throughout cell in many arrangements, most highly concentrated in the cell's cortex * Actin filaments found primarily in linear bundles, two-dimensional (sheets, bundles) and three-dimension (gels) networks; rarely occur in isolation
MicrovilliStress fibersLamellipodia, FilopodiaContractile ring
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