Flex and Flow: Microfilaments Explained

If microfilaments are the thinnest fibers of the cytoskeleton, then they must be composed of actin subunits organized into two intertwined strands.

If microfilaments measure approximately 7 nanometers in diameter and microtubules measure 25 nanometers, then microfilaments are indeed the smallest in diameter.

If actin filaments serve as the track and the motor protein pulls against them to shorten the cell, then that motor protein is identified as myosin.

If microfilaments are tension-bearing structures, then they maintain shape and facilitate movement like muscle contraction and cytokinesis, but they do not resist compression or carry oxygen.

If a ring of microfilaments contracts around the middle of a dividing cell, then it creates a "cinching" effect known as a cleavage furrow that eventually splits the cytoplasm.

If actin subunits are added or removed at different rates on each end of the filament, then the fiber possesses structural polarity, creating a plus and minus end.

If "G" stands for globular, then G-actin refers to the free-floating spherical subunits that eventually polymerize to form the F-actin (filament) structure.

If microfilaments form a dense network just under the cell membrane (the cortex), then they act as a supportive mesh that withstands pulling forces to help the cell maintain its 3D integrity.

If a movement involves the rearrangement of actin or the use of myosin, then it includes amoeboid movement, streaming, and crawling; cilia and flagella use microtubules instead.

If the polymerization of actin is an energy-requiring process, then it uses ATP; this distinguishes it from microtubules, which use GTP for assembly.

If a cell needs to crawl, then it must extend a part of itself forward. If microfilaments polymerize rapidly in one direction, then they create the structural extension known as a pseudopodium.

If the fluid inside a large plant cell needs to move in a circle to distribute materials, then microfilament-myosin interactions create the "streaming" motion required for that flow.

If G-actin monomers link together in a specific pattern, then they form a flexible, double-stranded helix with a narrow 7 nm diameter, rather than a hollow tubulin-based tube.

If microvilli are tiny finger-like projections used for absorption, then they need internal support to stay upright. If bundles of microfilaments run through the center, then they act as a skeletal core.

If the cytoskeleton is dynamic, then its components must be able to assemble and disassemble quickly. Since microfilaments are constantly remodeling to help the cell move, they are not static.

If the rate of subunit addition at the plus end matches the rate of loss at the minus end, then the filament appears to move forward through the cytoplasm like a treadmill.

If microfilaments are responsible for maintaining the exterior shape and providing support to the plasma membrane, then they must be concentrated in the outer region called the cortex.

If we compare the two, then microfilaments are uniquely 7 nm thick, composed of actin, and form the cleavage furrow; microtubules are thicker, hollow, and made of tubulin.

If eukaryotic cells share a common internal structural framework to handle movement and shape, then microfilaments are a universal component of that cytoskeleton across all those kingdoms.

If myosin heads attach to actin and perform a power stroke, then the actin filament is pulled toward the center. If the filaments slide past each other, then the overall cell or muscle fiber shortens.