The Main Circuit: Microtubules Function

If a cell needs to transport a vesicle from the Golgi apparatus to the cell membrane, then it requires a physical track to move along. If microtubules act as these tracks, then the primary microtubules function is the movement of organelles and vesicles.

If the structural building blocks of these fibers are protein dimers, and these dimers assemble into a hollow cylinder, then the protein is identified as tubulin.

If a cell is dividing and needs to move chromosomes to opposite poles, then it must use a mechanical force. If microtubules grow and attach to chromosomes to move them, then their function involves forming spindle fibers.

If an axon is very long and nutrients are made in the cell body, then the cell needs a long-distance transport system. If microtubules act as the highway for motor proteins, then they are critical for carrying those nutrients.

If cargo needs to be moved across the cell, then it needs a protein "engine" to carry it. If these engines use microtubules as a track, then motor proteins like kinesin effectively walk along them.

If the cytoskeleton contains microfilaments, intermediate filaments, and microtubules, then they are categorized by size. If microtubules have a diameter of about 25 nanometers, then they are actually the thickest, not the thinnest.

If a highway is a permanent or semi-permanent path used to get from point A to point B efficiently, then the cell's internal transport tracks serve the same purpose. If microtubules provide these paths, then the analogy is accurate.

If cilia and flagella are used for movement and require a rigid internal scaffold, and if spindle fibers move chromosomes, then all three structures must be composed of microtubules.

If a cell needs to constantly remodel its internal structure, then its highways must be able to assemble and disassemble quickly. If this shifting state is observed, then it is termed dynamic instability.

If microtubules are built from directional tubulin subunits, then the resulting tube will have two distinct ends. If the ends behave differently, then one is designated "plus" (fast-growing) and the other "minus."

If different motor proteins are "programmed" to walk in specific directions, then they are categorized by their destination. If kinesin is the protein that moves toward the periphery, then it is the "plus-end" directed motor.

If microtubules are a defining feature of the complex internal skeleton of eukaryotes, then they are generally absent in prokaryotes. If bacteria have similar proteins, then they are distinct from the tubulin-based microtubules found in grade-level biology.

If kinesin moves toward the "plus" end, then the cell needs a different protein to move things back the other way. If dynein moves toward the centrosome, then it is moving toward the minus end.

If microtubules are described as "tubules," then they must be hollow tubes rather than solid ropes. If they are hollow tubes made of tubulin, then they provide compression resistance rather than tension.

If microtubules need an organized starting point to grow outward, then they must originate from a microtubule-organizing center (MTOC). If the main MTOC in animal cells is the centrosome, then that is the starting point.

If a cell is subjected to external pressure and needs to keep its 3D shape, then it needs a rigid internal skeleton. If microtubules are the thickest and most rigid part of the cytoskeleton, then they function as the primary structural frame.

If a motor protein is performing mechanical work to move a vesicle, then it must consume cellular fuel. If ATP is the primary energy currency of the cell, then it is the fuel used for this movement.

If cancer is characterized by rapid, uncontrolled cell division, then stopping the machinery of division can treat it. If microtubules are necessary to pull chromosomes apart, then a drug that breaks microtubules will stop the cancer from spreading.

If you look at a cross-section of a flagellum under a microscope, then you see nine pairs of microtubules surrounding two single microtubules in the center.

If the highway is made of tubulin subunits, then a chemical that prevents them from sticking will cause the highways to fall apart. If the highways disappear, then transport and division will cease.