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a curved gamma-tubulin straightens out to provide an anchor

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A living cell uses molecular building blocks to form a microtubule, the stiff, hollow straws that help move things around inside the cytoplasm. In this schematic by Duke cell biologist Harold Erickson, a curved gamma-tubulin straightens out (left) to provide an anchor for the attachment of alpha and beta subunits that form the growing tube (center). When the tube reaches 13 subunits around, it closes to make the cylindrical microtubule (right), which then continues to grow longer by adding subunits on the end, Erickson says. This model remains controversial however, more than ten years after it was first published. (J. Cell Biol 135:5-8; 1996)