The thylakoid membrane contains light-collecting molecules called pigments, of which chlorophyll is the most common.CYTOSKELETONThe protein fibers of the cytoskeleton provide internal support for cells.•All eukaryotic cells have at least two cytoskeletal elements, microtubules and microfilaments. Animal cells also have intermediate filaments.•These elements are long chains made of protein subunits. They provide structural support and enable the movement of substances within cells.MICROTUBULESMicrotubules are tubelike structures that are polymers of protein dimers.
Microfilament ExampleThe epithelial cells of the small intestine contain bundles of microfilaments that are found in the microvilli found on the surface of the cell. Longer bundles of microfilaments form a band that extends around the circumference of epithelial cells. This band is attached to a cell junction that connects it to its neighbors.This band provides a great deal of structural support to the individual epithelial cells as well as the entirelayer of epithelial cells.Microfilaments also take part in:•Transport of materials inside cells•The shortening of a muscle cell during contraction•The separation of the daughter cells at the end of animal cell divisionMotor Proteins: Kinesin transports cargo toward the end of microtubules