Delphinidin

The cytoskeleton is involved in movement within a cell and in a cell’s architecture. It is an intricate network constructed mainly of two kinds of fibers—microtubules and microfilaments. Microtubules control the addition of cellulose to the cell wall. They are also involved in cell division, movement of cytoplasmic organelles, controlling the movement of vesicles containing cell-wall components assembled by dictyosomes, and movement of the tiny whiplike flagella and cilia possessed by some cells.

Microtubules are unbranched, thin, hollow, tubelike structures that resemble tiny straws. They are composed of proteins called tubulins and are of varying lengths, most being between 15 and 25 nanometers in diameter. They are most commonly found just inside the plasma membrane. Microtubules are also found in the special fibers that form the spindles and phragmoplasts of dividing cells.

Microfilaments, which play a major role in the contraction and movement of cells in multicellular animals, are present in nearly all cells. They are three or four times thinner than microtubules and consist of long, fine threads of protein with an average diameter of 6 nanometers. They are often in bundles and appear to play a role in the cytoplasmic streaming (sometimes referred to as cyclosis) that occurs in all living cells. When cytoplasmic streaming is occurring, a microscope reveals the apparent movement of organelles as a current within the cytoplasm carries them around within the walls. This streaming probably facilitates exchanges of materials within the cell and plays a role in the movement of substances from cell to cell. The precise nature and origin of cytoplasmic streaming is still not known, but there is evidence that bundles of microfilaments may be responsible for it. Other evidence suggests that it may be related to the transport of cellular substances by microtubules.