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An elaborate network of filamentous proteinaceous structures consisting of following types of fibres present in the cytoplasm is collectively referred to as the cytoskeleton:

Microtubules

Microtubules are the largest of the fibers of the cytoskeleton at approximately 23 nm. They are hollow tubes made up of alpha and beta tubulin. Microtubules form flagella-like structures, which are the "tails" that propel a cell forward. They are also found in structures such as cilia, which are appendages that increase the surface area of a cell and in some cases allow the cell to move. Most of the microtubules in an animal cell come from a cell organelle called the centrosome, which is a microtubule organizing center (MTOC). The centrosome is found near the middle of the cell, and microtubules exit from it. Microtubules are important in forming the spindle apparatus (or mitotic spindle), which separates sister chromatids so that one copy can go to each daughter cell during cell division. They are also involved in the transport of molecules within the cell and in the formation of cell walls in plant cells.

Microfilaments

Microfilaments are also called actin filaments because they are mostly composed of the protein actin. Their structure is two strands of actin wound in a spiral. They are about 7 nanometers thick, making them the thinnest filaments in the cytoskeleton. Microfilaments have many functions. They aid in cytokinesis, which is the division of a cell's cytoplasm when it divides into two daughter cells. They aid in cell motility and allow single-celled organisms such as amoebas to move. They are also involved in cytoplasmic streaming, which is the flow of the cytosol throughout the cell. Cytoplasmic streaming transports nutrients and cell organelles. Microfilaments are also part of muscle cells and allow these cells to contract with myosin. Actin and myosin are the two main components of muscle contraction.

Intermediate filaments

They are about 8–12 nm wide. They are called intermediate because they are in between the size of microfilaments and microtubules. Intermediate fibers are composed of various proteins such as keratin (found in hair and nails, and also in animals with scales, horns or hoofs), vimentin, desmin, and lamin. All intermediate fibers are found in the cytoplasm, except for vitamin K, which is found in the nucleus and helps support the nuclear envelope that surrounds the nucleus. Intermediate fibers in the cytoplasm maintain the shape of the cell, tolerate stress and provide structural support to the cell.