1. Microtubules:
* Structure: Microtubules are hollow cylinders made up of the protein tubulin. They are the largest filaments in the cytoskeleton, with a diameter of about 25 nanometers.
* Function:
* Structural support: Microtubules provide rigidity and shape to cells.
* Cell division: Microtubules form the spindle fibers that separate chromosomes during cell division.
* Organelle movement: Microtubules serve as tracks for motor proteins like kinesin and dynein, which transport organelles and vesicles within the cell.
* Cilia and flagella: Microtubules form the core of cilia and flagella, which are hair-like structures involved in movement.
* Examples: Microtubules are found in all eukaryotic cells, including animal, plant, and fungal cells.
2. Microfilaments:
* Structure: Microfilaments are thin, solid rods made up of the protein actin. They are the smallest filaments in the cytoskeleton, with a diameter of about 7 nanometers.
* Function:
* Cell shape and movement: Microfilaments are responsible for the shape and movement of cells, particularly in muscle cells.
* Cytoplasmic streaming: Microfilaments contribute to the movement of cytoplasm within the cell.
* Endocytosis and exocytosis: Microfilaments help in the formation of vesicles for endocytosis and exocytosis.
* Cell division: Microfilaments form a contractile ring during cytokinesis, which divides the cell into two daughter cells.
* Examples: Microfilaments are found in all eukaryotic cells, but they are especially prominent in muscle cells and cells involved in movement.
In addition to these two main structures, the cytoskeleton also contains intermediate filaments, which provide mechanical support and help to anchor cells together.
