Cytoskeleton Introduction to Cytoskeleton: Microtubules: have a diameter of about 25 nm (involved in mitotic spindle, cilia, and flagella) and help with transport of substances within the cell Intermediate Filaments: have a diameter of about 10 nm and provide structural support to the cell (do this by helping mechanical stress) Microfilaments: have a diameter of about 7 nm and help with movement from within (microfilaments help change the shape of the cell during different processes) Microfilaments & Intermediate Filaments: Microfilaments: made up of the protein actin and are mainly involved in the gross movement of the cell (2 actin polymers wrapped around each other) Intermediate Filaments: made up of different types of proteins that twist up to form their structure (are permanent, meaning once they are made it doesn’t change as much as the other cytoskeletal types) and resist mechanical stress Microtubules: Microtubules: made up of two proteins (alpha tubulin and beta tubulin that come together to form a dimer) where the dimers are put together in order the walls of the tubules (are anchored to microtubule organizing centers) Can be elongated or shortened based on the needs of the cell 2 Types of microtubule organizing centers: 1. Centrosome: made up of two centrioles at right angles to each other and each centriole is made up of 9 triplets of microtubules (one per cell and duplicate during mitosis - S phase) and function as origin point for microtubules 2. Basal Body: microtubule organizing center in cells that have cilia or flagella Centromere: center of the chromosome and is attached to the kinetochore which attaches to the mitotic spindle “9 plus 2” Arrangement: is how the microtubules are arranged in a cross section of the flagella In neurons, kinesin and dynein help transport substances across an axon (like vesicles, proteins, lipids, and even organelles) known as axonal transport