C HAPTER 9: T HE C YTOSKELETON A ND C ELL M OTILITY Overview of the Major Functions of the Cytoskeleton I. Cytoskeleton - composed of 3 well-defined filamentous structures that form an elaborate interactive network; has functions analogous to that of skeleton (support cell & play key role in mediating cell movements) A. Each of the 3 cytoskeletal filaments is a polymer of protein subunits connected to one another by weak, noncovalent bonds 1. Such construction lends itself to rapid assembly & disassembly, which is dependent upon complex cellular regulation 2. Each cytoskeletal element has distinct mechanical properties B. The 3 types of cytoskeletal elements 1. Microtubules (MTs) - hollow, rigid cylindrical tubes with walls composed of tubulin subunits 2. Microfilaments (MFs) - solid, thinner structures composed of actin 3. Intermediate filaments (IFs) - tough, ropelike fibers composed of a variety of related proteins II. Function in number of interrelated activities – they are highly dynamic; can do rapid & dramatic reorganization; often require accessory proteins that are not part of filaments A. Dynamic scaffold; provides structural support that helps determine cell shape (ex.: RBC spectrin-1. The flat, rounded shape of many cultured cells depends on a radial array of MTs in cell cytoplasm B. Internal framework that is responsible for positioning organelles in cell interior (ex.: polarized epithelial cells - organelles arranged in defined pattern along an axis from the apical to the basal end of the cell) C. 2. Movement of membranous carriers from ER to Golgi complex 3. Transport of vesicles containing neurotransmitters down the length of the nerve cell; carry vesicles from synthesis site to axon terminal. D. Force-generating apparatus - move cells from place to place (cilia, flagella, pseudopodia) 1. Single-celled organisms - crawl over surface of solid substratum or propel themselves through aqueous environment with aid of specialized locomotor organelles (cilia from cell surface) 2. Multicellular animals have variety of cells capable of independent locomotion - sperm, white blood cells, fibroblasts, highly motile tip of growing axon (its movement resembles crawling blood cell) F. Separation of chromosomes during mitosis & meiosis & cytokinesis (splitting parent cell into two daughter cells); essential component of cell's division machinery The Study of the Cytoskeleton II. The use of live-cell fluorescence imaging – traditional light microscopy is tool used to learn about cell A. New technique allows us to view things below resolution limit of regular light scopes (too small); used to study dynamics of cytoskeleton in live cells – fluorescence microscope; known as live-cell imaging
This is the end of the preview. Sign up to
access the rest of the document.