Lecture 7: Cytoskeleton PDF

Associate professor Zanda Daneberga Cell division - cytoskeleton 1 ◼ The cytoskeleton of a cell consists of three filamentous structures: microtubules, microfilaments = actin filaments, intermediate filaments....

Associate professor Zanda Daneberga Cell division - cytoskeleton 1 ◼ The cytoskeleton of a cell consists of three filamentous structures: microtubules, microfilaments = actin filaments, intermediate filaments. 2 Cytoskeleton - functions ◼ Maintains cell`s shape. Change shape during movement (e.g. cell division; organelle migration; cell migration); ◼ Positions organelles; ◼ Resists deformation; ◼ Transports intracellular cargo (e.g. vesicles), assists in the transportation of communication signals between cells. 3  Microtubules ◼ The largest type of filament, composed of a protein tubulin, diameter ~25 nanometers (nm). ◼ Tubulin is composed of α – tubulin and β -tubulin subunits assembled into linear protofilaments. ◼ Microtubules are structures that can rapidly grow (via polymerization) Eukaryotic cells stained with tubuline or shrink (via depolymerization) in antibodies, 40x resolution. size, depending on how many tubulin molecules they contain. Source: RSU Institute of Oncology, researcher Valdis Pirsko 4  Microtubules ◼ A single microtubule contains 10 to 15 protofilaments (13 in mammalian cells) that wind together to form a 24 nm wide hollow cylinder. 5 Centrosome ◼ In cells, the minus ends of microtubules are anchored in structures called microtubule organizing centers (MTOCs). The primary MTOC in a cell is called the centrosome. ◼ The centrosome consists of two centrioles. ◼ Duplicated during S phase of the cell cycle. Source: Stearns T, Cell, 2001 105417-420DOI: (10.1016/S0092-8674(01)00366-X) 6  Centrioles ◼ Occur as paired cylindrical organelles together with pericentriolar material (PCM - containing more than 100 different proteins). ◼ Constructed of microtubules. ◼ Organise the PCM to produce microtubules including mitotic spindle fibres. 7 Intermediate filaments ◼ Composed from different protein (~70 in humans) subunits, diameter ~10 nm. Identified only in animal cells. ◼ Intermediate filaments associated with specific cell types – neurofilaments in neurons; desmin filaments – muscule cells; keratins - epithelial cells. 8 Microfilaments ◼ The smallest type of filament, composed of the contractile protein actin, diameter ~8 nm. ◼ Microfilaments are particularly prevalent in muscle cells. 9  Motor proteins ◼ Use energy derived from ATP hydrolysis to generate movement and force. ◼ Motor proteins involved in cell movement: Kinesin - move along microtubules to pull organelles toward the cell membrane. Dynein - used to pull cellular components inward, toward the nucleus, work to slide microtubules. Myosin - interact with actin to perform muscle contractions, involved in cytokinesis, endocytosis, and exocytosis. 10