Cytoskeleton PDF Study Notes

Cytoskeleton V  ILOS The objectives of this lecture are –1) to understand the structure and function of Cytoskeleton. –2) to correlate their structures with basic functions.  Cytoskeleton It is complex network of protein structures. Providing struc...

Cytoskeleton V  ILOS The objectives of this lecture are –1) to understand the structure and function of Cytoskeleton. –2) to correlate their structures with basic functions.  Cytoskeleton It is complex network of protein structures. Providing structural support to the cell, the cytoskeleton also functions in cell motility and regulation  Cytoskeleton Types:  Cytoskeleton Types: – Actin {Microfilaments} – Intermediate {keratin} – Microtubules {Tubuline} Cilia, flagella & centrioles  Actin microfilament & microtubules are formed from globular proteins subunits. Intermediate filaments contains fibrous proteins subunites  Actin (Microfilaments) 7 nm in diameter A double twisted chain Actin subunit 7 nm Actin (Microfilaments) Individual subunits of actin microfilaments are known as globular actin (G-actin monomers). G-actin subunits assemble into long filamentous polymers called F-actin.  What does Atin do? Give mechanical support to cells. Structural role is to – bear tension, – &resist the pulling forces within the cell Allow cell mobility in cells which undergo amoeboid motion and phagocytosis (macrophage) Form scaffold on which myosin proteins generate force to support muscle contraction  Actin (Microfilaments) – Amoeboid movement interaction of actin filaments with myosin Cortex (outer cytoplasm): near the cell’s trailing gel with actin network end squeezes the Extending interior fluid forward pseudopodium into the pseudopodium Inner cytoplasm: sol with actin subunits What does cytoskeleton (Actin) do? – Regulation of physical state of the cytosol – maintaining the cell's shape – Participate in cell movement – Formation of contractile ring during cell division  Intermediate Filaments Diameter of 8-12nm, it is specialized for bearing tensions. Constructed of different molecular subunits keratin (protein) Keratin proteins Fibrous subunit (keratins coiled together)  INTERMEDIATE FILAMENTS Type Name Function I & II Acidic I & basic II Form complex network from nucleus to plasma Keratins membrane in epithelial cells III Desmin, Vimentin Support and structure IV Neurofialments Protect from mechanical stress and maintain structural integrity in various cell types V Nuclear lamina Structural role in the nucleus in all cells VI Nestin Implicated in nerve cell growth  MICROTUBULES Resemble hollow cylindrical tube. Composed of α and β tubulin (protein heterodimer ) Have a dynamic instability and continue to assemble and disassembel according to the need of the cell.  What does cytoskeleton (Microtubule) do? 1- Chromosomal movement during nuclear division (mitosis & meosis) During cell division, the microtubules form the mitotic spindle, and are responsible for pulling apart the chromatids. Fig.4.15  What does microtubules do? Function of microtubules 2- Intracellular transport – Allowing vesicle transport and other intracellular movements Fig.4.17  What does cytoskeleton (Microtubule) do? 3- Formation of cilia, flagella & centrosome Cilium & flagellum Cilium & flagellum 9+2 array system: – 9 doublets around 2 central singlet of MT. It arises from a centriole at the base of the system in cytoplasm [basal body]. Cilia & flagelum project from cell surface. The Centrosome and the Centrioles The Centrosome and the Centrioles Pair of centrioles Found near the nucleus. Give rise to spindle fibres {MT} Found in animal cells {none in plant cells} The Centrosome and the Centrioles