Cytoskeleton & Cell Inclusions PDF

 Cytoskeleton & Cell inclusions 1- Cytoskeleton: Types, structure & functions. 2- Centrosome: Structure & function. 3- Cell inclusions: Types.  Cytoskeleton The cytoskeleton is a network of structural proteins(non-membranous cell organelles). ...

 Cytoskeleton & Cell inclusions 1- Cytoskeleton: Types, structure & functions. 2- Centrosome: Structure & function. 3- Cell inclusions: Types.  Cytoskeleton The cytoskeleton is a network of structural proteins(non-membranous cell organelles).  Types of cytoskeleton 3 types, depending on their thickness& their structural proteins: 1- Microfilaments. 2- Microtubules. 3- Intermediate filaments.  1-Microfilaments (actin filaments) Diameter: 7 nm. LM: can be visualized by using immunohistochemical staining.  1-Microfilaments (actin filaments) EM: thin electron dense filaments. Structural proteins: monomers of G-actin (globular actin) polymerize to form F-actin (filamentous actin) arranged as a double helix. They are dynamic structures that can elongate and shorten  Functions of microfilaments A- Cell motility for: Cell migration. Cytoplasmic streaming: during movement of organelles and transport of vesicles. Cytokinesis:formation of contractile ring during cell division. Muscle contraction associated with myosin. B-Structural role: Maintenance of the cell shape. Formation the core of microvilli.  2-Microtubules Diameter: 25 nm. LM picture: by using immunohistochemical staining. EM picture: fine tubules. Structural proteins: A- a globular protein dimer called tubulin (each is composed of alpha and beta subunits). B- Chains of tubulin dimers form a protofilament. C- The wall of a microtubule is made up of 13 protofilaments that run longitudinally.  Motor proteins associated with microtubules Kinesin and dynein; they use ATP to provide energy for movement of vesicles and organelles along the microtubules.  Microtubules are dynamic structures; can elongate and shorten  Functions of microtubules 1- Transport: of organelles and vesicles in the cytoplasm. 2- Structural role: Formation of the mitotic spindle. Formation of centrioles, cilia & flagella.  The microtubule organizing centers 1- Centriole which forms the mitotic spindle. 2- The basal bodies of cilia and flagella.  3- Intermediate filaments Diameter:10 nm LM : by using immunohistochemical staining. EM : electron dense filaments thicker than actin filaments. Structural proteins: like woven ropes.  Function of intermediate filaments They are the most stable (not dynamic) types of the cytoskeletal thus they play a structural role.  Classification of intermediate filaments According to their protein composition and their cellular distribution into: A- Cytoplasmic: 1- Keratin: epithelial cells. 2- Vimentin: in the cells of mesenchymal origin e.g. fibroblasts. 3- Desmin: muscle cells. 4- Glial fibrillary acidic protein: neuroglia. 5- Neurofilaments: nerve cells. B- Nuclear: Lamins: lining the inner nuclear envelope.  Intermediate filaments The intermediate filaments (except for the lamins) are located in specific tissue types; they can be used to determine the origin of cancer by immunohistochemical staining. Cytoskeleton Microfilaments Microtubules Intermediate filaments 1- diameter 7 nm. 25 nm. 10 nm. 2- LM Seen only by immunohistochemistry. Seen only by Seen only by immunohistochemistry immunohistochemistry 3- EM Thin electron dense filaments. Fine tubules. Thicker electron dense filaments. 4- Structural Monomers of G actin polymerize to form F Tubulin dimer polymerize to Woven ropes. proteins actin. protofilaments. 13 protofilaments form a microtubule, 5- Functions Dynamic Dynamic. Not dynamic. 1- Muscle contraction. 1- Transport of organelles & Structural support. 2- Contractile ring in cell division. vesicles. 3- Pseudopodia in migration. 2- Formation of centrioles, cilia 4- Microvilli. & flagella. 5- Cytoplasmic streaming. Centrosomes  Centrosome Definition: a non-membranous organelle. EM: 1- It is formed of 2 centrioles, perpendicular to each other. 2- Each centriole is composed of 9 triplets of microtubules (a sum of 27 microtubules). 3- Each triplet is composed of three microtubules (one complete; formed of 13 protofilaments and 2 incomplete;each is formed of 10 protofilaments).  Functions of centrosome 1- It is the microtubule- organizing center. 2- Formation of mitotic spindles. 3- Formation of cilia and flagella. Cytoplasmic inclusions 1- Stored food  A-Glycogen Storage form of carbohydrates. Function: source of energy. Sites: mainly in liver and muscle cells. LM: H&E: not visualized as they dissolve during preparation of the specimen leaving a pale vacuolated cytoplasm. Periodic-acid Schiff: appears magenta red. Best's carmine:appears bright red. EM: dense granules, larger than ribosomes. In cytoplasm of hepatocytes, glycogen appears as rosette-shaped aggregates  B-Lipids Function: 1- Source of energy. 2- Synthesis of membranes and steroid hormones. Sites: stored in the adipocytes; many other cell types contain few small lipid droplets. LM: H&E: not visualized because they dissolve during preparation of the specimen leaving a pale vacuolated cytoplasm. Osmium tetroxide: appear black. EM: grey non- membrane bounded small droplets or large globules.  C-Proteins Site: in protein- synthesizing cells e.g. salivary gland and pancreas. LM: eosinophilic zymogen granules. EM: homogenous electron dense membrane-bounded secretory granules. 2- Pigments  A-Endogenous pigments 1- Hemoglobin: in red blood cells. 2- Hemosiderin: brownish granules in phagocytic cells of liver and spleen following phagocytosis of old RBCs. 3- Melanin pigment: brown to black granules. 4- Lipofuscin pigment: yellow-brown pigment present in cells with long life span.  B- Exogenous pigments 1- Tattooing: colored pigments are injected into the deep layers of the skin. 2- Dust and smokes: in lung of smokers and people living in polluted areas. Which statement is the best to describe the intermediate filaments? 1- They are dynamic structure that maintain the cell shape. 2- They are responsible for movement of organelles and vesicles. 3- They are permanent structures that resist tension exerted on the cell. 4- They form the core of microvilli. Which statement is the best to describe the intermediate filaments? 1- They are dynamic structure that maintain the cell shape. 2- They are responsible for movement of organelles and vesicles. 3- They are permanent structures that resist tension exerted on the cell. 4- They form the core of microvilli.