Cell Structure & Cell Division

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2. SYNOPSIS ..STRUCTURE OF MAMMALIAN CELL: THE CELL IN BRIEF MEMBRANE STRUCTURE THE NUCLEUS THE NUCLEOLUS NUCLEAR ENVELOPE RIBOSOMES ENDOPLASMIC RETICULUM GOLGI APPARATUS 3. LYSOSOMES PEROXISOMES MITOCHONDRIA CYTOSKELETON MICROFILAMENTS INTERMEDIATE FILAMENTS MICROTUBULES CENTROSOME 4. The cell is the functional unit of all livingorganism. Human cell consist ofNucleus Cytoplasmlargest organelle contains a number oforganelles each with adefined function 5. THE CELL IN BRIEF All cells are bounded by an external lipidmembrane, called the plasma membrane orplasmalemma PM, which serves as a dynamicinterface with the external environment. Functions : transfer of nutrients and metabolites, attachment of the cell to adjacent cells and extracellular matrix, and communication with the external environment 6. NUCLEUS - largest organelle and itsnucleoplasm is bounded by nuclearmembrane. contains the genetic material of the cell. CYTOPLASM - contains a variety of otherorganelles, most of which are also bounded bymembranes. ENDOPLASMIC RETICULUM - extensivesystemofflattened membrane-boundtubules, saccules and flattened cisterns.Widely distributed throughout the cytoplasm. 7. GOLGI APPARATUS - discrete system ofmembrane-bound saccules, typically locatedclose to the nucleus. MITOCHONDRIA - Scattered free in thecytoplasm are a number of relativelylarge, elongated organelles having smooth outermembrane and a convoluted inner membranesystem. 8. In addition to these major organelles, the cellcontains a variety of other membrane-boundstructures, including intracellular transportvesicles and a lysosome . The cytoplasmic organelles are suspended incytosol. Within the cytosol, there is a network of minutetubules and filaments, collectively known as thecytoskeleton, which provides structuralsupport for the cell and its organelles, as well asproviding a mechanism for transfer of materialswithin the cell and movement of the cell itself 9. MEMBRANE STRUCTURE SingerandNicholson,in the early1970s, proposed the fluid mosaic model ofmembrane structure which is now generallyaccepted. Cell membranes consist of a bilayer ofphospholipid molecules that are amphipathic 10. Polar, hydrophilic (water-loving) head:Derived from glycerol conjugated to a nitrogenous compound (positive charge) via a phosphate bridge (negative charge) Non-polar, hydrophobic (water-hating) tail:Two long-chain fatty acids, each covalently linked to the glycerol component of the polar head. One of the fatty acids is a straight-chain saturated fatty acid, while the other is an unsaturated fatty acid which is kinked at the position of the unsaturated bond. 11. The weak intermolecular forces that hold thebilayer together allow individual phospholipidmolecules to move relatively freely within eachlayer. The fluidity and flexibility of the membrane isincreased by the presence of unsaturated fattyacids bridge. Cholesterol molecules are also present in thebilayer in an almost 1:1 ratio with phospholipids 12. Protein molecules make up almost half of thetotal mass of the membrane. intrinsic or integral extrinsic or peripheral proteinsproteinstransmembrane proteinsSpan entire length/thickness of membrane to be exposed to each surface. 13. Transmembrane proteins have a variety offunctions including cell-cell adhesion, cell matrix adhesion, communication and formation of pores or channels for the transport of materials into and out of the cell. 14. On the external surface of the plasma membranepolysaccharide layer termed glycocalyx,involved in:Cell recognition phenomena,Formationofintercellular adhesions,Adsorption of molecules to the cell surfaceIn some situations, provides mechanical andchemical protection for the plasma membrane 15. The electron micrograph - high magnification view of the plasma membrane PMof the minute surface projections (microvilli) MV of a lining cell from thesmall intestine 16. NUCLEUS Largest organelle in the cell. Control centre of the cell, blueprint from whichall the other components of the cell areconstructed. This blueprint is stored in the form ofdeoxyribonucleic acid (DNA) arranged inthe form of chromosomes 17. The nucleus containsa) DNA (