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Transcript
Introduction to Cell Structure and Function Lecture By Dr. Dirk M. Lang Dept. of Human Biology Faculty of Health Sciences University of Cape Town South Africa Phone: ++27-21-406 6419 E-Mail: [email protected] 08/2007 Cellular Structures and Their Functions are Complex… I. Definition of a Cell: • Basic structural and functional units of life • The smallest units that display the characteristics of life, i.e. reproduction, metabolism, response to stimuli Prototypes of Cells: II. Cell Structure Detail III. General Subdivisions of a Cell A. Nucleus (regulatory center of the cell) C. Cytoplasm (everything between the plasma membrane and the nuclear compartment) B. Plasma Membrane (selectively permeable boundary between the cell and the environment) Organelles are individual compartments in the cytoplasm The Nucleus A. D. (Ribosome synthesis) C. (Chromosomes with DNA that regulate all cell activities) (Phospholipid bilayer with nuclear pores = membrane barrier to control what enters/leaves nucleus) B. (Proteins embedded in the nuclear envelope; most substances must pass through the pores to enter or leave the nucleus) The Plasma Membrane Structure: phospholipd bilayer with proteins embedded in and attached to the inner (intracellular) and outer (extracellular) surfaces The Plasma Membrane Most substances must use proteins to gain access to cell; proteins are selective Lipids move freely through bilayer Function: “selectively permeable” barrier; main responsibility is to ensure that the composition of extracellular fluid is not the same as the composition of the intracellular fluid The Plasma Membrane Serves as attachment site for the cytoskeleton Function (continued): phospholipids are liquid at body temperature so membrane functions as a “fluid mosaic” The Plasma Membrane (continued) Glycocalyx: protein and carbohydrate coat covering the extracellular surface of the plasma membrane • • Allows attachment to other cells Allows the cell to interact with the environment The Cytoplasm Cytoskeleton: network of protein fibers extending throughout the cytoplasm Flagellum Cytoplasm: water with dissolved salts, nutrients, enzymes; site of many chemical reactions Organelles: “little organs”found throughout cytoplasm Functions of the Cytoskeleton • Provides support and structure for the cell • Very dynamic, always remodelled • Important in cellular reproduction Functions of the Cytoskeleton (continued) Important in cell movement: • Cilia - short and numerous • Flagella - long, single (Moveable portions of the cytoskeleton that project from the surface of the cell) Organelles • Separate compartments within the cytoplasm formed by membranes • Each organelle has a specific function in the cell The Mitochondrion “Thread granule”; contained by double membrane Function of Mitochondrion Major source of cell’s energy: • Energy is taken from sugar, stored in molecule called ATP (adenosine triphosphate) • Requires oxygen to make this exchange (aerobic metabolism) The Ribosomes Sites of protein synthesis; function in the cytoplasm, but are assembled in the nucleolus Free: unbound Bound: attached to the endoplasmic reticulum; produce proteins for export and for the plasma membrane in the cytoplasm; produce proteins for use inside the cell The Cytomembrane System • System of tubes and chambers formed by membranes • Extensively distributed throughout the fluid cytoplasm • Involved in synthesis, modification, processing and packaging of cellular lipids and proteins 1. Endoplasmic Reticulum (ER) “within the cytoplasm network”, system of tubes and sacs formed by membranes Endoplasmic Reticulum (ER) a) Rough: with bound ribosomes • modifies proteins produced by the ribosomes b) Smooth: without bound ribosomes • doesn’t modify proteins • functions in lipid synthesis, drug detoxification, carbohydrate metabolism 2. The Golgi Apparatus A series of flattened sacs formed by membranes, functions in final lipid and protein processing prior to use by the cell The Golgi Apparatus • Proteins get shuttled from the ER to one end of the Golgi • In each sac, different modifications are made (proteins get individually tailored) • Proteins get sorted and shipped off to their destination (like the post office of the cell) 3. Vesicles Small membrane-bound structures that transport proteins and lipids around the cell • Little transporters that shuttle their contents from one organelle to another • When they contact the appropriate organelle, they fuse with its outer membrane and release their contents inside • Same for plasma membrane, allowing the export of materials from the cell (exocytosis) 4. The Lysosome Membrane-bound vesicle that contains digestive enzymes or toxic chemicals • Merges with vesicles containing food particles, invading bacteria • Harsh chemicals and enzymes degrade the food or bacteria, without harming rest of cell Interaction of ER and Golgi: Vesicle trafficking