ppt 35

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Information about ppt 35

Published on February 14, 2008

Author: Sigismondo



The Cell: The Cell Describe the typical cell. 2. Describe the structure of a cell membrane/plasma membrane. 3. Give the chemical composition of a cell membrane. 4. Explain the various ways by which substances pass across the cell membrane. The Cell: The Cell “building block of life” the typical cell: the typical cell The cell is the structural and functional unit of all living organisms, and is sometimes called the "building block of life; Some organisms, such as bacteria, are unicellular (consist of a single cell). Other organisms, such as humans, are multicellular. (Humans have an estimated 100 trillion or 1014 cells; the typical cell: the typical cell cell size is 10 µm; cell mass is 1 nanogram two major parts. † nucleus † cytoplasm. The nucleus is separated from the cytoplasm by the nuclear membrane. The cytoplasm, on the other hand, is separated from the surrounding fluids by the cell membrane. Slide 5: the typical cell 2 types of cell: Prokaryotes are not as structurally complex as eukaryotes, and were thought not to have any compartments enclosed by lipid membranes. In the past they were often viewed as having little internal organization, but slowly details are emerging about prokaryotic internal structures Eukaryotes are the most structurally complex known cell type, and by definition are in part organized by smaller interior compartments, that are themselves enclosed by lipid membranes that resemble the outermost cell membrane. Organelles : Organelles -discrete structure of a cell having specialized functions. -limited by a membrane Plasma membrane Ribosomes Rough ER Smooth ER Annulate Lamellae Mitochondria Golgi apparatus Coated Vesicles Lysosomes Peroxisomes Centrioles Slide 7: also called plasmalemma a thin, pliable, very elastic structure only 7.5 to 10 nm thick. semipermeable composed of a lipid bilayer & associated proteins Envelops the cell aids in maintaining its structural & functional integrity Sensory device recognize other cells & macromolecules Exhibits a trilaminar structure called The unit membrane The structure of a cell membrane/plasma membrane. Slide 8: the structure of a cell membrane ..\flash video\cellular membrane.swf It is mainly composed of a lipid bilayer of phospholipid molecules but with a large numbers of protein molecules protruding the layer. LIPID BILAYER is the basic structure of the cell membrane. It is composed entirely of phaopholipids and cholesterol. Interspersed in this lipid film are large globular protein molecules. Most of the membrane proteins are glycoproteins. the chemical composition of a cell membrane: the chemical composition of a cell membrane PROTEINS (55%) a.Integral Proteins b.Peripheral Proteins CARBOHYDRATES (3%) a.Proteoglycans b.Glycocaylx PHOSPOLIPIDS (25%) -consist of phosphate heads (hydrophilic) and two fatty acid tails (hydrophobic) CHOLESTEROL (13%) Other LIPIDS (4%) Glycolipids Slide 10: TRANSPORT SYSTEM [Described in a functional sense according to:] number of molecules moved direction of movement whether the movement is toward or away from the equilibrium 1. Uniport system – moves the molecule bidirectionally 2. Contransport sysyem - transfer of one solute depends upon the sequential transfer of another solute that can either be: a. Symport b. Antiport the various ways by which substances pass across the cell membrane Cross membrane transport of small molecules: 1. PASSIVE TRANSPORT (diffusion) a. Simple diffusion b. Facilitated diffusion 2. ACTIVE TRANSPORT Cross membrane transport of small molecules Cross membrane transport of large molecules ENDOCYTOSIS a. Pinocytosis b. Phagocytosis 2. EXOCYTOSIS the various ways by which substances pass across the cell membrane Slide 12: -random molecular movement of substance molecule by molecule, either through intermolecular spaces in the membrane or in combination with a carrier protein. a. Simple diffusion Factors: 1. Concentration gradient across the membrane 2. Electrical potential across the membrane 3. Permeability coefficient of the substance 4. Hydrostatic pressure gradient across the membrane 5. Temperature 6. Pressure of multitude of channels in membrane b. Facilitated diffusion Factors: 1. Concentration gradient across the membrane 2. Amount of carrier protein available 3. Rapidity of the solute-carrier interaction 4. rapidity of conformational charge for both loaded and unloaded carrier protein. 1. Passive transport (diffusion) 2. Active transport : 2. Active transport -molecules transported away from the thermodynamic equilibrium Ex. Sodium-Potassium Pump -the most important transport mechanism in the body which transport sodium out of cells to the exterior and at the same time pumps potassium ions from the outside to the inside. This is an example of Active Transport Process. Functions: 1. Maintain constant cel volume by decreasing the intracellular ion concentration and increasing the extracellular ion concentration, thus decreasaing the flow of water into cell. 2. Maintenance of a potential difference across the plasma membrane Slide 14: Common features of Facilitated diffusion & Active transport 1. Both involve carrier protein 2. Specify for ions, sugars & amino acids 3. Resemble substrate-enzyme reaction except that no covalent interactions occurs >specific binding site for solute >the carrier protein is saturable >there is binding constant for the solute & the whole system has a binding constant >structurally similar competitive inhibitor block transport Differences: 1. Facilitated diffusion operates bidirectionally Active transport is usually unidirectional 2. Active transport occurs against electrical on chemical gradient & so requires energy. Facilitated diffusion occurs down the electrochemical gradients & doesn’t require energy. presented by:: presented by: Vicheryl Lopez Qurrataini Balocang Medical BioChemistry JUNE182007

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