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3A  Membrane: a thin covering that forms the outer boundary of the cell › Membranes sense and respond the changes in the surrounding environment.

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Presentation on theme: "3A  Membrane: a thin covering that forms the outer boundary of the cell › Membranes sense and respond the changes in the surrounding environment."— Presentation transcript:

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3  Membrane: a thin covering that forms the outer boundary of the cell › Membranes sense and respond the changes in the surrounding environment

4  Composed of molecules of lipids (phospholipids and cholesterol) and proteins.  The proteins perform the activities in the membrane  Fluid mosaic model: the lipid molecules form a flexible two-layered film in which proteins are embedded

5  Lipid Bi-layer: phospholipids organized in two layers › The phospholipids are in a shape like a head and a tail  Hydrophobic  Hydrophobic tails inside  Hydrophilic  Hydrophilic heads outside

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7  Membrane is Fluid  Lipids have rapid lateral movement  Fluidity depends on lipid composition

8 Unsaturated Saturaded  All C-C bonds are single bonds  Straight chain allows maximum interaction of fatty acid tails  Make membrane less fliuid  Solid at room temperature  Some C=C bond (double bonds)  Bent chain keeping tails apart  Make membrane more fluid  Liquid at room temperature

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10  Selective Permeability means that the plasma membrane allows some substances to cross through it while also keeping other substances out.

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12  Diffusion is the passive movement of particles (atoms, ions or molecules) from a region in which they are in higher concentration to regions of lower concentration.  It continues until the concentration of substances is uniform throughout.  High temperatures increase diffusion; large molecules slow diffusion

13  Facilitated diffusion is a type of passive transport that allows substances to cross membranes with the assistance of special transport proteins. › Channel proteins › Carrier proteins

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