Chapter 7 Notes

Chapter 7 Notes - Chapter 7 Membrane Structure and Function Life at the edge Plasma membranes are the boundary that separates the living cell from

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Chapter 7 Membrane Structure and Function Life at the edge Plasma membranes are the boundary that separates the living cell from its surroundings Selective permeability- allows some substances to cross it more easily than others. o Permitting the uptake of nutrients and elimination of waste products o The ability of the cell to discriminate in its chemical exchanges with environment Cellular membrane Are composed of lipids and proteins o Lipids in most membranes are phospholipids Amphipathic molecule- a phospholipids that have both a hydrophilic regions and a hydrophobic region. Fluid mosaic model- the membrane is a fluid structure with a mosaic of various proteins embedded in or attached to a double layer of phospholipids. Membranes were first seen in 1950 with an electron microscope. Sandwich model- a phospholipids bilayer between two layers of protein. o Problem was the protein placement o Membrane proteins are not soluble in water Freeze fracture- splits the membrane along the middle of the phospholipid bilayer. Fluidity of membranes A membrane is held together primarily by hydrophobic interactions o Which are weaker than covalent bonds The lateral movement of phospholipids within the membrane is rapid Some membrane proteins seem to move in a highly directed manner o Driven along cytoskeletal fibers by motor proteins connected to the membrane proteins cytoplasmic regions. A membrane remains fluid as temperature decreases until finally the phospholipids settle into a closely packed arrangement and the membranes solidifies o Depends on the type of lipids the membrane is made of Steroid cholesterol are wedged between phospholipid molecules in the plasma membranes of animal cells, has different effects on membrane fluidity at different temperatures. o Cholesterol makes the membrane less fluid by restraining phospholipid movement o Also hinders the close packing of phospholipids, it lowers the temp required for the membrane to solidify. “Temperature buffer.” o Membrane solidifies, its permeability changes, and enzymatic proteins in the membrane may become inactive. Membrane Proteins A membrane is a collage of different proteins embedded in the fluid matrix of the lipid bilayer.
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More than 50 kinds of proteins have been found so far in the plasma membrane in human red blood cells. Phospholipids from the main fabric of the membrane, but proteins determine most of the
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This note was uploaded on 04/26/2009 for the course BIOL 111 taught by Professor Rizzo during the Spring '07 term at Texas A&M.

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Chapter 7 Notes - Chapter 7 Membrane Structure and Function Life at the edge Plasma membranes are the boundary that separates the living cell from

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