Plasma Membrane & Transport

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  • Created by: _Sarah
  • Created on: 10-10-13 16:46

Plasma Membrane

  • All cells are surrounded by a plasma membrane (cell surface membrane) 
  • Light microscope-single line, Electron microscope-double line
  • Distance across cell membrane - 7/8nm
  • 'Fluid mosaic' model - components free to move, proteins look mosaic
  • Bi-layer of phospholipid
  • Consists of protein and phospholipid
  • Hydrophilic heads, Hydrophobic tails
  • Intrinsic Protein-extend across both layers
  • Extrinsic Protein-occur on the surface or partly embedded
  • Proteins provide support, allow active transport by forming ion channels, form recognition sites, act as carriers transporting water-soluble substances across the membrane
  • Facilitated diffusion-diffusion involving the presence of protein carrier molecules to allow the passive movement of substances across plasma membranes
  • Lipid soluble molecules can pass through
  • Ions or larger molecules are insoluble in lipids and so require help
  • Channel proteins-help ions move through
  • Carrier proteins-carry larger molecules through
  • A solute may be taken across a cell membrane by a special carrier molecule

Major Functions:

  • Taking up nutrients
  • Secreting chemicals
  • Cell recognition
  • Water is ionic
  • Water will never pass easily through the bi-layer as its ionic and so requires intrinsic proteins
  • Factors Affecting the Permeability of a Plasma Membrane-Heat & Organic solvent


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