Lesson 2 Material 3 1 Plasma Membrane 12 08 2015 Extracellular Fluid Interstitial Fluid o A watery medium that surrounds a cell o Plasma Membrane cell membrane separates cytoplasm o Cytoplasm from extracellular fluid membrane and nuclear membrane region of cell found between the plasma Cytosol liquid component found in cytoplasm Intracellular structures collectively known as organelles 4 general functions of the plasma membrane 1 Physical Isolation Barrier separates inside from outside of cell 2 Regulation of Exchange with the Environment Ions and nutrients enter Wastes eliminated and cellular products released 3 Sensitivity to the Environment Extracellular fluid composition can alter plasma Chemical signals detected by plasma membrane membrane receptors 4 Structural Support Anchors cells and tissues to each other or to extracellular matrix Stabilizes cells Plasma membrane composed of 1 Membrane lipids Largest component of plasma membrane Consists of Phospholipid bilayer two layers of phospholipids Hydrophilic heads towards watery environment on both sides Hydrophobic fatty acid tails inside membrane Barrier to ions and water soluble compounds allows for interior of cell to have a different composition than extracellular enviornment 2 Membrane proteins Second largest component of plasma membrane but 55 of the weight of membrane Two general classes Integral proteins Within the membrane If traverses the width of the membrane it is a transmembrane protein Peripheral proteins Bound to inner or outer surface of the membrane Less numerous than integral proteins NOTE membrane proteins may be located at specific locations on a cell inside layer or outside layer of plasma membrane Functions of Membrane Proteins Anchoring proteins stabilizers Attach to inside cytoskeleton or outside extracellular protein fibers or other cells structures Recognition proteins identifiers Label cells as normal or abnormal prevents immune system from attacking own cells Many recognition proteins are glycoproteins Enzymes may be integral or peripheral proteins Catalyze reactions inside or outside of cell depending on location of enzyme Receptor proteins Bind and respond to ligands ions hormones to cause a change within the cell Carrier proteins Transport specific solutes through membrane May or may not require energy ATP o EX glucose transporter does NOT require energy but Na and Ca2 transporters do Channels integral protein with a central pore Regulate water flow and solutes through Many channels are highly specific for a membrane specific ion 3 5 Diffusion and Osmosis Membrane Transport o The plasma cell membrane is a barrier but Nutrients must get in Products and wastes must get out o Permeability determines what moves in or out of a cell and a membrane that Lets nothing in or out is impermeable Lets anything pass is freely permeable Restricts movement is selectively permeable o Transport through a plasma membrane can be Active requiring energy via ATP Passive no energy required o Types of transport Diffusion passive Carrier mediated transport passive or active Vesicular transport active o Diffusion All molecules are constantly in motion Molecules in solution move randomly Random motion causes mixing Concentration is the amount of solute dissolved substance in a solvent liquid component EX in drop in a glass of water ink diffuses NOTE during diffusion of multiple substances treat the diffusion of each substance as if it was the ONLY substance present Concentration gradient The difference between the solute at one area compared to another area creates a gradient potential energy Factors influencing diffusion 1 Distance the particle has to move 2 Molecule size Smaller is faster 3 Temperature More heat faster motion 4 Concentration gradient The difference between high and low concentrations the greater the difference the faster the diffusion 5 Electrical forces Opposites attract like charges repel Diffusion across plasma membranes Can be simple or channel mediated Materials that diffuse through plasma membrane by simple diffusion include o Lipid soluble compounds alcohols fatty acids steroids o Dissolved gases oxygen and carbon dioxide Channel mediated diffusion uses a channel to transport o Water soluble compounds and ions o Factors in channel mediated diffusion Size Charge Interaction with the channel leak channels NOTE passive channels are always open and will allow for movement of ions in either direction The net flow of these ions is from an area of higher concentration to an area of lower concentration down its concentration gradient o Osmosis A special case of diffusion Osmosis is the diffusion of water across the cell membrane Factors that affect osmosis More solute molecules lower concentration of water molecules Membrane must be freely permeable to water selectively permeable to solutes Water molecules diffuse across membrane toward solution with more solutes Volume increases on the side with more solutes Water moves to that side and dilutes that side to make it closer in solute concentration as the other side NOTE applied force to counter the increase in H2O volume osmotic pressure on the opposite side is called the hydrostatic pressure Osmolarity and Tonicity o The osmotic effect of a solute on a cell Two fluids may have equal osmolarity total solute concentration but different tonicity effect of the osmotic solution on the cells o Isotonic iso same tonos tension A solution that does not cause osmotic flow of water in or out of a cell o Hypotonic hypo below Has less solutes and loses water through osmosis o Hypertonic hyper above Has more solutes and gains water by osmosis o A cell in a hypotonic solution Gains water Ruptures hemolysis of red blood cells if left unchecked o A cell in a hypertonic solution Loses water Shrinks crenation of red blood cells o NOTE a person suffering from severe blood loss is treated with a 0 9 solution of NaCl that is isotonic to body cells An alternative treatment includes the addition of dextran cannot cross membranes to increase blood volume and pressure by causing osmosis of H20 from tissue into blood 3 6 Carriers and Vesicles Carrier Mediated Transport moves ions and organic substrates o Characteristics include Specificity one transport protein one set of substrates Saturation limits rate depends on transport proteins not substrate Regulation cofactors such as hormones o Carrier mediated transport can involve Cotransport also known as symport Two substances move
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