Lesson 2 3 1 Plasma Membrane Extracellular Fluid Interstitial Fluid A watery medium that surrounds a cell Plasma membrane cell membrane separates cytoplasm from the extracellular fluid Cytoplasm region of cell found between the plasma membrane and nuclear membrane Cytosol liquid component found in the cytoplasm Intracellular structures collectively known as organelles 2015 Pearson Education Inc 3 1 Plasma Membrane Four 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 mem Chemical signals detected by plasma mem receptors 4 Structural Support stabilizes cells Anchors cells and tissues to each other or to extracellular matrix 2015 Pearson Education Inc 3 1 Plasma Membrane Plasma membrane composed of 1 Membrane Lipids largest component of plasma membrane Consists of Phospholipid bilayer two layers of phospholipids Hydrophilic heads toward watery environment both sides Hydrophobic fatty acid tails inside membrane Barrier to ions and water soluble compounds 2015 Pearson Education Inc Figure 2 18c Phospholipids and Glycolipids c In large numbers phospho lipids and glycolipids form micelles with the hydro philic heads facing the water molecules and the hydrophobic tails on the inside of each droplet Phospholipid Glycolipid Hydrophilic heads Hydrophobic tails WATER Note ions and H2O soluble compounds cannot move past the hydrophobic lipid tails Allows for interior of cell to have a different composition than the extracellular environment 3 1 Plasma Membrane 2 Membrane Proteins second largest component of plasma mem but 55 of the weight of the membrane Two general classes 1 Integral proteins Within the membrane If traverses the width of the membrane it is a transmembrane protein 2 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 2015 Pearson Education Inc 3 1 Plasma Membrane Function of Membrane Proteins 1 Anchoring proteins stabilizers Attach to inside cytoskeleton or outside extracellular protein fibers or other cells structures 2 Recognition proteins identifiers Label cells as normal or abnormal prevents immune system from attacking own cells Many recognition proteins are glycoproteins 3 Enzymes may be integral or peripheral proteins Catalyze reactions inside or outside of cell depending on location of enzyme 2015 Pearson Education Inc 3 1 Plasma Membrane Membrane Proteins 4 Receptor proteins change within the cell 5 Carrier proteins Bind and respond to ligands ions hormones to cause a Transport specific solutes through membrane May or may not require energy ATP Ex Glucose transporter does not require energy but Na and Ca2 transporters do 6 Channels integral protein with a central pore Regulate water flow and solutes through membrane Many channels are highly specific for a specific ion 2015 Pearson Education Inc 3 5 Diffusion and Osmosis Membrane Transport The plasma cell membrane is a barrier but Nutrients must get in Products and wastes must get out Permeability determines what moves in and 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 2015 Pearson Education Inc 3 5 Diffusion and Osmosis Membrane Transport Plasma membrane is selectively permeable Allows some materials to move freely Restricts other materials Selective permeability restricts materials based on Size Electrical charge Molecular shape Lipid solubility correlation between drug potency and lipid solubility ex Anesthetics such as chloroform ether 2015 Pearson Education Inc 3 5 Diffusion and Osmosis Membrane Transport Transport through a plasma membrane can be Active requiring energy ATP Passive no energy required Types of transport Diffusion passive Carrier mediated transport passive or active Vesicular transport active 2015 Pearson Education Inc ANIMATION Membrane Transport Diffusion 2015 Pearson Education Inc 3 5 Diffusion and Osmosis 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 Concentration gradient The difference between the solute at one area compared to another area creates a gradient potential energy 2015 Pearson Education Inc Figure 3 22 Overview of Membrane Transport Part 3 of 8 Diffusion Diffusion is the movement of molecules from an area of higher concentration to an area of lower concentration That is the movement occurs down a concentration gradient high to low Factors Affecting Rate Size of gradient molecular size electric charge lipid solubility temperature and the presence of membrane channel proteins Substances Involved Gases small inorganic ions and molecules lipid soluble materials Plasma membrane CO2 Example When the concentration of CO2 inside a cell is greater than outside the cell the CO2 diffuses out of the cell and into the extracellular fluid Extracellular fluid Figure 3 14 Diffusion 1 Placing a colored sugar cube into a water filled beaker establishes a steep concentration gradient 2 As the cube begins to dissolve many sugar and dye molecules are in one location and none are elsewhere 3 With time the sugar and dye molecules spread through the water 4 Eventually the concentration gradient is eliminated and the molecules are evenly distributed throughout the solution Note during diffusion of multiple substances treat the diffusion of each substance as if it was the only substance present 3 5 Diffusion and Osmosis 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 greater the difference the faster the diffusion 5 Electrical forces Opposites attract like charges repel 2015 Pearson Education Inc 3 5 Diffusion and Osmosis Diffusion across Plasma Membranes Can be simple or channel mediated Materials that diffuse through plasma membrane by simple diffusion include Lipid soluble compounds alcohols fatty acids and steroids Dissolved gases oxygen and carbon
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