Biology 11 Human Biology, TTh 8;00-9:20 Dr. Telleen Lecture 5 Cell Membrane Transport

Biology 11 Human Biology, TTh 8;00-9:20 Dr. Telleen Overcoming the Cell Barrier  The 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  A membrane is:  Impermeable if it lets nothing in or out  Freely permeable if it lets anything pass  Selectively permeable if it restricts movement  Cell membranes are selectively permeable:  Allow some materials to move freely  Restrict other materials Membrane Transport: Fat- and Water-Soluble Molecules PLAY

Biology 11 Human Biology, TTh 8;00-9:20 Dr. Telleen Restricted Materials  Selective permeability restricts materials based on:  Size  Electrical charge  Molecular shape  Lipid solubility

Biology 11 Human Biology, TTh 8;00-9:20 Dr. Telleen Diffusion in Solutions  All molecules are constantly in motion  Molecules in solution move randomly  Random motion causes mixing  Concentration is the amount of solute in a solvent  Concentration gradient:  More solute in one part of a solvent than another  Solutes move down a concentration gradient:  Molecules mix randomly  Solute spreads through solvent  Eliminates concentration gradient Membrane Transport: Diffusion PLAY

Biology 11 Human Biology, TTh 8;00-9:20 Dr. Telleen Factors Affecting Diffusion Rates  Distance the particle has to move  Molecule size:  Smaller is faster  Temperature:  More heat, faster motion  Gradient size:  The difference between high and low concentration  Electrical forces:  Opposites attract, like charges repel

Biology 11 Human Biology, TTh 8;00-9:20 Dr. Telleen Osmosis  Osmosis is the movement of water across the cell membrane Osmotic Pressure is the force of a concentration gradient of water Equals the force (hydrostatic pressure) needed to block osmosis

Biology 11 Human Biology, TTh 8;00-9:20 Dr. Telleen Diffusion vs. Osmosis

Biology 11 Human Biology, TTh 8;00-9:20 Dr. Telleen Effects of Osmosis on Cells  Isotonic – solutions with the same solute concentration as that of the cytosol  Hypertonic – solutions having greater solute concentration than that of the cytosol; water leaves the cell causing crenation (shrinkage)  Hypotonic – solutions having lesser solute concentration than that of the cytosol; water enters the cell causing swelling and potential lysis Tonicity – how a solution’s osmolarity affects cell volume

Biology 11 Human Biology, TTh 8;00-9:20 Dr. Telleen Hydrostatic and Osmotic Pressure  Hydrostatic pressure = water pressure  Filtration is the passage of water and solutes through a membrane by hydrostatic pressure  Pressure gradient pushes solute-containing fluid from a higher-pressure area to a lower-pressure area  Osmotic pressure can create an important counter force against hydrostatic pressure

Biology 11 Human Biology, TTh 8;00-9:20 Dr. Telleen KEY CONCEPT  Concentration gradients tend to even out  In the absence of a membrane, diffusion eliminates concentration gradients  When different solute concentrations exist on either side of a selectively permeable membrane, osmosis moves water through the membrane to equalize the concentration gradients

Biology 11 Human Biology, TTh 8;00-9:20 Dr. Telleen Transport Through Cell Membranes  Transport through a cell membrane can be:  Active (requiring energy and ATP)  Passive (no energy required)  3 categories of transport  Diffusion (passive)  Carrier-mediated transport (passive or active)  Vesicular transport (active)

Biology 11 Human Biology, TTh 8;00-9:20 Dr. Telleen Diffusion and the Cell Membrane  Diffusion can be simple, channel, or carrier mediated  Channel & carrier mediated diffusion is:  Specific: to size, charge, & interaction with the channel  Subject to saturation: making the channels rate limiting Membrane Transport: Facilitated Diffusion PLAY

Biology 11 Human Biology, TTh 8;00-9:20 Dr. Telleen Active Transport  Active transport proteins:  Move substrates against concentration gradient  Require energy, such as ATP  Ion pumps move ions (Na +, K +, Ca +, Mg 2 + )  Na + -K + Exchange Pump moves both of these ions at the same time, each in the opposite direction (called antiport or countertransport)  Proton Pump uses photosynthesis or food energy to create a proton concentration gradient that then is used to manufacture ATP Active Transport PLAY

Biology 11 Human Biology, TTh 8;00-9:20 Dr. Telleen Sodium-Potassium Exchange Pump  Active transport, carrier mediated:  1 ATP moves 3 Na + out 2 K + in  This creates an electrical potential across the membrane  Called the Transmembrane Potential

Biology 11 Human Biology, TTh 8;00-9:20 Dr. Telleen Transmembrane Potential  Voltage across a membrane  Resting membrane potential – the point where K + potential is balanced by the membrane potential  Ranges from –20 to –200 mV  Results from Na + and K + concentration gradients across the membrane  Differential permeability of the plasma membrane to Na + and K +  Steady state potential is maintained by active transport of ions

Biology 11 Human Biology, TTh 8;00-9:20 Dr. Telleen  Expends metabolic energy to pump protons across membranes Proton Pump (in Mitochondrial Membranes) Proton Pump PLAY

Biology 11 Human Biology, TTh 8;00-9:20 Dr. Telleen Types of Active Transport Primary active transport: hydrolysis of ATP phosphorylates the transport protein causing conformational change Secondary active transport: use of an exchange pump (such as the Na + -K + pump) indirectly to drive the transport of other solutes  Symport system – two substances move across a membrane in the same direction (also called cotransport)  Antiport system – two substances move across a membrane in opposite directions (also called countertransport)

Biology 11 Human Biology, TTh 8;00-9:20 Dr. Telleen Vesicular Transport  Also called bulk transport  Transport of large particles and macromolecules across plasma membranes Directional Descriptive Terms  Exocytosis – moves substance from the cell interior to the extracellular space  Endocytosis – enables large particles and macromolecules to enter the cell  Receptor-mediated  Pinocytosis  Phagocytosis Functional Descriptive Terms  Transcytosis – moving substances into, across, and then out of a cell  Vesicular trafficking – moving substances from one area in the cell to another  Phagocytosis – pseudopods engulf solids and bring them into the cell’s interior

Biology 11 Human Biology, TTh 8;00-9:20 Dr. Telleen Receptor-Mediated Endocytosis  Receptors (glycoproteins called clathrin) bind target molecules (ligands)  Coated vesicle (endosome) carries ligands and receptors into the cell

Biology 11 Human Biology, TTh 8;00-9:20 Dr. Telleen Pinocytosis  Pinocytosis (cell drinking)  Endosomes “drink” extracellular fluid

Biology 11 Human Biology, TTh 8;00-9:20 Dr. Telleen Phagocytosis  Phagocytosis (cell eating)  pseudopodia (psuedo = false, podia = feet)  engulf large objects in phagosomes

Biology 11 Human Biology, TTh 8;00-9:20 Dr. Telleen Exocytosis  Is the reverse of endocytosis

Biology 11 Human Biology, TTh 8;00-9:20 Dr. Telleen Summary  The 7 methods of transport