AP Biology Go to the “Free Response Help” link on my website to check out the Unit 2 FRQs!!!

AP Biology Pre-Lab Preparation!!!  Go to “Labs & Lab Notebook” link on my website.  Click on “LabBench” link.  Click on “Lab 1: Diffusion & Osmosis.”  Read through Concepts #1-5, Design Exercises #1-2, and Self-Quiz ?s #1-3 of the Pre-Lab.  Answer the general questions COMPLETELY that are listed on your Lab Notebook Guidelines sheet.  Remember to ignore the “Water Potential” section and calculations  Due on Friday!!!

AP Biology The Cell Membrane

AP Biology Arranged as a Phospholipid bilayer polar hydrophilic heads nonpolar hydrophobic tails polar hydrophilic heads  Serves as a cellular barrier / border impermeable to polar molecules

AP Biology Cell membrane defines cell  Cell membrane separates living cell from aqueous environment  But…separation CANNOT be complete, or the cell would die!  Controls traffic in & out of the cell  allows some substances to cross more easily than others  hydrophobic (nonpolar) particles can cross more easily than vs. hydrophilic (polar) particles

AP Biology Permeability to polar molecules?  Membrane becomes “semi-permeable” via protein channels  specific channels allow specific material across cell membrane inside cell outside cell sugaraa H2OH2O salt NH 3

AP Biology Cell membrane is more than lipids…  Transmembrane proteins embedded in phospholipid bilayer  create semi-permeable channels lipid bilayer membrane protein channels in lipid bilyer membrane

AP Biology Classes of amino acids nonpolar & hydrophobic

AP Biology Classes of amino acids polar & hydrophilic

AP Biology Membrane Proteins  Within membrane  nonpolar amino acids  hydrophobic  anchors protein into membrane  On outer surfaces of membrane in fluid  polar amino acids  hydrophilic  extend into extracellular fluid & into cytosol Polar areas of protein Nonpolar areas of protein

AP Biology NH 2 H+H+ COOH Cytoplasm Retinal chromophore Nonpolar (hydrophobic)  -helices in the cell membrane H+H+ Porin monomer  -pleated sheets Bacterial outer membrane proton pump channel aquaporin = water channel Examples H2OH2O H2OH2O H+H+ H+H+

AP Biology Many Functions of Membrane Proteins Outside Plasma membrane Inside Transporter Cell surface receptor Enzyme activity Cell surface identity marker Attachment to the cytoskeleton Cell adhesion “Antigen” “Channel”

AP Biology Membrane is a collage of proteins & other molecules embedded in the fluid matrix of the lipid bilayer Extracellular fluid Cholesterol Cytoplasm Glycolipid Transmembrane proteins Filaments of cytoskeleton Peripheral protein Glycoprotein Phospholipids Fluid Mosaic Model

AP Biology Parts of the “mosaic”…  Fat composition affects flexibility  membrane must be fluid & flexible  % unsaturated fatty acids in phospholipids  keep membrane more fluid  Cold weather plants = increased unsaturated fatty acids (“winter wheat”)  cholesterol in membrane  prevents membrane from “freezing”

AP Biology Membrane carbohydrates  Play a key role in cell-cell recognition  ability of a cell to distinguish one cell from another  antigens  basis for rejection of foreign cells by immune system

AP Biology Movement across the Cell Membrane

AP Biology Diffusion  2nd Law of Thermodynamics governs biological systems  universe tends towards disorder (entropy)  Diffusion  movement from HIGH  LOW concentration  Diffusion  movement from HIGH  LOW concentration

AP Biology Simple Diffusion  Move from HIGH to LOW concentration  “passive transport”  no energy needed diffusionosmosis movement of water

AP Biology (a) Diffusion of one solute. The membrane has pores large enough for molecules of dye to pass through. Random movement of dye molecules will cause some to pass through the pores; this will happen more often on the side with more molecules. The dye diffuses from where it is more concentrated to where it is less concentrated (called diffusing down a concentration gradient). This leads to a dynamic equilibrium: The solute molecules continue to cross the membrane, but at equal rates in both directions. Diffusion of two solutes. Solutions of two different dyes are separated by a membrane that is permeable to both. Each dye diffuses down its own concen- tration gradient. There will be a net diffusion of the purple dye toward the left, even though the total solute concentration was initially greater on the left side. (b) Osmosis Molecules of dye Membrane (cross section) WATER Net diffusion Equilibrium Net diffusion Equilibrium

AP Biology Facilitated Diffusion  Diffusion through protein channels  channels move specific molecules across cell membrane  no energy needed open channel = fast transport facilitated = with help HIGH LOW

AP Biology Active Transport conformational change  Cells may need to move molecules against concentration gradient  conformational shape change transports solute from one side of membrane to other  protein “pump”  “costs” energy = ATP

AP Biology Active transport ATP

AP Biology Getting through cell membrane  Passive Transport  Simple diffusion  diffusion of nonpolar, hydrophobic molecules  lipids  HIGH  LOW concentration gradient  Facilitated transport  diffusion of polar, hydrophilic molecules  through a (hydrophilic) protein channel  HIGH  LOW concentration gradient  Active transport  diffusion against concentration gradient  LOW  HIGH  uses a transport protein  A.K.A. “protein pump”  requires ATP ATP

AP Biology Transport summary simple diffusion facilitated diffusion active transport ATP

AP Biology How about large molecules?  Moving large molecules into & out of cell  through vesicles & vacuoles  endocytosis  phagocytosis = “cellular eating”  pinocytosis = “cellular drinking”  Exocytosis  Example:  Pancreas cell secreting insulin into bloodstream exocytosis

AP Biology Endocytosis phagocytosis pinocytosis receptor-mediated endocytosis fuse with lysosome for digestion non-specific (takes in all molecules in extra-cellular fluid) triggered by molecular signal

AP Biology The Special Case of Water Movement of water across the cell membrane

AP Biology Osmosis is just diffusion of water  Water is very important to life, so we talk about water separately  Diffusion of water from HIGH concentration of water to LOW concentration of water  across a semi-permeable membrane

AP Biology Concentration of water  Direction of osmosis is determined by comparing total solute concentrations  Hypertonic - more solute, less water  Hypotonic - less solute, more water  Isotonic - equal solute, equal water hypotonichypertonic water net movement of water

AP Biology freshwaterbalancedsaltwater Managing water balance  Cell survival depends on balancing water uptake & loss

AP Biology Managing water balance  Hypotonic  a cell in fresh water  high concentration of water around cell  problem: cell gains water, swells & can burst  example: Paramecium  ex: water continually enters Paramecium cell  solution: contractile vacuole  pumps water out of cell  “osmoregulation”  plant cells  turgid = full  cell wall protects from bursting freshwater

AP Biology Pumping water out  Contractile vacuole in Paramecium ATP

AP Biology Managing water balance  Hypertonic  a cell in salt water  low concentration of water around cell  problem: cell loses water & can die  example: salinity increases in lake  plant cells  plasmolysis = wilt  can recover if conditions change saltwater

AP Biology Managing water balance  Isotonic  animal cell immersed in mild salt solution  no difference in concentration of water between cell & environment  problem: none  no net movement of water flows across membrane equally, in both directions  cell in equilibrium  volume of cell is stable  example: blood cells in blood plasma  slightly salty IV solution in hospital balanced

AP Biology Aquaporins protein channels allowing rapid flow of water across cell membrane explains efficient nature of osmosis

AP Biology Cell (compared to beaker)  hypertonic or hypotonic Beaker (compared to cell)  hypertonic or hypotonic Which way does the water flow?  in or out of cell.05 M.02 M Do you understand Osmosis…