LIFE 102 1st Edition Lecture 11 Outline of Last Lecture I. Cell membranes are fluid mosaics of lipids and proteinsII. Transport of molecules over membranesIII. Membrane transport of proteinsIV. Membrane transport of most macromoleculesOutline of Current Lecture (CH. 7 part two)I. Phospholipid bilayer is a selective barrierII. Active transportIII. Cotransporters couple active and passive transportIV. Transport of particles and large moleculesCurrent LecturePhospholipid Bilayer is a selective barrierI. Molecules that can diffuse across the lipid bilayer (without help of proteins)A. Non-polar moleculesa. O2 , CO2, hydrocarbonsB. Small, uncharged polar moleculesa. H2OC. Larger polar molecules and ions need transport proteins to get across membraneII. Osmosis: passive diffusion of water across a selectively permeable membraneA. Solutes that DON’T cross the membrane drive osmosisB. Water diffuses toward the highest solute concentrationC. Which mean it’s going towards the lowest free water concentrationa. Remember: Water follows SoluteD. Water balance of cells without wallsa. Tonicity: the ability of a surrounding solution to cause a cell to gain or lose waterb. Isotonic solution: solute concentration is the same as that inside the cell; no net water movement across the plasma membraneThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.c. Hypertonic solution: solute concentration is greater than inside the cell; cell loses waterd. Hypotonic solution: solute concentration is less than that inside the cell; cell gains waterE. Animal cells prefer an isotonic environmenta. Too little water and they shrivel, too much and they burst F. Plant cells prefer a hypotonic environmenta. They want water to flow into the cell to keep them Turgid (sturdy), they don’tburst because they have a cell wallIII. Facilitated Diffusion through proteins “Passive Transport” A. Faster than regular diffusionB. Allows ions and large polar molecules to crossC. Uses Channel Proteins:a. Specific hydrophilic tunnel across membraneb. Many are gated and open by stimulusc. Example: Aquaporins (water channels), they retain water in your kidneysD. Use Carrier Proteins:a. Pass specific substances down concentration gradient through changes in the shape of the membrane proteinb. They shift their binding site (translocate) across the membrane and the substance is releasedActive transport I. Through proteins:A. Moves molecules against concentration gradient (requires energy)B. ATP’s terminal phosphate is transferred to the membrane proteinC. Includes change in protein shape, moving molecule across membraneII. Through protein ion pumpsA. Creates a membrane potential: voltage difference across a membranea. Like a batteryb. Also called electrogenic pumpsB. Create electrochemical gradientsa. Two forces that act on ionsi. Ion’s concentration gradient (so…diffusion)ii. Effect of membrane potential on ion’s movement (if the inside of the cell has an over all positive charge, than negative ions on the outside will be attracted to it)Cotransporters couple active and passive transportI. The gradient created by the active transport of one molecule can move a second molecule UP its concentration gradientA. Plants: Load glucose into the veins of leaveB. Animals: Na+ /Glucose cotransporter keeps Na levels upTransport of particles/Large molecules (like proteins, polysaccharides, complex particles)I. Packaged in vesiclesA. Exocytosis: Secretion of content via fusion with membrane (exits the cell)B. Endocytosis: Captures content from outside the cell, new vesicles are formed (substances enter the cell)a. Types of endocytosis:i. Phagocytosis: cell engulfs a particle and forms a food vacuole, which is digested by a lysosome1. “Cell-eating”ii. Pinocytosis: cell captures extra cellular fluid (which contains dissolvedsolutes)1. “Cell-drinking”iii. Receptor mediated endocytosis: Cell acquires a specific substance that is found in low abundance1. That substance binds to receptors made just to fit