BIOL 111 1st Edition Lecture 5Outline of Last Lecture I. Cell TypesII. Organization of Eukaryotic cellsIII. Endosymbiosis theoryOutline of Current LectureI. Cell MembranesII. DiffusionIII. OsmosisIV. AquaporinV. Movement across membraneCurrent Lecture- Cell membraneso What is the composition of the cell membrane? Three important components: phospholipid bilayer (amphipathic properties), protiens (amphipathic properties), cholesterol- Amphipathic means have two opposing properties, meaning both hydrophilic and hydrophobic- Proteins are on the outside of the cell and go through the cell- Cholesterol will be in the hydrophobic (inner) part of the cell membrane Freeze fracture preparation - Required the electron microscope because you had to be able to see the cell in that great of detail- In this preparation, the cells had to be frozen and then the top layer was chiseled off with a knife- When the layer was looked at, they saw little bumps on the inside of the layerthat were protiens, showing that there were proteins that were both inside and outside of the membrane o Fluid mosaic model (early 1970s) Fluid—lipids Mosaic—protiens (integral and peripheral) Movement of phospholipids- Lateral movement-movement side to side which occurs approximately 107 times per second- Flip flop movement-switch places across the membrane which occurs once per month Cholesterol-at high temperature=decrease into fluidity, at low temperature=morefluidity (fluidity meter)o Functions of protiens Transport Enzyme activity Signal transduction Cell-to-cell recognition Intercellular joining Attachment to the cytoskeleton and extracellular membrane (ECM)- Cell membraneso Why is selective permeability important?o What is transported in/out of cells?o How is it transported? Hydrophobic or nonpolar?- O2, CO2, steroids Hydrophilic, polar or charged?- Water, protiens, saccharides, ions- Diffusiono Tendency for molecules ot spread out o Down concentration gradiento If across biological membrane via passive transport—no energy requireso Lab examples: potassium permanganate or starch/amylase- Osmosiso Diffusion of water o Down concentration gradient You have to think of what the concentration of the amount of free molecules there are Move from the high concentration of free molecules o Via passive transport—no energy requiredo Across a selectively permeable membrane- Aquaporin o Channel proteins specific for watero Allow fast diffusion through cell membraneo 1st reported 1992 o Discovery awarded 1003 Nobel Prize in chemistry- Related termso Tonicity—property of a solution in reference to a particular membrane Isotonic-not net movement or solutions have equal solute Hypertonic-solution has higher solute compared to other Hypotonic-solution has lower solute compared to other- Movement across membraneo Simple diffusion (passive transport) Direct movement across membrane Down concentration gradient Usually small, hydrophobic (CO2, O2, hydrocarbons) o Facilitated diffusion (passive transport) Transport protiens required Down concentration gradient Used for hydrophilic molecules (polar, ions, etc.) Examples: channel protein, carrier protein, gated channels/ions- Channel protiens are always open and they allow certain substances down their channel- Carrier proteins have to receive the substance to be carried o Active transport Transport protiens required Against concentration gradient—requires ATP Used for any molecule against its concentration gradient- Ex. Sodium potassium channelso Bulk transport Packaging vesicles required Requires ATP Used for large molecules (protiens, polysaccharides- Examples: exocytosis—expelling molecules, endocytosis—uptake of
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