BIOL 111 1st Edition Lecture 5 Outline of Last Lecture I Cell Types II Organization of Eukaryotic cells III Endosymbiosis theory Outline of Current Lecture I Cell Membranes II Diffusion III Osmosis IV Aquaporin V Movement across membrane Current Lecture Cell membranes o 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 layer that 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 10 7 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 more fluidity 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 membranes o 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 Diffusion o Tendency for molecules ot spread out o Down concentration gradient o If across biological membrane via passive transport no energy requires o Lab examples potassium permanganate or starch amylase Osmosis o 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 required o Across a selectively permeable membrane Aquaporin o Channel proteins specific for water o Allow fast diffusion through cell membrane o 1st reported 1992 o Discovery awarded 1003 Nobel Prize in chemistry Related terms o 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 membrane o 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 channels o Bulk transport Packaging vesicles required Requires ATP Used for large molecules protiens polysaccharides Examples exocytosis expelling molecules endocytosis uptake of molecules
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