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This 5 page Bundle was uploaded by Christinee on Tuesday February 23, 2016. The Bundle belongs to BIO 201 at University at Buffalo taught by LARA HUTSON in Spring 2016. Since its upload, it has received 65 views. For similar materials see Cell Biology in Biology at University at Buffalo.
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Date Created: 02/23/16
Lecture 12 – Plasma Membrane The Plasma Membrane Compartmentalization o All cells and all domains of life have plasma membranes o Structurally and virtually the same o Make sure biological molecules of life is concentrated enough Scaffolding o Interactions with molecules – sometimes these molecules never find each other o Plasma membranes can hold cells/proteins that need to find each other Selective barrier to diffusion o Maintains appropriate number of ions o Prevents toxins from diffusing in o Selectively permeable Active transport o Proteins for active transport & ions Signaling o Cell has to maintain a certain network of proteins in the plasma membrane o These signals come in the form of molecules o Proteins/peptides/neurotransmitters – none of these can diffuse in plasma membrane o If cell needs to respond, we need to communicate this signal from outside the cell inside the cell Intercellular junctions o Proteins – cell adhesins and integrins hold cells together o Important for multicellular organisms o “gap junctions” (with or without signaling) – useful in heart cells Energy/Metabolism o Membranes contain important proteins for aerobic metabolism and photosynthesis in the case of plants o These proteins are concentrated and held together in these membranes o Talking about inner mitochondrial or chloroplast membrane Electrical transduction o Electrical communication is possible due to plasma membrane and selectively of membrane for ions ▯ ▯ Membrane Structure Bilayer – train track appearance with two dark bands next to each other ▯ ▯ Fatty acids & membrane fluidity Saturated – low in fluidity, high Tm Unsaturated – high in fluidity, low in Tm What we see when we incorporate these into phospholipids in membranes Changing fatty acids – ways that organisms adapt to temperature change ▯ ▯ Cholesterol: membrane antifreeze Large and unusual lipid that’s comproised of lots of carbohydrates Non fatty acid derived lipid Found in membranes Cholesterol by itself has a high Tm, low fluidity Different effect with phospholipid due to antifreeze If you have a membrane at a very high temperature and could potentially melt apart – cholesterol fills in the gaps and makes sure holes don’t appear in membrane and increases van der walls Buffers membrane from very high and very low temperatures Works effectively when it’s at 25% membrane ▯ ▯ Estimated % content of different biological membranes RBC: 50/50 lipid and proteins Myelin: part of nervous systems – not neurons – wrap the axon with lots of membranes serving as an insulin which promotes conductivity – reflected in lipid and protein content Mitochondria/chloroplast: has more proteins – in the business of metabolism ▯ ▯ Membrane structure & proteins Hypothetical model of plasma membrane Lots of proteins and cholesterol There are proteins that go into the fatty acid tails – non polar AA – hydrophobic – integral membrane proteins – span through membrane or insert through parts of membrane Peripheral membrane proteins: sit on membrane and stay on membrane & don’t integrate in layer of membrane Sugars from glycosylation: surfaces exposed to outside of cell – analogous to disulfide bonds o Takes place in golgi complex o These proteins were made in RER ▯ ▯ Fluid mosaic model Membrane amphipathy – phospholipids are amphipathic – interior is hydrophobic and exterior is polar Asymmetric – integral proteins – some proteins inserted on the inside not inserted on the outside – lipids aren’t randomly incorporated into the membrane Fluidity ▯ ▯ Measuring membrane fluidity: (FRAP) Illustrates how proteins might move in the membranes – fluorescent covered proteins Lipids that are in that spot never recover Able to plot the rate of recovery ▯ ▯ Incomplete recovery during FRAP Some cells in some cases showed a very low membrane fluidity – unpredictable Initially steep curve (fluid) – but never got complete recovery ever Little patches of bleached area – remained unfluorescent forever – little holes LIPID RAFTS Lipid Rafts Low fluidity – anchored in place within the membrane – more saturated phospholipids and phospholipids with longer chains Large amounts of cholesterol – too much can increase Tm and decrease fluidity Certain proteins anchored here – integral proteins ▯ ▯ Plasma Membrane permeability Osmosis in RBCs Cells shrink when places in hypertonic solution ▯ ▯ Cells swell or shrink due to osmosis Hypertonic concentration – water concentration is the same on both sides Entropy wants to equalize concentration Membrane isn’t permeable to ions Water flows from inside to outside in an effort to dilute out the solute in order to equalize the concentration Result: lose water and die Determine if ions are the only things that the membrane isn’t permeable too ▯ ▯ Plasma membrane is selectively permeable ▯ ▯ Summer of membrane permeability High to low permeability from top to bottom O, C, N – gases are permeable
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