Lecture 3 Notes
Lecture 3 Notes Biol-K416
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This 5 page Class Notes was uploaded by Malissa Notetaker on Tuesday September 13, 2016. The Class Notes belongs to Biol-K416 at Indiana University Purdue University - Indianapolis taught by Dr. Jason Meyer in Fall 2016. Since its upload, it has received 4 views. For similar materials see Cell & Molecular Neuroscience in Neuroscience at Indiana University Purdue University - Indianapolis.
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Date Created: 09/13/16
Cellular and Molecular Neuroscience Lecture 3 8/29/16 Topic: Membrane Structure and Transport ● Cell plasma membrane structure: ○ Proteins ○ Lipids ■ Should NOT see tails. Why? ● Tails are hydrophobic ● Plasma membrane is a highly fluid structure ○ Why is this important? ■ For endo/exocytosis ■ Protein movement on membrane ■ Cell division ■ Growth and shrinkage ■ Could break if too rigid ■ Able to reform itself in response to different stimuli ■ Able to withstand a lot to protect insides ● Phospholipides most abundant lipids in neuronal membranes ○ Fluidity determined by length of tails as well as presence of cis bonds ■ Cis bonds give curvature ○ Amphiphilic contain both hydrophobic and hydrophilic regions ■ Hydrophobic “waterhating” ■ Hydrophilic “watertolerating” ○ Phosphoglycerides ■ 3carbon glycerol backbone ■ Most common phospholipids ● Organization of lipids ○ Lipid micelle ■ Arranged in spherical fashion ○ Lipid bilayer ○ Hydrophobic tails control the orientation due to “hatred” ● How is the lipid bilayer typically arranged? ○ Planar phospholipid bilayer w/ edges exposed to water is energetically unfavorable ○ Sealed compartment formed by phospholipid bilayer is energetically favorable ■ Called liposome ○ What is the difference between liposome and micelle? ■ Liposome has bilayer, micelle does not ○ Liposomes can be used to deliver stuff to cell ■ Many proteins ○ What is the difference between a liposome and a vesicle? ■ Liposome just lipids ■ Vesicles more than lipids, proteins ● Mobility of Phospholipid Molecules ○ Types of movement: ■ Lateral diffusion ■ Flexion ■ Rotation ■ Flip flop ● Rarely occurs b/c tail regions are exposed only happens when enzymes are in place to protect tails ● Signaling Functions of Inositol Phospholipids ○ Inositol phospholipids present in small quantities, but have important functions in guiding membrane traffic and in cell signaling ● Types of Membrane Proteins ○ Span across, pass through many times, form pores, one side, link together to form complex ○ Helps determine function of proteins ● Diffusion of proteins in plasma membrane ○ Fuse together two different cell lines ■ Ex: mouse & human ○ Fused cell is now a heterocaryon ○ Use antibodies against mouse membrane protein labeled with fluorescein, antibodies against human membrane protein labeled with rhodamine ■ Initially antibodies will be split half on one side, half on the other side ■ A 7fter incubation (37 C) ~ 40 min, the proteins will blend ○ Purpose is to show that the proteins are mobile ● Photobleaching experiments to confirm lateral diffusion of membrane proteins ○ FRAP Fluorescence Recovery After Photobleaching ■ Use laser beam to bleach an area ■ Use the time it take the spot’s color to recover to tell how mobile the proteins are in the membrane ○ FLIP Fluorescence Loss In Photobleaching ■ Use laser beam to bleach an area ■ Continue bleaching area, use the time it takes for the whole cell to lose color to see how mobile the proteins are in the membrane ● Not ALL proteins are mobile, some could be anchored to the cytoskeleton ○ Receptors in dendrites to receive signals ● Confining Proteins to Specific Domains ○ Epithelial cells are meant to serve as a protective barrier ■ Certain proteins may help by fusing the cells together are supposed to be in a specific locations ○ Membrane Support ■ What kinds of substances would need to be transported across the membrane? ● MAP2 found in cell body and dendrites ● Neurofilament found in axons ○ There were no overlap of the colors, showing that the two are separate ● Conductance across neuronal membranes ○ Lipids form the bilayer ○ Na cannot get in ■ Needs Na channel ○ Oxygen can get right in ○ Water cannot get in ■ Needs aquaporin ○ Glucose cannot get in ■ Needs glucose transporters ○ Na can come out ■ Needs Na/K pump ● Electrochemical gradient ○ Electrochemical gradient with no membrane potential, some will move across gradient depending on concentration ○ Electrochemical gradient with membrane potential negative inside (positive neurons outside), will try and push the + ions into the cell because less concentration and negative charge ○ Electrochemical gradient with membrane potential positive inside, will not want to come inside much because the charge is positive on the inside ○ The Electrochemical Gradient is dependent on both the membrane potential AND the concentration gradient ● Two main classes of membrane transport proteins ○ Transporters binds solute and undergoes conformational change to transfer solute across membrane ■ Imbedded in membrane ■ Slower than channels ● Only allows one or two at a time ○ Channels form aqueous pores that extend across bilayer. When open, they allow specific solutes to pass through ■ Specificity conferred to channels by using the size and charge of individual ions ● Electrochemical gradient decides what goes through ■ Faster that transporters, can just rush in ● Passive vs. Active Transport ○ Neither simple molecules (like oxygen) can use simple diffusion ○ Passive Transport channelmediated or transportermediated that does NOT require energy ○ Active Transport transporter that REQUIRES energy ■ Needs energy bc going across gradient high conc. to low conc. ● Active Membrane Transport ○ Uniport can assist in moving one molecule across gradient ○ Symport can move two molecules across gradient in the same direction ○ Antiport can move two molecules across gradient in opposite directions ○ Coupled transporters couple uphill transport of one solute across the membrane to the downhill transport of another ■ Uses energy provided by one to move another even though against gradient ○ ATPdriven pumps couple uphill transport to the hydrolysis of ATP ○ Lightdriven pumps couple uphill transport to an input of energy from light ● Na+/K+ Pump ○ An active transporter ○ Is most influential at resting membrane potential, why can hold @ 70, always exchanging 3 Na+ for 2 K+
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