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U-M MCDB 310 - Trans-membrane Proteins, Solute Transferring, and Signal Transduction

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MCDB 310 1st Edition Lecture 13 Outline of Last Lecture I. Steroid HormonesII. VitaminsIII. Lab analysis of lipidsa. Column Chromatographyb. TLCc. Gas Liquid ChromatographyIV. Chapter 11: Biological membranesa. Fluid Mosaic Modelb. Proteins in membranesV. Lipids in membranesOutline of Current Lecture I. Examples of integral, trans-membrane Protein Functiona. Adhesionb. Fusion and Solute transferring (concentration and electrochemical gradients)II. Biochemistry in Cell SignalingCurrent LectureThese 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.I. Examples of Integral, trans-membrane Protein Function: Cell signaling, adhesion, and cell-cell interactionsa. Four classes of adhesion reception proteinsi.All of these are type 3 proteins (except for the one in the box, that one is type 5)ii. Proteins in the box are Integrinsiii. Cadherins have multiple calcium binding domainsiv. N-CAMs have domains that act as antibodiesv. When the ligand binds to these proteins  conformational change  response on the interior of the cellvi. The ones in the box are heterodimeric (made of two different chains)vii. There are many possible combinations of different alpha and beta means many different ways for it to bind to the ligandb. Microdomains (rafts)i. Thicker regions of the membrane enriched in certain proteins and lipids1. High in sphingolipids and cholesterol (which affects fluidity and mobility)2. Lipid linked proteins with 2 palmitoyl or myristoyl groups (long chains  this is what causes them to be thicker)3. Also have GPI-linked proteins are present (these are usually and indication that rafts are present)4. They function as a unit for a specified task5. Caveolae: Span both leaflets of the membrane a. Caveolin is in high concentration (bound to 3 fatty acyl chains per molecule)b. It functions in endocytosisc. These are present in rafts, more easily deformedd. Caveolins form dimers because of weak interactions  cause the caveolae pockets to form  causes vesicles to form that can transport things out of the celle. Ligands also build up in caveolae can eventually pinch off to form vesiclesII. Membrane Function: Fusion and Solute Transporta. Membranes are semi-permeable (control)b. Membrane fusion allows bigger things in or outc. Membrane channels allow smaller things in or outi. Passive Transport is facilitated by membrane proteins1. 2 compartments separated by a membrane with unequal solute concentrations on each side2. All passive transport requires a concentration gradientii. Simple Diffusion: movement of particles until an equilibrium is achieved (movement may not have stopped, but the concentrations on each side are the same)iii. Membrane Potential: an ELECTRICAL gradient (caused by an unequal distribution of a charged solute)1. Solutes move until particles reach a charge equilibrium2. Vm=Membrane Potential (Vm=0 at equilibrium, however, this does not mean that the concentrations of the solute are equal, but the system has reached a charge equilibrium)iv. Electrochemical Gradient: Electrical charge and solute concentrations are NOT equal 1. To get through a membrane, any solute must:a. Strip away its solvation layer (outer layer)b. Moving past the hydrophobic region of a membranec. Rehydrate2. This process is very slow, and it requires energy3. The amount of energy is so high that membranes are virtually impenetrable to polar solutes4. Need a different mechanism: Protein with a charged channel in the middlea. Non-polar amino acids interact with non-polar region of membrane, and charged amino acids are on the insidev. Facilitated Diffusion: requires a protein transporter (but not necessarily energy, still a form of passive transport)1. Uniport: only one solute is transported2. Symport: 2 different solutes move in the same direction3. Antiport: 2 different solutes move in opposite directions4. The general class of these are transporters or permeasesa. Span the membrane, sometimes many timesb. Bind with specificityc. Bind using weak interactions5. Example: Glucose Transporter (GLUT 1) a. Structure: Type III membrane protein with 12 trans-membrane domains (polar domains inside the membrane in order to facilitate transport of polar solutes)b. Put 5 of these molecules together to make a transporter with a polar core on the inside and non-polar acyl chains on the outsidec. This structure facilitates transport of glucose with hydrogen bonding (very specific-must be the right size andhave the ability to form 4 hydrogen bonds in the correct spot)d. To stop glucose from being transported, turn the 5 molecules (like a gear) and nothing is able to go through the channele. Function:i. Glucose binds to the transporter (high affinity for glucose)ii. There is a conformational change in the transportermolecule causing a change in affinity (lowers it)iii. Glucose is released inside the celliv. There is a reverse conformational change back to the initial statef. Kinetic Mechanism: Analogous to enzyme catalyzed reactionsi. Can use this final equation to solve for any of the unknownsii. Plot it just like a michaelis-menton plot (initial velocity of entry vs concentration of solute on the outside of the cell) iii. Can plot with a lineweaver-burke plot as well to getmore exact Vmax and Kt6. Example 2: Erythrocyte Anion Exchanger (Cotransport of Cl- and bicarbonate, both of which are negatively charged)a. This is an example of facilitated diffusionb. Respiring tissues are making carbon dioxide (toxic)  converted to bicarbonate in red cells (transportable, safe, and it acts as a buffer)c. Bicarbonate can move out of the blood cell to act as a buffer in the blood (passive transport, simple diffusion)d. In the lungs, the reverse reaction takes place in the blood cells to convert bicarbonate back into CO2 which again will naturally diffuse out of the celle. There is no change in charge (Vm) across this membranevi. Active Transport: Requires energy to push solutes against their concentration or electrochemical gradient (often requires a facilitator of some kind)1. Thermodynamically favored only if coupled to an exergonic process such as absorption of light, redox, or a breakdown of ATP (not hydrolysis, but phosphorylation)2. Sometimes a facilitator hydrolyzes ATP to get -30 kilojoules of energy (a lot) to pump things against this barrier3. Primary active transport: solute transport against its


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