BMB 462 Lecture 3 Outline of Last Lecture I Introduction to Membrane lipids a Basic Structure b Basic properties II Classes of Membrane lipids a Glycerophospholipids b Galactolipids Sulfolipids c Sphingolipids d Sterols e Isoprenoids III Lipase activity IV Lipid Signaling Outline of Current Lecture I Experimentation with Lipids II Membrane Function III Membrane Structure Composition a Common features b Lipid Composition c Fluid Mosaic Model d Protein Composition IV Introduction to Hydropathy Plots Current Lecture Concepts to remembers from previous courses lectures GLC and HPLC procedures Amino Acid structures and properties polar amino acids vs hydrophobic amino acids I Experimentation with Lipids a Lipids are poorly soluble in H2O so when separating out lipids you need them to end in an organic solvent i Proteins nucleic acids etc would end up in the aqueous solution b Isolation of Lipids Using Organic Solvents These 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 Lipids are hydrophobic so they partition into hydrophobic organic solvents ii Neutral lipids are extracted with nonpolar solvents like chloroform iii Membrane lipids are extracted with more polar organic solvents i e methanol that weaken both the hydrophobic and electrostatic interactions c Separation via Absorption Chromatography or Thin Layer Chromatography TLC i Once you ve separated the lipids from the rest of the cell components you need to separate the different types of lipids ii Differences in solubility in nonpolar solvents or polarity of different lipids allows separation iii Polar lipids bind to the silica while neutral lipids move into the organic solvent iv Increasing the polarity of the solvent removes increasingly polar lipids v Chromatography is based on partitioning between a nonpolar mobile phase which gets increasingly more polar and a polar stationary phase d Determination of chain length and saturation by GLC or HPLC mass spectrometer protocols e Determination of fatty acid position by enzymatic degradation f Determination of double bond positions mass spec Beginning of unit on Membrane Function Structure and Dynamics II Membrane Function a Membranes regulate what crosses into out of the cell i They are semi permeable transport proteins aid in movement of molecules b They set boundaries and compartments within the cell c They can organize complex reactions allowing communication and energy generation i Receptor proteins in membranes are important for detecting signals ii The 2D surface of membranes increases molecular interactions and increases efficiency d Exocytosis Endocytosis possible because membranes can break and reseal III Membrane Structure Composition a Common features i Sheet like structures 5 8nm thick ii Amphipathic arranged in lipid bilayer iii Membrane components are not covalently bound but are linked by noncovalent interactions that allow the membrane to remain fluid iv Consist of polar lipids and proteins these often have carbohydrates attached v Asymmetric vi Electrically polarized b Lipid Composition i Membranes are composed of different types and ratios of proteins phospholipids sterols and other lipids according to what tissue they are a part of and what molecules they need 1 e g Why would you need more proteins in a bacterial membrane than in a human myelin sheath E coli has to have more of a barrier to protect itself from the environment Most of E coli s energy comes from the membrane it comes from mitochondria in the myelin sheath the membrane in myelin is typically just insulation ii Most common lipids in almost all membranes sphingolipids phosphatidylcholine phosphatidylethanolamine iii A lot of proteins in the membranes means the membrane has a lot of activity functions iv Cells have a way of targeting and maintaining lipids in the membrane the lipid membrane has important functions according to associated tissue 1 Basic membrane functions protection structure etc membranes also have tissue specific needs specific functions 2 There is a functional importance to the side of the membrane a phospholipid is on a e g if Phosphatidylserine is in the inner leaflet everything in the cell is ok If the cell is dying and degrading it will signal this to other cells by switching PS to the outer leaflet This signals surrounding cells that the cell is going to degrade which brings the other cells in to help with apoptosis or get clear of the area v In the bilayer of the membrane the inner facing cytosol and outer facing external environment leaflets the composition is asymmetrical 1 Components in the outer leaflet are different from those found in the inner leaflet a Due to random flip flopping of membrane components it would seem logical that there would eventually be an even distribution of all molecules This doesn t happen though because the cell exerts effort to maintain asymmetry c Fluid Mosaic Model i Components are lipids proteins peripheral integral lipid linked carbohydrates linked to protein or lipid on the outer face ii Movement accounts for the fluid portion the components are not static or rigid but move laterally along the same leaflet or transversely across leaflets 1 Lipids are not bound covalently they rely on hydrogen bonding Van der Waals interactions etc to stay together 2 Lateral movement happens frequently and easily transverse movement is more difficult for the cell because the polar head has to move through the hydrophobic area to get to the other side and happens much less commonly iii Asymmetry accounts for the Mosaic portion of the model d Protein Composition i There are 3 types of membrane proteins peripheral integral lipid linked 1 Peripheral Proteins a These are only found on the polar surface of the membrane b They are held in place by electrostatic interactions and hydrogen bonds they don t penetrate into the hydrophobic core they interact mostly with the polar heads c Peripheral proteins can be removed by causing changes in salt concentration or pH i These are very mild treatments that don t largely impact the membrane ii Adding detergent or an organic solvent would disrupt the membrane and make it too difficult to separate the peripheral protein from other membrane proteins components 2 Integral Proteins a Transmembrane proteins that extend through the hydrophobic portion and extend out into the environment on both sides of the membrane b They can
View Full Document
Unlocking...