Membrane Structure Chapter 11 PDF

Today we will talk about membranes & transport across membranes Bilayer thickness is quite constant (~5 nm), but can vary between organelles 50% mass volume are membrane proteins! Repeat of chapter 2: chemical properties of lipid molecules PC = Phosphatidylcholine PE = Phosphatidy...

Today we will talk about membranes & transport across membranes Bilayer thickness is quite constant (~5 nm), but can vary between organelles 50% mass volume are membrane proteins! Repeat of chapter 2: chemical properties of lipid molecules PC = Phosphatidylcholine PE = Phosphatidylethanolamine PS = Phosphatidylserine PI = Phosphatidylinositol Three types of amphipathic lipid molecules in cells Phospholipids Sterols (cholesterol) Glycolipids How hydrophilic parts attract H2O, and hydrophobic repells H2O in on p385-386 Amphipathic = molecule with both a hydrophilic and hydrophobic part  Biophysical properties of a lipid bilayer Energetically favorable to form a ‘vesicle’ Because bilayer thickness is ~5nm, the smallest ‘vesicle’ possible is ~25 nm Lateral diffusion is fast Rotation is super fast Flip-flop is energetically very unfavorable Fluidity of lipid bilayers depends on: The type of lipid ratio saturated vs unsaturated Cholesterol  Phospholipids are synthesized at the ER membrane From symmetric growth… ……to asymmetric reorientation Catalysis Constant flux of cytosolic side newly made Scramblases lipids through randomize secretory lipids in leaflets pathway (CH15) Flippases transfer lipids to other leaflet The end result at the plasma membrane Negative charged phosholipids (PS/PE) on the ‘inside’ cytosolic side Phosphatidylcholine (PS), Spingomyelin, and glycolipids on the extracellular ‘outside’ CH15: positive-inside rule to determine protein topology From lipids to membrane proteins (50% of total mass)! Communication with the outside world (chapter 12) Cell strength Cell-to-matrix and cell-to-cell interaction 60% of the current pharmacological drugs target membrane proteins! How are membrane proteins embedded in the bilayer? A hydrophobic alpha-helix is an optimal sequence in the bilayer  inside outside Cell strength Bacteriorhodopsin Cell cortex of animal cells (red blood cells) Light-activated proton pump Plants / bacteria / fungi use a cell wall for strength CH12: Huge biotechnological potential! Cell-to-Cell recognition: glycolipids & glycoproteins play a major role! In principle the movement of membrane proteins in a cell membrane is free and fast...... In principle the movement of membrane proteins in a cell membrane is free and fast. But in reality, often confined. How can we do research on membrane proteins? Biochemical & structural analysis? Cell biological & microscopical analysis? Free the membrane proteins from the lipid bilayer! Most common detergents we use in biochemistry are (p395): Sodium dodecyl sulfate (SDS) Triton X-100 Carefully balancing how to solubilize membrane proteins (also How we know p400) led to breakthroughs in the field of structural biology on membrane proteins! Fluorescence Recovery After Photobleaching (FRAP) or single-molecule labeling/imaging techniques Automated-tracking software to follow a single molecule labeled membrane protein FRAP  Essential concepts CH11 The chemical properties of the three classes of lipids (slide 3&4) Biophysical properties of lipids and bilayers (slide 5) Symmetric growth of a bilayer and asymmetric redistribution of lipid in a bilayer (slide 7&8) Know some types of membrane proteins (slide 9), how they are embeded in the lipid bilayer (slide 10), and how you can extract them from the bilayer (Slide 17) Movement of membranes proteins in the lipid bilayer (slide 15) and how you can study this (slide 18)