BMB 251 1st Edition Lecture 29 Outline of Last Lecture I. Clicker QuestionII. PhosphoglyceridesIII. Different types of Phospholipids IV. Cholesterol V. GlycolipidsOutline of Current Lecture VI. Lipid bilayer ProteinsVII. Transmembrane ProteinsVIII. Cytosolic ProteinsIX. Noncytosolic ProteinsX. Types of Transmembrane ProteinsXI. Sugar-Coated MembranesCurrent Lecture- Lipid bilayer provides a basic structure for the membranes, but proteins perform membrane’s specific tasks, giving each cell membrane its characteristic functional properties- In a cell membrane that is 50% proteins by mass, there is 50 lipid molecules for every one protein lipids are extremely small- Transmembrane proteins: amphiphilic proteins extending through lipid bilayer, with part of protein on either sideo Hydrophobic regions pass through membrane and interact with the hydrophobic lipid tailso Hydrophilic regions are exposed to the water on either sideo Integral membrane proteins: within the hydrophobic core of lipid bilayer and cannot be easily released o Only proteins that can function on BOTH sides of the bilayer and transport molecules across ito Unique orientation with membrane because of the asymmetric manner in which it is inserted into the lipid bilayer in ER during its biosynthesis- Other proteins can be located entirely in cytosol, with either and amphiphilic alpha helix exposed on the surface of proteins or by one or more covalently attached lipid chains o Peripheral membrane proteins: can be released from membrane by relatively gentle extraction measures, such as extreme change in pH or exposure to high or low ionic strength to interfere with protein-protein interactions - Other membrane proteins are attached at the external surface via covalent linkage to a specific oligosaccharide to phosphatidylinositol on outer lipid monolayerThese 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.o Transmembrane segment is cleaved off at ER and replaced with glycosylphosphatidylinositol (GPI) anchor, which solely binds to noncytosolic surface- Single-pass transmembrane proteins: polypeptide chain only crosses once - Multipass transmembrane proteins: polypeptide chain crosses multiple times- Beta barrel: mulitpass transmembrane structure used in porin (transport) proteins o More rigid and they crystallize readilyo Abundant in mitochondria, chloroplasts and many bacteriao Some are pore-forming proteins create water channels that allow small hydrophilic molecules to cross the bilayer- Many transmembrane proteins are glycosylated oligosaccharide chains are always present on noncytosolic side of membraneo Carbohydrates coat the surface of all eukaryotic cells occur as oligosaccharides covalently bind to membrane proteins (glycoproteins) and lipids (glycolipids) Aka cell coat or
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