BMB 251 1st Edition Lecture 28 Outline of Last Lecture I. Clicker QuestionII. Plasma MembraneIII. Lipid BilayerIV. PhospholipidsOutline of Current Lecture V. Clicker QuestionVI. PhosphoglyceridesVII. Different types of Phospholipids VIII. Cholesterol IX. GlycolipidsCurrent Lecture- Clicker Question 1: In a membrane bilayer, amphipathic lipids are free to move in various ways. Which of the following types of movement is least likely to occur?o Flip-flop- Phosphoglycerides: two long fatty acids linked through ester bonds to adjacent carbon atoms of the glycerol; third carbon atom is attached to a phosphate group (which can be linked to several differed types of head groups)o Main types in mammalian cell membranes: Phosphatidylethanolamin, phosphatidylserine, phosphatidylcholine- Another important phospholipid is the sphingomyelin (created from sphingosine instead of glycerol) o Contains long acyl chain with an amino group (NH2) and two hydroxyl groups (OH) o Differs from phosphoglycerides because it does not attach to glycerol and contains a phosphocholine group and fatty acid tail instead of two fatty acid tails- In addition to phospholipids, cell membranes also contain cholesterol and glycolipids- Cholesterol o Rigid ring structure with one polar –OH group and short hydrocarbon tailo Orient themselves in the bilayer with their –OH group close to the head groups of adjacent phospholipid molecules- Shape and amphiphilic nature of phospholipids form bilayers spontaneously in aqueous environments o Spontaneously aggregate to bury the hydrophobic hydrocarbon tails in the interior and expose the hydrophilic heads- Cholesterol modulates properties of lipid bilayer to: when mixed with phospholipids, it enhancesthe permeability-barrier properties of bilayer to small water-soluble moleculesThese 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 Tightens packing of bilayer, but does not make the membrane any less fluido Fluidity of lipid bilayer depends on its composition and temperatureo Can also prevent hydrocarbon chains form coming together and crystallizing - Lipid rafts: plasma membrane that transiently assembles into specialized domains, which appear thicker then rest of the bilayer due to longer and straighter hydrocarbon tails on the sphingolipids o Help organize membrane proteins (transport through vesicle or working in protein assemblies) or converts extracellular signals into intracellular ones- Most cells store excess lipids in lipid droplets, from which they can be retrieved as building blocks for membrane synthesis or as a food source- Lipid bilayer is asymmetric, having different head groups and charges important for turning extracellular signals into intracellular ones, recruiting proteins that guide membrane transport, distinguish between live and dead cells (in animals) by phosphotidylserine rapidly translocating to the extracellular monolayer up cell death, where it signals for macrophages to come and digest it- Glycoplipids: sugar-containing lipids found on noncytosolic monolayer of lipid bilayer o Made from sphingosineo Have most extreme asymmetric o Important roles in interactions of the cell with its surroundingso Gangliosides are the most complex of the glycolipids, with a net negative chargeo Function in cell-recognition processes (cell-cell adhesion)- Phase transition: bilayer changes from liquid to semi-solid gel; temperature to do this becomes lower if the hydrocarbons are short or have double
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