英文脂和生物膜.pptx

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1、Lipids and Membranes第1页/共27页Lipids Lipids:Lipids:a heterogeneous class of naturally occurring organic compounds classified together on the basis of common solubility propertiesinsoluble in water,but soluble in aprotic organic solvents including diethyl ether,chloroform,methylene chloride,and acetone

2、Lipids includefatty acids,triacylglycerols,sphingolipids,phosphoacylglycerols,glycolipids,lipid-soluble vitaminsprostaglandins,leukotrienes,and thromboxanescholesterol,steroid hormones,and bile acids第2页/共27页Fatty Acids Fatty acidFatty acid:an unbranched-chain carboxylic acid,most commonly of 12-20 c

3、arbons,derived from hydrolysis of animal fats,vegetable oils,or phosphodiacylglycerols of biological membranesIn the shorthand notation for fatty acidsthe number of carbons and the number of double bonds in the chain are shown by two numbers,separated by a colon第3页/共27页Fatty Acids第4页/共27页Fatty Acids

4、Among the fatty acids most abundant in plants and animalsnearly all have an even number of carbon atoms,most between 12 and 20,in an unbranched chainthe three most abundant are palmitic(16:0),stearic(18:0),and oleic(18:1)acidsin most unsaturated fatty acids,the cis isomer predominates;the trans isom

5、er is rareunsaturated fatty acids have lower melting points than their saturated counterparts;the greater the degree of unsaturation,the lower the melting point第5页/共27页Triacylglycerols Triacylglycerol(triglyceride)Triacylglycerol(triglyceride):an ester of glycerol with three fatty acidsnatural soaps

6、 are prepared by boiling triglycerides(animal fats or vegetable oils)with NaOH,in a reaction called saponification(Latin,sapo,soap)第6页/共27页SoapsSoaps form water-insoluble salts when used in water containing Ca(II),Mg(II),and Fe(III)ions(hard waterhard water)第7页/共27页Phosphoacylglycerols Phosphoacylgl

7、ycerolsPhosphoacylglycerols(phosphoglycerides)are the second most abundant group of naturally occurring lipidsfound almost exclusively in plant and animal membranes,which typically consist of 40%-50%phosphoacylglycerols and 50%-60%proteinsthe most abundant phosphoacylglycerols are derived from phosp

8、hatidic acid,a molecule in which glycerol is esterified with two molecules of fatty acid and one of phosphoric acidthe three most abundant fatty acids in phosphatidic acids are palmitic(16:0),stearic(18:0),and oleic(18:1)第8页/共27页PhosphoacylglycerolsA phosphatidic acidfurther esterification with a lo

9、w-molecular-weight alcohol gives a phosphoacylglycerolthe most common of these low-molecular-weight alcohols are第9页/共27页Phosphoacylglycerols第10页/共27页Phosphoacylglycerols第11页/共27页PhosphoacylglycerolsA lecithin第12页/共27页WaxesAn ester of a long-chain fatty acid and alcoholfrom the Old English word weax=

10、honeycomb第13页/共27页Sphingolipidscontain sphingosine,a long-chain aminoalcohol from which this class is named第14页/共27页Glycolipids GlycolipidGlycolipid:a compound in which a carbohydrate is bound to an-OH of the lipidmany glycolipids are derived from ceramides第15页/共27页Steroids SteroidsSteroids:a group

11、of plant and animal lipids that have this tetracyclic ring structure第16页/共27页SteroidsThe features common to the ring system of most naturally occurring steroids are illustrated here 第17页/共27页Androgens Androgens:Androgens:male sex hormonessynthesized in the testesresponsible for the development of ma

12、le secondary sex characteristics第18页/共27页Estrogens Estrogens:Estrogens:female sex hormonessynthesized in the ovariesresponsible for the development of female secondary sex characteristics and control of the menstrual cycle第19页/共27页CholesterolThe steroid of most interest in our discussion of biologic

13、al membranes is cholesterol 第20页/共27页Biological MembranesIn aqueous solution,phosphoglycerides spontaneously form into a lipid bilayer,with a back-to-back arrangement of lipid monolayers(see Figure 7.10)polar head groups are in contact with the aqueous environmentnonpolar tails are buried within the

14、 bilayerthe major force driving the formation of lipid bilayers is hydrophobic interactionthe arrangement of hydrocarbon tails in the interior can be rigid(if rich in saturated fatty acids)or fluid(if rich in unsaturated fatty acids)第21页/共27页Biological MembranesFigure 7.10 A lipid bilayer 第22页/共27页B

15、iological Membranesthe presence of cholesterol increases rigiditywith heat,membranes become more disordered;the transition temperature is higher for more rigid membranes;it is lower for less rigid membranesplant membranes have a higher percentage of unsaturated fatty acids than animal membranesthe p

16、resence of cholesterol is characteristic of animal rather than plant membranesanimal membranes are less fluid(more rigid)than plant membranesthe membranes of prokaryotes,which contain no appreciable amounts of steroids,are the most fluid第23页/共27页Membrane Proteins FunctionsFunctions:transport substan

17、ces across membranes;act as receptor sites,and sites of enzyme catalysisPeripheral proteinsbound by electrostatic interactionscan be removed by raising the ionic strengthIntegral proteinsbound tightly to the interior of the membranecan be removed by treatment with detergents or ultrasonificationremo

18、val generally denatures them第24页/共27页Fluid Mosaic Model FluidFluid:there is lateral motion of components in the membrane;proteins,for example,“float”in the membrane and can move along its plane MosaicMosaic:components in the membrane exist side-by-side as separate entitiesthe structure is that of a

19、lipid bilayer with proteins,glycolipids,and steroids such as cholesterol embedded in itno complexes,as for example,lipid-protein complexes,are formed第25页/共27页Membrane TransportPassive transportPassive transportdriven by a concentration gradient simple diffusionsimple diffusion:a molecule or ion move

20、s through an opening created by a channel protein facilitated diffusionfacilitated diffusion:a molecule or ion is carried across a membrane by a carrier protein Active transport Active transport a substance is moved against a concentration gradient primary active transport:primary active transport:transport is linked to the hydrolysis of ATP or other high-energy molecule;for example,the Na+/K+ion pump(Figures 7.24 and 7.25)secondary active transport:secondary active transport:driven by H+gradient第26页/共27页感谢您的观看！第27页/共27页