ProteinsLipoproteinsLipoproteins contain both protein and lipid Primary source of circulating lipidsHeadgroupsofcholesteroland Protein component makes them solublephospholipids Proteins target particles to cell surface Modulate enzymes that act on lipids
Lipoproteins Lipoproteins contain both protein and lipid Primary source of circulating lipids Protein component makes them soluble Proteins target particles to cell surface Modulate enzymes that act on lipids
Lipoproteins. When most lipids circulate in the body, they do so in the form oflipoprotein complexes. Simple, unesterified fatty acids are merelybound to serum albumin in blood plasma, but phospholipids,triacylglycerols, cholesterol, and cholesterol esters are all transported inthe form of lipoproteins.: At various sites in the body, lipoproteins interact with specific receptorsand enzymesthattransfer or modifytheirlipid cargoes.? It is now customary to classify lipoproteins according to their densities
Lipoproteins • When most lipids circulate in the body, they do so in the form of lipoprotein complexes. Simple, unesterified fatty acids are merely bound to serum albumin in blood plasma, but phospholipids, triacylglycerols, cholesterol, and cholesterol esters are all transported in the form of lipoproteins. • At various sites in the body, lipoproteins interact with specific receptors and enzymes that transfer or modify their lipid cargoes. • It is now customary to classify lipoproteins according to their densities
Lipids transported via lipoproteinsCharacteristics of lipoproteins(as%proteinincreases,densityincreases)%Cholesterol%%DiameterDensityandCholesteryl(A)Lipoprotein(g·cm-")ProteinTriacylglycerolEster12Chylomicrons1000-5000<0.9585-904-8VLDL0.951.00651050651525300-800IDL250-3501.006-1.01910-2020-3040-45LDL20-25715180-2501.019-1.06345-50HDL40-55310152050-1201.063-1.210Becausemostproteinshavedensitiesofabout1.3to1.4g/mL,andlipid aggregates usually possess densities of about 0.8 g/mL, the moreprotein and the less lipid in a complex, the denser the lipoprotein
Because most proteins have densities of about 1.3 to 1.4 g/mL, and lipid aggregates usually possess densities of about 0.8 g/mL, the more protein and the less lipid in a complex, the denser the lipoprotein. Lipids transported via lipoproteins Characteristics of lipoproteins (as % protein increases, density increases)
ApolipoproteinsLipoproteinsPhospholipidsCholesterolTriacylglycerolsandcholesterylestersTypes oflipoproteinsChylomicrons（乳糜微粒）Dietary lipids that travel from intestine to other tissuesLarge and mostly lipid (1-2% protein) Transport triacylglycerols to adipose tissue and cholesterol to liver
（乳糜微粒） Lipoproteins Types of lipoproteins Chylomicrons • Dietary lipids that travel from intestine to other tissues • Large and mostly lipid (1-2% protein) • Transport triacylglycerols to adipose tissue and cholesterol to liver Apolipoproteins Triacylglycerols and cholesteryl esters Phospholipids Cholesterol
This imageisbased onsmall angleneutronscatteringofHDLparticlesThree copies of apolipoproteinA1(orange)wraparound a core containing phospholipids,cholesterol,and cholesteryl esters.The proteins help target the particle to cellsurfacesand modulatethe activitiesofenzymesthatactonthecomponentlipids.The various types of lipoproteins differ in size,lipidcomposition,proteincomposition,anddensity
This image is based on small angle neutron scattering of HDL particles. Three copies of apolipoprotein A1 (orange) wrap around a core containing phospholipids, cholesterol, and cholesteryl esters. The proteins help target the particle to cell surfaces and modulate the activities of enzymes that act on the component lipids. The various types of lipoproteins differ in size, lipid composition, protein composition, and density