Lipid triacylglycerols

Fat absorbed from the diet and lipids synthesized by the liver and adipose tissue must be transported between the various tissues and organs for utilization and storage. Since lipids are insoluble in water, the problem of how to transport them in the aqueous blood plasma is solved by associating nonpolar lipids (triacylglycerol and cholesteryl esters) with amphipathic hpids (phospholipids and cholesterol) and proteins to make water-miscible hpoproteins. 

Hydrophobic lipids (triacylglycerols and cholesteryl esters) are virtually completely insoluble in water they are solubilized for transport in plasma by incorporation into lipoproteins. Lipoproteins are spherical complexes containing triacylglycerol (triglyceride) and cholesteryl ester surrounded by a layer containing phospholipids, unesterified cholesterol, and specific apolipoproteins. 

Understanding the geometry of C-C double bonds provides an insight into the properties of triacylglycerols, the most abundant lipids. Triacylglycerols contain three ester groups. 

Fig. 6. Model for delivery of dietary lipid from the midgut to the fat body. Dietary lipid (triacylglycerol, TG) is hydrolyzed to fatty acid (FA) in the lumen of the midgut, ahsorhed into midgut epithelial cells, and used to synthesize diacylglycerol (DG). The DG is picked up by lipophorin via a mechanism that does not involve internalizauon of the lipophorin. Two cases are shown. In one case, newly synthesized (nascent) lipophorin (nLp), which is secreted from the fat body, picks up DG from the midgut and is converted to a DG-loaded HDLp. The DG-loaded HDLp then moves to the fat body, where it delivers the DG without internalization and is converted to a DG-unloaded HDLp. In the second case, the DG-unloaded HDLp travels to the midgut, where it picks up DG and is converted to a DG-loaded HDLp.

Very-low-density lipoproteins (VLDL) are large particles (diameter 300-900 A, density range 0.95-1.006 g/ml, pre-]8 electrophoretic mobility, Fig. 1) in which triacylglycerols predominate. VLDL contain 8-10% protein (predominantly apo-B and apo-E, see Fig. 2) and 90-92% lipid (triacylglycerols 56%, phospholipids 19-21%, cholesterol and cholesterol esters 17% [6]). VLDL are synthesized in the... 

The general structural organization is similar for all the lipoprotein classes the apolipoproteins and amphipathic lipids (mostly phospholipids (PL) and unesterified cholesterol) form a 20-A-thick shell on the surface of spherical particles. This shell encloses the core of neutral lipids (triacylglycerols, cholesteryl esters (CE), and small amounts of unesterified cholesterol and other dissolved lipids, e.g., lipid-soluble vitamins). The main protein components are characteristic of each lipoprotein class they are indicated in Fig. 1, and will be described in detail in Section 3 of this chapter. 

In the second part of this experiment you will characterize the purified lipids (triacylglycerols) isolated from nutmeg. The fatty acids m the triacylglycerols are released by saponification and their identities determined by gas chromatography. Alternatively, students may be provided various fat and oil samples for analysis. For example, the fatty acid content of triacyl-... 

Influence of Dietary Conjugated Linoleic Acid (CLA 2.5%) on the Fatty Acid Composition of Total Lipids, Triacylglycerols, Phosphatidylcholine (PC), and Phosphatidylethanolamine (PE)... 

Fluid Species or tissue Sterols Lipid Triacylglycerols % total lipids Phospholipids Reference... 

Aursand, M., Jorgensen, L. and Grasdalen, H. (1995) Positional distribution of co-3 fatty acids in marine lipid triacylglycerols by high-resolution C-nuclear Magnetic resonance spectroscopy. J. Am. Oil Chem. Soc., 72 (3), 293-7. 

Bovine milk fat is made up of 97-98 (wt% of total lipids) triacylglycerols accompanied by much smaller amounts of diacylglycerols (0.36%) and monoacylglyc-erols (0.03%), free cholesterol (0.31%), trace amounts of cholesteryl esters, phospholipids (0.60%), and minor amounts of free fatty acids. For reviews of the composition of bovine milk lipids, the reader is referred to Christie (4) and Jensen and Clarke (5). More than 400 fatty acids have been identified in milk fat, although it is generally accepted that 15 major and 12 minor fatty acids dominate the fatty acid spectrum. The major fatty acids found in milk are long chain (Cj. , myristic Ci6-o. palmitic Cjg., stearic Cjg.j, oleic) and the minor fatty acids are short chain... 

The fatty acid composition of major lipid classes showed a small, but significant (P<0.05), difference between total lipids, triacylglycerols and phospholipids of sesame oil after microwave heating (Yoshida et al, 1995). Yoshida et al (1995) have determined the optimum exposure time as 16 min for heat processing of sesame seeds by microwaving. 

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