Triacylglycerols

Abstract

Triacylglycerols are an important source of energy in the human diet, and when not immediately required for this purpose may be stored in the body in adipocytes.They are transported in thebloodstream as chylomicrons and very low‐density lipoproteins and stores are continually being broken down and resynthesized.

Keywords: triacylglycerol; lipoprotein; lipolysis; chylomicron; fatty acid

Figure 1.

Formation of a triglyceride molecule.

Figure 2.

Names and structures of some common fatty acids.

Figure 3.

Digestion and absorption of dietary lipids. (1) Dietary lipid leaves the stomach and enters the upper region of the small intestine where bile acids, released from the gallbladder,surround and coat droplets of fat to form emulsion particles. The emulsion particles provide the surface area for the pancreatic enzymes to degrade the dietary lipids. (2) Phospholipase A2 (PLA2) breaks down each phospholipid (PL)into a free fatty acid (FFA) and a lysophospholipid (LPL). (3) Pancreatic lipase (PLps) converts triglyceride (TG) into a monoglyceride (MG) and two free fatty acids. (4) Cholesterol esterase (CEtrs) splits cholesterol ester (CE) into free cholesterol and a free fatty acid. (5) The products of lipid digestion coalesce with bile acids into mixed micelles. (6) The mixed micelles move close to the mucosal cell surface, where the lipids diffuse down a concentration gradient into the mucosal cells. (7) Bile acids are not absorbed. (8) Short‐ and medium‐chain fatty acids move immediately into the portal circulation where they are transported in the blood bound to albumin. (9) To maintain the concentration gradient necessary for lipid diffusion, the breakdown products of lipid digestion are resynthesized into their parent lipids. (10) The lipids are combined with apolipoproteins, synthesized in the mucosal cells, to form chylomicrons. (11) Chylomicrons leave the mucosal cell via the lymphatic vessels.

Figure 4.

Structure of a plasma lipoprotein.

Figure 5.

Desaturation and elongation of polyunsaturated fatty acids.

Figure 6.

Synthesis and degradation of triacylglycerol.

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Further Reading

Berdanier CD (2000) Advanced Nutrition: Macronutrients. Boca Raton, FL: CRC Press.

Mann J and Skeaff M (1998) Lipids. In: Mann J and Truswell AS (eds) Essentials of Human Nutrition, pp. 29–50. Oxford: Oxford University Press

Murray RK, Granner DK, Mayes PA and Rodwell VW (1993) Harper’s Biochemistry, 23rd edn. Norwalk, CT: Appleton and Lange.

Shils ME, Olson JA, Shike M and Ross AC (eds) (1999) Modern Nutrition in Health and Disease. Baltimore: Williams and Wilkins..

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How to Cite close
Mann, Jim, and Skeaff, Murray(Apr 2001) Triacylglycerols. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1038/npg.els.0000720]