Dietary triglyceride is a major source of nutrient for the human body. It is digested mostly in the intestinal lumen by pancreatic lipase to release:
Ans. D. 2-Monoglyceride and fatty acidsa. Pancreatic lipase hydrolyzes triglyceride to form 2-monoglyceride and two fatty acids. The hydrolysis of phosphatidylcholine, not triglyceride, results in the formation of lysophosphatidylcholines. Although diglyceride is an intermediate in the hydrolysis of triglyceride by pancreatic lipase, the hydrolysis continues until 2-monoglyceride and fatty acids are formed. Pancreatic lipase does not hydrolyze triglyceride totally to form glycerol and fatty acids.b. Most fat digestion therefore begins in the duodenum, pancreatic lipase being one of the most important enzymes involved. This enzyme hydrolyzes the 1- and 3-bonds of the triglycerides (triacylglycerors) with relative ease but acts on the 2-bonds at a very low rate, so the principal products of its action are free fatty acids and 2-monoglycerides (2- monoacylglycerols). It acts on fats that have been emulsified (see below). Its activity is facilitated when an amphipathic helix that covers the active site like a lid is bent back.c. Colipase, a protein with a molecular weight of about 11,000, is also secreted in the pancreatic juice, and when this molecule binds to the -COOH-terminal domain of the pancreatic lipase, opening of the lid is facilitated. Colipase is secreted in an inactive proform and is activated in the intestinal lumen by trypsin. Another pancreatic lipase that is activated by bile salts has been characterized. This 100,000-kDa cholesterol esterase represents about 4% of the total protein in pancreatic juice. In adults, pancreatic lipase is 10-60 times more active, but unlike pancreatic lipase, this bile salt-activated lipase catalyzes the hydrolysis of cholesterol esters, esters of fat-soluble vitamins, and phospholipids, as well as triglycerides. A very similar enzyme is found in human milk.d. Fats are relatively insoluble, which limits their ability to cross the unstirred layer and reach the surface of the mucosal cells. However, they are finely emulsified in the small intestine by the detergent action of bile salts, lecithin, and monoglyceride. When the concentration of bile salts in the intestine is high, as it is after contraction of the gallbladder, lipids and bile salts interact spontaneously to form micelles. These cylindrical aggregates, take up lipids, and although their lipid concentration varies, they generally contain fatty acids, monoglyceride, and cholesterol in their hydrophobic centers. Micellar formation further solubilizes the lipids and provides a mechanism for their transport to the enterocytes. Thus, the micelles move down their concentration gradient through the unstirred layer to the brush border of the mucosal cells. The lipids diffuse out of the micelles, and a saturated aqueous solution of the lipids is maintained in contact with the brush border of the mucosal cells
Lysophosphatidylcholines and fatty acids
Glycerol and fatty acids
Diglyceride and fatty acids
2-Monoglyceride and fatty acids
G.I.T.