BC1502 Introduction to Cell and Molecular BiologyMacromolecules
Nutrition & biochemistryLecture 5b
James A Martiney, Ph.D.
Enzymatic Digestion of Nutrients
Figure 47-9 p1053
Figure 47.9 Enzymatic digestion of carbohydrates, proteins, fats, and nucleic acids in the human digestive system.
Absorption and digestion of disaccharides and small peptides
Figure 47-14 p1057Polysaccharides and disaccharidesDisaccharidasesBrush-border cells of intestinal mucosaAmino acidsMonosaccharidesTo extracellular fluid and blood
Small peptidesLumenof smallintestineAminopeptidases
Figure 47.14 Absorption and digestion of disaccharides and small peptides by the brush-border cells of the small intestinal mucosa.
Figure 47-15 p1058Brush-border cells of intestinal mucosaLumenof smallintestine
InterstitialfluidEndoplasmicreticulumMonoglyceridesTriglyceridesChylomicronsChylomicrons exit the cell byexocytosis and enter lymph vessels.ChylomicronFatty acidsMicellesBile saltsMonoglyceridesFatty acidsAbsorption of fat-soluble products of digestionby intestinal mucosa cellsLipoproteincoatAggregatedtriglyceridesAggregate and coated with lipoprotein
Figure 47.15 Absorption of monoglycerides and fatty acids, the products of fat digestion in the luman of the small intestine, by the brush-border cells of the small intestinal mucosa.
Monoglycerides and fatty acids associate with bile salts to form water-soluble microdroplets called micelles. Micelles carry their contents to the microvillar membranes of the brush-border epithelial cells where the monoglycerides and fatty acids enter the cells by passive diffusion through the plasma membranes. Within the cells, triglycerides are resynthesized from the monoglycerides and fatty acids. The triglycerides aggregate and are coated with lipoproteins from the endoplasmic reticulum to form chylomicrons, which leave the cell by exocytosis and enter the lymphatic system.