Digestion and Absorption of Carbohydrates PDF

Digestion and adsorption of carbohydrates Classification of carbohydrates Content of carbohydrates in food  Digestion of carbohydrates Salivary amylase, is a major component of human saliva that initiates carbohydrate digestion in the mouth. Salivary amylas...

Digestion and adsorption of carbohydrates Classification of carbohydrates Content of carbohydrates in food  Digestion of carbohydrates Salivary amylase, is a major component of human saliva that initiates carbohydrate digestion in the mouth. Salivary amylase enzyme breaks down starch into maltose a disaccharide of glucose, which is sometimes further broken down to glucose.  Digestion of carbohydrates Further digestion of carbohydrates by pancreatic enzymes occurs in the small intestine. When the acidic stomach contents reach the small intestine, they are neutralized by bicarbonate secreted by the pancreas, and pancreatic α-amylase continues the process of starch digestion.  Hydrolysis of starch by pancreatic alfa- amylase сн2он сн2он o o он он о о о он он n сн2он n Н 2О o n он он он он glucose Pancreatic α-amylase continues to hydrolyze the starches and glycogen, forming the disaccharide maltose, and oligosaccharides. These oligosaccharides, called limit dextrins (4-9) glucosyl units  Glycosidases The dietary disaccharides lactose and sucrose, as well as the products of starch digestion, are converted to monosaccharides by glycosidases attached to the membrane in the brush border of absorptive cells. The different glycosidase activities are found in four glycoproteins: maltase-glucoamylase, sucrase–isomaltase complex, trehalase, and lactase  Maltase-glucoamylase Maltase-glucoamylase is an alpha-glucosidase digestive enzyme. It consists of two subunits with differing substrate specificity. Its N-terminal catalytic domain has the highest activity against maltose, while the C-terminal domain has a broader substrate specificity and activity against glucose oligomers.  Sucrase–Isomaltase Complex Sucrase-isomaltase is a single gene product that has two active sites. The sucrase site splits sucrose into glucose and fructose. These two monosaccharides can then be absorbed by brush border transporters. The isomaltase active site cleaves maltose at its α(1,4) bond and it cleaves limit dextrins at their α(1,6) bond. СН2ОН СН 2ОН О О ОН ОН ОН ОН ОН Н 2О ОН ОН О glucose СН2ОН СН 2ОН О О ОН он он СН2ОН он он СН2ОН fructose  Trehalase Trehalase is a glycoside hydrolase, produced by cells in the brush border, which catalyzes the conversion of trehalose (naturally found in mushrooms and algae) into glucose.  Lactase Lactase is an enzyme present in the gut that is responsible for breaking down complex lactose sugars into simpler sugars such as glucose and galactose which can then be utilized for energy and bodily functions. Lactose intolerance Lactose intolerance refers to a condition of pain, nausea, and flatulence after the ingestion of foods containing lactose, most notably dairy products. Lactose intolerance is most often caused by low levels of lactase. Lactase activity increases in the human from about 6 to 8 weeks of gestation. It remains high for about 1 month after birth and then begins to decline. For most of the world’s population, lactase activity decreases to adult levels at approximately 5 to 7 years of age. Adult levels are