Which one of the following is not associated with carbohydrate digestion, absorption, or both?
Enterokinase is an intestinal enzyme that activates trypsinogen as it enters the small intestine from the pancreas. Enterokinase is secreted into the lumen by mucosa cells, but much of it adheres to the enterocyte membrane. Once activated, trypsin can fuher activate itself as well as other inactive proteases. Amylase is secreted in active form and does not depend on enterokinase to be effective.Amylase is found in saliva and pancreatic juice.Starch is ingested in two forms, amylose and amylopectin. Amylase hydrolyzes amylose to maltose or maltotriose. Amylopectin contains -1,6 branch points, which cannot be digested by amylase. In this case, a limit dextrins are produced; they are polysaccharide fragments of variable size, each containing an -1,6 linkage. The brush-border enzyme -dextrinase completes the digestion of a-limit dextrins to single glucose units.Sucrase is a brush-border enzyme that hydrolyzes sucrose to glucose and fructose. These monosaccharides are subsequently absorbed by the enterocyte.The absorption of glucose and galactose is secondary active transpo. The absorption is sodium dependent. A carrier molecule in the mucosal membrane binds two sodium molecules for every glucose or galactose molecule; these two monosaccharides share the same transpo protein. Basolateral membrane sodium-potassium ATPase pumps keep the enterocyte intracellular concentration of sodium low. This situation provides a concentration gradient that ors the movement of sodium from the lumen into the enterocyte. Sodium moving down its concentration gradient can bring glucose or galactose into the enterocyte, even against a concentration gradient.
Amylase
Sucrase
Secondary active transpo
Enterokinase
G.I.T