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Chemical Digestion and Enzymes The major nutrients taken in by the body through eating are carbohydrates, proteins, fats and nucleic acids. These large macromolecules need to be broken down by the digestive system into their simpler building blocks. In order to breakdown these nutrient they under go a chemical reaction called HYDROLYSIS. Hydrolysis is the use of water to break the bonds between the monomers (building blocks) of the macromolecules. Hydrolysis is a slow reaction and needs to be sped up. The body solves this problem by making a biological catalyst called enzymes. Enzymes are special proteins produced by the cell. Enzymes break the bonds between monomers at very specific locations (linkages). Enzymes often require special conditions in order to act i) ii) iii) iv) some work best in an acidic environment (i.e. pepsin in the stomach) other work in a neutral or alkaline (basic) environment (i.e.. the digestive enzymes in the small intestine) enzymes are affected by temperature changes (i.e. higher temperatures will denature the enzyme so that it is no longer functional) in order for the enzyme to function properly it may require the presence of metallic ions (i.e. cobalt and magnesium), vitamins, or coenzymes in order to function properly. There are three groupings of enzymes that are formed by secretory cells and then secreted into the digestive tract. Macromolecule carbohydrates proteins fats Enzyme Carbohydrases Proteases Lipases Monomers monosaccharides (glucose, galactose, fructose) amino acids glycerol + 3 fatty acids Digestive Enzymes Most of the digestive enzyme names start with the name of the substrate they react on and have the ending "ase" added. Example: maltose is broken down by an enzyme called maltase. Some enzymes still use their older names such as pepsin. __________________________________________________________________________________________ 478172156 Page 1 of 5 A Summary of Chemical Digestion In humans and other mammals, chemical digestion begins in Salivary glands release the enzyme called salivary amylase, Amylase breaks down starch into smaller disaccharide sugar molecules stomach gastric juice secreted by the stomach contains hydrochloric acid and the enzyme, pepsin. Pepsin begins the breakdown of protein in the stomach Pepsin functions well within a pH range of 1 to 2. duodenum is 25 cm long secretes enzymes from its lining, the pancreas and liver both empty their enzymes into the duodenum to complete the process of digestion. Pancreatic juice is alkaline and thus neutralizes the acidity of partially digested food coming from the stomach, stopping any further action of pepsin produces no enzymes water is absorbed from indigestible material through its walls anaerobic bacteria living there, digest some of this material, and some of it is absorbed for use by the body synthesize some B vitamins and Vitamin K which is then used by the body. The total digestion of a large meal takes about 24-33 h mouth pancreas Large intestine The Regulation of Digestive Secretions The secretion of digestive enzymes is regulated by both nerves and hormones. A hormone is a chemical regulator that is secreted in one part of the body and transported by the bloodstream to another part, where it causes a response. Examples a) Secretion of Gastric Juices Nerve impulse stimulates the lower part of the stomach to produce the hormone gastrin Gasterin enters the circulatory system and is carried back to the upper part of the stomach Gasterin then stimulates the digestive glands lining the walls of the upper part of the stomach to secrete mucin pepsin, hydrochloric acid, lipases. b) Neutralization of Chyme Chyme entering the duodenum stimulates the glands of the duodenum to secrete the hormone secretin into the bloodstream Secretin stimulates the duct cells of the pancreas to release an alkaline fluid containing sodium carbonate and sodium bicarbonate into the duodenum which changes the pH from 2 to 8 __________________________________________________________________________________________ 478172156 Page 2 of 5 c) The hormone secretin and cholecystokinin (CCK) are secreted by the duodenum and stimulates the pancreas to release its digestive enzymes into the duodenum. These enzymes also stimulate the gall bladder to secrete bile salt. Enzymes of the Human Digestive System Place where enzyme acts Substrate Enzyme mouth starch, glycogen salivary amylase stomach protein fats fats peptides peptides peptides starch small intestine ribonucleic acid deoxyribonucleic acid peptides tripeptides maltose sucrose lactose pepsin lipase pancreatic lipase trypsin chymotrypsin carboxypeptidase pancreatic amylase ribonuclease deoxyribonuclease aminopeptidase tripeptidase maltase sucrase lactase Products Origin of Enzyme maltose salivary glands peptides stomach glands glycerol + 3 fatty acids glycerol + 3 fatty acids simpler peptides simpler peptides simpler peptides pancreas maltose ribonucleotides deoxyribonucleotides simpler peptides dipeptide + amino acid glands in the walls of the small intestine glucose + glucose glucose + fructose intestinal glands glucose + galactose __________________________________________________________________________________________ 478172156 Page 3 of 5 The Roles of Related Organs Three other organs associated with the digestive tract are the liver, gall bladder, and pancreas. These organs play vital roles in the digestive process. The Liver The liver is the largest organ in the body and has been identified as having over 500 different functions that are essential to the body's general good health. produces bile salts from cholesterol which is released into the small intestine to emulsify fat globules (break up ) to allow lipase to chemical break the fat up into glycerol and fatty acids breaks down old red blood corpuscles, and hemoglobin the decomposed hemoglobin molecules are used to make bile salts. the liver collects from the bloodstream chemicals that are in excess of the amount needed by the body at any given time. The liver converts and stores all monosaccharides (except glucose), into glycogen The liver will convert the stored glycogen back into glucose when the glucose level in the bloodstream become low The liver also stores fat-soluble vitamins A, D, E, and K the liver works to detoxify various poisons ingested with food and drink in addition to those produced in the intestines. The liver is highly evolved organ that performs a wide range of important, specialized functions for the body. The Gall Bladder The gall bladder serves as the storage warehouse for bile produced in the liver. bile contains a number of chemicals that include cholesterol bile salts are used in fat digestion bile salts are reabsorbed by the small intestine and is carried back to the liver to be recycled back into bile The Pancreas The pancreas is the source of several enzymes that act on carbohydrates, fats, and peptides (smaller segments of proteins) produces and releases a basic solution that changes the pH of chyme (from a strongly acid mixture to a weakly basic one) after it enters the duodenum. __________________________________________________________________________________________ 478172156 Page 4 of 5