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LABORATORY - CHEMICAL AND PHYSICAL PROCESSES OF DIGESTION: WET LAB (Based on Marieb, 2005) Chemical Digestion of Foodstuffs: Enzymatic Action Because nutrients can be absorbed only when broken down to their monomers, food digestion is a prerequisite to absorption. Enzymes are large protein molecules produced by body cells. They are biological catalysts, meaning they increase the rate of a chemical reaction without themselves becoming part of the product. The digestive enzymes are hydrolytic enzymes, or hydrolases. Their substrates, or the molecules on which they act, are organic food molecules which they break down by adding water to the molecular bonds, thus cleaving the bonds between the subunits or monomers. The various hydrolytic enzymes are highly specific in their action. Each enzyme hydrolyzes only one or a small group of substrate molecules, and specific environmental conditions are necessary for it to function optimally. Since digestive enzymes actually function outside the body cells in the digestive tract, their hydrolytic activity can also be studied in a test tube. Such an in vitro study provides a convenient laboratory environment for investigating the effect of such variations on enzymatic activity. Table 1 shows the progressive digestion of proteins, fats, and carbohydrates. It indicates specific enzymes involved, their site of formation, and their site of action. Acquaint yourself with the table before beginning this experiment, and refer to it as necessary during the laboratory session. Objectives • To list the digestive system enzymes involved in the digestion of proteins, fats, and carbohydrates; to state their site of origin; and to summarize the environmental conditions promoting their optimal functioning. • To recognize the variation between different types of enzyme assays. • To name the end products of protein, fat, and carbohydrate digestion. • To perform the appropriate chemical tests to determine if digestion of a particular foodstuff has occurred. • To cite the function(s) of bile in the digestive process. • To discuss the possible role of temperature and pH in the regulation of enzyme activity, • To define enzyme, catalyst, control, substrate, and hydrolase. • To explain why swallowing is both a voluntary and a reflex activity. • To discuss the role of the tongue, larynx, and gastroesophageal sphincter in swallowing. • To compare and contrast segmentation and peristalsis as mechanisms of propulsion. 1

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