2 MetabolismRecall: metabolism = all chemical reactions occurring in the body.Reactants = substances that “enter” a chemical reactionProducts = substances that are formed by a chemical reactionMetabolic pathways = specific series of reactions in the bodyBegin with specific reactants and make specific produts.Occur over many steps.Each step is triggered by a catalyst called an enzyme.
3 Metabolism cont’d Enzymes Protein molecules which function as catalysts to speed up rate of chemical reactionsIn a reaction using an enzyme, the “reactant” is called a substrate.
4 Digestive Enzymes - Overview Much of digestion relies on the use of specific digestive enzymes.Many cause hydrolytic reactions to occur.Substrate is broken down by a reaction with water.Large nutrients get broken into smaller molecules.Digestive enzymes need an optimal pH to work properly.Maintains shape of the enzyme.
5 Major Digestive enzymes Salivary amylaseCatalyzes the reaction: starch + H2O maltoseStarch is broken down into a smaller sugar – maltose.Maltose is made up of two glucoseOccurs in the mouth
6 Major Digestive Enzymes cont’d PepsinCatalyzes the reaction: protein + H2O peptidesOnly active when pH < 2Occurs in the stomach in presence of HCl (strong acid).
7 Major Digestive enzymes cont’d. Pancreatic amylaseCatalyzes the reaction: starch + H2O maltoseOccurs in duodenum (part of the small intestine)pH must be a little basic (over 7).Completes digestion of starches to disaccharidesDisaccharides are molecules made up of 2 sugar molecules.
9 Major Digestive enzymes cont’d. TrypsinCatalyzes the reaction: protein + H2O peptidesOccurs in duodenumProduced by pancreas as trypsinogen – an inactive form (switched off).Activated (switched on) in duodenum by another enzyme called enterokinase.
10 Major Digestive Enzymes cont’d LipaseCatalyzes the reaction: fats + H2O glycerol + 3 fatty acidsOccurs in duodenum
11 Major Digestive enzymes cont’d. PeptidasesCatalyze reaction: peptides + H2O amino acidsOccurs in small intestineMaltaseCatalyzes reaction: maltose + H2O 2 GlucoseEach disaccharide has its own enzyme (like maltase)Examples include lactase and sucraseLactase = enzyme that breaks down lactose; sucrase = enzyme that breaks down sucrose.
13 Digestive Enzymes – Conditions Required Environmental conditions must be optimumChanges to conditions harm the enzymes.Conditions include:Warm temperatureMost function well at normal body temperatureExtreme heat causes irreversible shape change – denaturing.Correct pHEach enzyme has its own optimal pHMost function at near neutral pH (7).Others prefer acidic (lower pH) or basic (higher pH) conditions.