Nutrition and Metabolism

1. Nutrition and Metabolism

2. Metabolism • Recall: metabolism = all chemical reactions occurring in the body. • Reactants = substances that “enter” a chemical reaction • Products = substances that are formed by a chemical reaction • Metabolic pathways = specific series of reactions in the body • Begin 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 reactions • In 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 amylase • Catalyzes the reaction: starch + H2O  maltose • Starch is broken down into a smaller sugar – maltose. • Maltose is made up of two glucose • Occurs in the mouth

6. Major Digestive Enzymes cont’d • Pepsin • Catalyzes the reaction: protein + H2O  peptides • Only active when pH < 2 • Occurs in the stomach in presence of HCl (strong acid).

7. Major Digestive enzymes cont’d. • Pancreatic amylase • Catalyzes the reaction: starch + H2O  maltose • Occurs in duodenum (part of the small intestine) • pH must be a little basic (over 7). • Completes digestion of starches to disaccharides • Disaccharides are molecules made up of 2 sugar molecules.

8. Disaccharide examples

9. Major Digestive enzymes cont’d. • Trypsin • Catalyzes the reaction: protein + H2O  peptides • Occurs in duodenum • Produced 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 • Lipase • Catalyzes the reaction: fats + H2O  glycerol + 3 fatty acids • Occurs in duodenum

11. Major Digestive enzymes cont’d. • Peptidases • Catalyze reaction: peptides + H2O  amino acids • Occurs in small intestine • Maltase • Catalyzes reaction: maltose + H2O  2 Glucose • Occurs in small intestine • Each disaccharide has its own enzyme (like maltase) • Examples include lactase and sucrase • Lactase = enzyme that breaks down lactose; sucrase = enzyme that breaks down sucrose.

12. Major Digestive enzymes cont’d. • Table 14.3

13. Digestive Enzymes – Conditions Required • Environmental conditions must be optimum • Changes to conditions harm the enzymes. • Conditions include: • Warm temperature • Most function well at normal body temperature • Extreme heat causes irreversible shape change – denaturing. • Correct pH • Each enzyme has its own optimal pH • Most function at near neutral pH (7). • Others prefer acidic (lower pH) or basic (higher pH) conditions.