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
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.