Nutrition and Metabolism
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.
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.
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.
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
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).
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.
Disaccharide examples
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.
Major Digestive Enzymes cont’d
• Lipase– Catalyzes the
reaction: fats + H2O glycerol + 3 fatty acids
– Occurs in duodenum
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.
Major Digestive enzymes cont’d.
• Table 14.3
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.