Lesson 2 Science

• Enzymes


  Protein substances that can initiate or speed up chemical reactions
• Enzymes


  • Optimum temperature for enzymes to work well in the body is between 35°C to 40°C
  • Specificity of enzymes is similar to how a key fits into a lock
• Substrates


  Substances that are acted upon by enzymes
• Enzymes act on specific substrates
• Enzyme specificity


  Emil Fischer's "lock and key model"
• Digestive enzymes


  Responsible for changing food into simple molecules that cells can absorb and utilize
• Groups of digestive enzymes


  • Carbohydrases
  • Proteinases
  • Lipases
• Chemical digestion of carbohydrates


  1. Begins in the mouth with salivary amylase (ptyalin) breaking down carbohydrates into disaccharides

  2. Continues in the stomach where the bolus is changed into chyme by mechanical digestion

  3. In the small intestine, pancreatic amylopsin further breaks down carbohydrates into disaccharides

  4. Intestinal enzymes (maltase, lactase, sucrase) break down disaccharides into monosaccharides (glucose, fructose, galactose)
• Chemical digestion of protein


  1. Begins in the stomach with pepsin breaking down protein into small polypeptides

  2. Continues in the small intestine with trypsin further breaking down polypeptides into dipeptides

  3. Intestinal enzymes (aminopeptidases, erepsin) break down polypeptides and dipeptides into amino acids
• Chemical digestion of fats


  1. Begins and ends in the small intestine

  2. Pancreatic enzyme steapsin breaks down fats into fatty acids and glycerol

  3. Intestinal enzyme, steapsin, further breaks down fats into fatty acids and glycerol
• The intestinal glands secrete the enzyme intestinal steapsin and will act on fats, changing them to fatty acids and glycerol


  intestinal glands, fatty acid, glycerol