Digestion and Absorption

• Digestion


  The hydrolysis of large, insoluble molecules into smaller molecules that can be absorbed across cell membranes
• Enzymes involved in carbohydrate digestion

  • Amylase in mouth
  • Maltase, sucrase, lactase in membrane of small intestine
• Carbohydrate digestion


  1. Amylase → starch into smaller polysaccharides

  2. Maltase → maltose into 2 x glucose

  3. Sucrase → sucrose into glucose and fructose

  4. Lactase → lactose into glucose and galactose
• Where lipids are digested


  The small intestine
• Lipid digestion


  1. They must be emulsified by bile salts produced by the liver. This breaks down large fat molecules into smaller, soluble molecules called micelles, increasing surface area.

  2. Lipase hydrolyses the ester bond between the monoglycerides and fatty acids
• Enzymes involved in protein digestion

  • Endopeptidases= break between specific amino acids in the middle of a polypeptide
  • Exopeptidases= break between specific amino acids at the end of a polypeptide
  • Dipeptidases= break dipeptides into amino acids
• Co-transport


  How certain molecules are absorbed into the ileum despite a negative concentration gradient
• Molecules that require co-transport

  • Amino acids
  • Monosaccharides
• How sodium ions are involved in co-transport

  Sodium ions (Na+) are actively transported out of the cell into the lumen, creating a diffusion gradient. Nutrients are then taken up into the cells along with Na+ ions
• Fatty acids and monoglycerides do not require co-transport