Digestion and absorption

• Define digestion


  The hydrolysis of large, insoluble molecules into smaller molecules that can be absorbed across cell membranes
• Which enzymes are involved in carbohydrate digestion and where are they found

  ~Amylase in mouth

  ~Maltase, sucrase, lactase in membrane of small intestine
• What are the substrates and products of the carbohydrate digestive enzymes

  ~Amylase = starch into smaller polysaccharides

  ~Maltase = maltose into 2x glucose

  ~Sucrase = sucrose into glucose and fructose

  ~Lactase = lactose into glucose and galactose
• Where are lipids digested

  The small intestine
• What needs to happen before lipids can be digested

  ~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
• How are lipids digested

  Lipase hydrolyses the ester bond between the monoglycerides and fatty acids
• Which enzymes are involved in protein digestion and what are there roles

  ~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
• How are certain molecules absorbed into the ileum despite a negative concentration gradient

  Through co-transport
• Which molecules require co-transport

  Amino acids and monosaccharides
• Explain how sodium ions are involved in co-transport

  ~Sodium ions are actively transported out of the cell into the lumen, creating a diffusion gradient

  ~Nutrients are then taken up into cells along with Na+ ions
• Why do fatty acids and monoglycerides not require co-transport

  The molecules are nonpolar, meaning they can easily diffuse across the membrane of the epithelial cells