Digestion

• Digestion

  Hydrolysis of large insoluble molecules into small soluble molecules so that they can be absorbed across cell membranes and into the bloodstream
• Proteins hydrolyse into ...

  amino acids
• carbohydrates hydrolyse into ...

  simple sugars
• lipids hydrolyse into ...

  fatty acids and glycerol
• carbohydrates are digested by ...

  amylase and membrane bound disaccharidases
• protease enzymes

  endopeptidase

  exopeptidase

  dipeptidase
• Where does endopeptidase hydrolyse peptide bonds

  between amino acids in the middle of a polypeptide to form dipeptides
• Where is endopeptidase and exopeptidase found?

  In stomach and small intestine
• Where does exopeptidase hydrolyse peptide bonds?

  Between amino acids at the end of a polypeptide to form dipeptides
• Where does dipeptidase hydrolyse peptide bonds?

  Between dipeptides to form amino acids
• Process of emulsification of lipids by bile salts and hydrolysis of lipids

  bile containing bile salts released from gallbladder through bile ducts into the duodenum emulsifies lipids into smaller lipid droplets with an increased SA to enable faster hydrolysis by lipase
• Micelles

  vesicles containing the products of lipids digestion which allow them to diffuse through the phospholipid bilayer
• Absorption of lipids

  Products of lipid digestion diffuse across the cell surface membrane in micelles

  In the cell, products are reformed into triglycerides by the ER and Golgi apparatus

  Triglycerides are packaged into vesicles (called chylomicrons) and leave the cell (exocytosis) and move into lymph vessels
• Absorbtion of amino acids

  Facilitated diffusion of amino acids into the epithelial cell with the concentration gradient.

  Sodium actively transported out of the cell and into blood=lower sodium concentration in the cell than the ileum lumen

  sodium diffuses into the cell from the ileum lumen across a sodium-dependent amino acid carrier protein, carrying an amino acid with it.