Digestion and absorption

• What types of enzymes are needed to break down carbohydrates

  salivary amylase

  pancreatic amylase

  disaccharidases

  maltase
• draw the word equation to show the complete breakdown of starch and the enzymes used 


  -
• name the enzymes required to break down the following disaccharides and state where the enzymes are made

  Maltose- maltase

  Lactose- lactase

  Sucrose- sucrase
• what is the name of the reaction that breaks down the polysaccharides and disaccharides into their monosaccharides 


  • hydrolysis reaction
• Describe how monosaccharides are absorbed into the blood from the lumen of the small intestine

  • food enters the mouth and is broken up by teeth and mixed with saliva
  • salivary amylase catalyses the hydrolysis of glycosidic bonds in starch to produce maltose
  • salivary amylase is denatured when it enters the stomach
  • pancreatic amylase is secreted into the small intestine and continues to hydrolyse the starch into maltose
  • disaccharidase enzymes are attached to the cell membranes of epithelial cells in the ileum
  • maltose is hydrolysed to glucose by maltase enzymes in the membranes of epithelial cells
  • the glucose can then be absorbed into the blood
• name the enzyme needed to break down lipids and state where this is produced

  lipase enzymes

  produced in the pancreas and transported to the ileum of the small intestine
• why are bile salts useful- 2 reasons

  • bile salts are produced by the liver and emulsify lipids
  • they cause lipids to form smaller droplets to increase surface area
• explain how monoglycerides and fatty acids are absorbed across the ileum epithelium

  • triglycerides are hydrolysed into a monoglyceride and 2 fatty acids, the reaction is catalysed by lipase enzymes
  • this involves the hydrolysis of ester bonds in lipids
  • bile salts are produced and emulsify lipids
  • the formation of small droplets greatly increases the surface area of lipids thats available for lipase to work on so leads to faster rates of hydrolysis
  • once the lipids have been hydrolysed by lipase, the monoglyceride and the 2 fatty acids stick with the bile salts to form micelles
  • micelles help the products of lipid digestion to be absorbed
• describe the action of exopeptidases

  they hydrolyse peptide bonds at the ends of the polypeptide molecule to release a single amino acid
• Describe the action of endopeptidases

  they hydrolyse ethe peptide bonds in the middle of a polypeptide to produce shorter poly peptides, increasing the number of ends for exopeptidases to work
• where are exopeptidases and endopeptidases produced

  endopeptidases - stomach + pancreas

  exopeptidases - pancreas
• what is a dipeptidase

  • an enzyme that works specifically on dipeptides
  • the hydrolyse the peptide bond between the amino acids in the disaccharide
• where are dipeptidases typically found

  they are found in the cell surface membrane of epithelial cells in the small intestine
• describe how amino acids are absorbed into the blood from the lumen of the small intestine

  amino acids are absorbed into the blood by co-transport

  1. sodium ions are actively transported out of the epithelial cell, into blood using energy from the hydrolysis of ATP and a specific carrier protein
  2. this creates a sodium ion concentration gradient from the lumen of the small intestine, into the epithelial cell
  3. so glucose and sodium ions are co-transported across the membrane, down the sodium ion concentration gradient via facilitated diffusion. this involves a specific carrier protein that will only carry glucose and sodium molecules at the same time
  4. the glucose is now transported from the epithelial cell into the blood via facilitated diffusion down a concentration gradient, using a specific carrier protein