digestion and absorption ppt

• Digestion reactions1


  Larger molecules are hydrolysed into smaller molecules

  Smaller molecules are absorbed into blood in the small intestine

  These are hydrolysis reactions

  A molecule of water is added to break the bond
• Hydrolysis


  Add molecule of water to break the bond
• Enzymes


  • Use specific enzymes to catalyse reactions
  • These are specific due to the shape of their active site
  • Only this molecule can bind with the active site to form an enzyme-substrate complex
• The 4 polymers broken down into monomers

  • starch
  • cellulose
  • glycogen
  • polypeptides/proteins
• Digestion is the hydrolysis of large, insoluble substances to small(er), soluble substances
• Digestive enzymes


  • Amylase
  • Lactase
  • Sucrase
  • Maltase
  • Lipase
• Amylase


  • Substrate: starch
  • Products: maltose
  • Type of bond hydrolysed: glycosidic
• Lactase

  • Substrate: lactose
  • Products: glucose + galactose
  • Type of bond hydrolysed: glycosidic
• Sucrase

  • Substrate: sucrose
  • Products: glucose + fructose
  • Type of bond hydrolysed: glycosidic
• Maltase

  • Substrate: maltose
  • Products: glucose + glucose
  • Type of bond hydrolysed: glycosidic
• Lipase

  • Substrate: triglycerides
  • Products: monoglycerides + fatty acids
  • Type of bond hydrolysed: ester
• Small molecules like monosaccharides, amino acids, vitamins, minerals, fatty acids, glycerol do not need digesting
• Organs involved in digestion (& absorption)

  • Liver
  • Stomach
  • Gall bladder
  • Pancreas
  • Large intestine
  • Small intestine
  • Rectum
• Stomach


  Proteases secreted (e.g. pepsin)
• Gall bladder


  Stores & releases bile
• Liver


  Makes bile
• Large intestine


  Absorbs water
• Pancreas


  Secretes amylase, lipase, protease
• Small intestine


  • Absorption of small molecules
  • Disaccharidases & dipeptidases are found on the cell surface membrane of epithelial cells
• Digestionoverview


  Larger molecules hydrolysed into smaller ones by enzymes in lumen of ileum or on cell surface membrane of epithelial cells
• Absorption overview

  Smaller molecules absorbed across cells into blood
• Assimilationoverview


  Products of digestion transported to cells & used by cells
• Absorption of products of digestion (in the ileum)

  
  

  -Blood flow away from the ileum maintains concentration gradients so products of digestion continue to diffuse across

  -e.g glucose has a higher conc. outside of the epithelial cells. This happens as the glucose going through the epithelial cells by FD then into the villi which has a lower conc. & therefore it keeps moving out of the villi & repeating the process
• Digestion of triglycerides


  1. Fatty acids & monoglycerides are surrounded by bile salts to form micelles

  2. Fatty acids & monoglycerides are released and cross the cell surface membrane by simple diffusion

  3. Triglycerides are reformed and surrounded by protein to form chylomicrons

  4. Chylomicrons are secreted into the lymph vessel and then transported into the blood
• Digestion reactions 2

  It uses specific enzymes to catalyse the hydrolysis of specific bonds in specific molecules

  Enzymes are specific due to the shape of their active site which is only complimentary to the shape of the substrate and only this molecule can bind with the active site to form an E-S complex

  It breaks polymers down into their constituent monomers (what they're made up of) The 4 polymers are proteins, starch, glycogen and cellulose
• Digestion of carbohydrates

  • The hydrolysis of glycosidic bonds
  • Amylase- from the salivary glands and pancreas
  • Hydrolysis of starch to maltose
  • Disaccharidases are embedded in the c.s.m of epithelial cells of the ileum and these hydrolyse maltose, sucrose, and lactose
• Digestion of lipids

  • Hydrolysis of ester bonds
  • Lipase- from the pancreas
  • It hydrolyses triglycerides to monoglycerides and fatty acids
  • Bile salts- emulsify large lipid droplets into smaller ones providing a larger surface area for lipase to act= faster hydrolysis/digestion
• Digestion of proteins/polypeptides

  • Hydrolysis of peptide bonds
  • There's 3 types of protease involved- endo+exopeptidases, dipeptidases
• Digestion of proteins/polypeptides ?

  -Endopeptidases=hydrolyse internal peptide bonds creating more smaller polypeptides, providing more 'ends' for exopeptidases to act on for faster hydrolysis

  -Exopeptidases=hydrolyse end peptide bonds creating single amino acids

  -Dipeptidases=The combined action of both endo/exopeptidases leaves some dipeptides, dipeptidases hydrolyse these (the dipeptidases are embedded in the c.s.m like disaccharidases)
• Absorption of fatty acids and monoglycerides

  1. Bile salts= polar so cannot enter, they transport monoglycerides and fatty acids to the epithelial cell
  2. Fatty acids & monoglycerides= surrounded by bile salts to form micelles
  3. Fatty acids & monoglycerides released & cross the cell surface membrane by SDiffusion
  4. The fatty acids and monoglycerides reformed into triglycerides-done by golgi- & are now in the cytoplasm(= 70% water)the triglycerides are surrounded by protein to form chylomicrons
  5. Chylomicrons are secreted into the lymph vessel and transported into the blood
• Co-transport of glucose and sodium ions

  1. Sodium ions actively transported into the blood
  2. This keeps a low conc. of sodium ions in the cell because they're leaving and going into the blood
  3. So, sodium ions always have a conc. gradient to diffuse down into the cell, taking glucose with it (despite conc. gradient)
  4. Facilitated diffusion into the blood
  5. Overall this gets as much glucose out of the diet as possible
• Co-transport of amino acids & sodium ions

  1. Sodium ions are actively transported into the blood
  2. This keeps a low conc. of sodium ions in the cell because they are leaving and going into the blood
  3. So, sodium ions always have a conc. gradient to diffuse down into the cell, taking amino acids with it (despite the conc. gradient)
  4. Facilitated diffusion into the blood
• Which 2 enzymes are embedded in the c.s.m of an ileum epithelial cell?

  -Dipeptidases

  -Disaccharidases
• Why are some enzymes denatured as they pass through the various regions of the gut?

  E.g due to the acidic regions of the stomach