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4.) Carbohydrates Structure

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  1. Front
    Most dietary carbohydrate before absorption
    Back
    Not absorbed as polysaccharide or disaccharide and must first be digested to monosaccharides
  2. Front
    Final absorbable sugars from carbohydrate digestion
    Back
    Glucose, galactose, and fructose
  3. Front
    Where carbohydrate digestion begins
    Back
    Mouth
  4. Front
    What happens to carbohydrate digestion in the stomach
    Back
    It pauses because gastric acidity inactivates salivary amylase
  5. Front
    Main site where carbohydrate digestion continues
    Back
    Small intestine, especially the duodenum and upper jejunum
  6. Front
    Role of amylases in carbohydrate digestion
    Back
    Digest large glucose polymers
  7. Front
    Role of brush border disaccharidases
    Back
    Finish carbohydrate digestion to monosaccharides
  8. Front
    Only form of carbohydrate that is absorbed
    Back
    Monosaccharides
  9. Front
    Glucose classification
    Back
    Glucose is an aldohexose
  10. Front
    Meaning of aldo- in aldohexose
    Back
    Contains an aldehyde in the open-chain form
  11. Front
    Meaning of hexose
    Back
    Contains 6 carbons
  12. Front
    Main form of glucose in solution
    Back
    Ring form
  13. Front
    High-yield relationship between glucose and galactose
    Back
    Both are aldohexoses
  14. Front
    Physiologic importance of glucose
    Back
    Main blood sugar and major energy source for the majority of cells
  15. Front
    Ring form of glucose commonly shown in metabolism slides
    Back
    Six-membered ring
  16. Front
    Fructose classification
    Back
    Fructose is a ketohexose
  17. Front
    Meaning of keto- in ketohexose
    Back
    Contains a ketone in the open-chain form
  18. Front
    High-yield distinction between glucose and fructose
    Back
    Glucose is an aldohexose, whereas fructose is a ketohexose
  19. Front
    Common ring form of fructose in metabolism diagrams
    Back
    Five-membered ring form
  20. Front
    Galactose classification
    Back
    Galactose is an aldohexose
  21. Front
    Relationship of galactose to glucose
    Back
    Galactose is very similar to glucose but differs in orientation of one hydroxyl group
  22. Front
    Relationship between glucose and galactose
    Back
    They are epimers
  23. Front
    Importance of galactose
    Back
    It is a component of lactose and can be converted into glycolysis intermediates through galactose metabolism
  24. Front
    Composition of lactose
    Back
    Galactose + glucose
  25. Front
    Glycosidic bond in lactose
    Back
    β(1→4)
  26. Front
    Specific linkage in lactose
    Back
    Carbon 1 of β-galactose linked to carbon 4 of glucose
  27. Front
    Physiologic source of lactose
    Back
    Milk sugar
  28. Front
    Enzyme that digests lactose
    Back
    Lactase
  29. Front
    Clinical condition caused by lactase deficiency
    Back
    Lactose intolerance
  30. Front
    Composition of sucrose
    Back
    Glucose + fructose
  31. Front
    Glycosidic bond in sucrose
    Back
    α(1→2)
  32. Front
    Enzyme that digests sucrose
    Back
    Sucrase
  33. Front
    Products of sucrose digestion
    Back
    Glucose and fructose
  34. Front
    Common name for sucrose
    Back
    Table sugar
  35. Front
    Major plant storage polysaccharide
    Back
    Starch
  36. Front
    Components of starch
    Back
    Amylose and amylopectin
  37. Front
    Amylose structure
    Back
    Unbranched polymer of glucose with α(1→4) glycosidic bonds
  38. Front
    Amylopectin structure
    Back
    Branched polymer of glucose with α(1→4) bonds in chains and α(1→6) bonds at branch points
  39. Front
    High-yield starch vs glycogen distinction
    Back
    Starch is plant storage polysaccharide, whereas glycogen is animal storage polysaccharide
  40. Front
    Shared bond pattern of starch and glycogen
    Back
    Both have α(1→4) main chains, and branched forms have α(1→6) branch points
  41. Front
    Main storage carbohydrate in animals
    Back
    Glycogen
  42. Front
    Composition of glycogen
    Back
    Polymer of glucose
  43. Front
    Bond pattern in glycogen
    Back
    α(1→4) bonds in linear chains and α(1→6) bonds at branch points
  44. Front
    Branching difference between glycogen and amylopectin
    Back
    Glycogen is more highly branched than amylopectin
  45. Front
    Major glycogen stores in humans
    Back
    Liver and muscle
  46. Front
    Monosaccharide structure summary
    Back
    Glucose = aldohexose, galactose = aldohexose, fructose = ketohexose
  47. Front
    Disaccharide structure summary
    Back
    Lactose = galactose + glucose with β(1→4), and sucrose = glucose + fructose with α(1→2)
  48. Front
    Polysaccharide structure summary
    Back
    Starch contains amylose with α(1→4) and amylopectin with α(1→4) plus α(1→6), whereas glycogen contains α(1→4) plus α(1→6) and is highly branched
  49. Front
    Big picture of carbohydrate digestion
    Back
    Begins in the mouth, stops in the stomach, continues in the small intestine, and final breakdown occurs at the brush border of intestinal epithelial cells
  50. Front
    Salivary α-amylase action
    Back
    Initiates digestion of starch and glycogen in the mouth
  51. Front
    Substrates of salivary α-amylase
    Back
    Starch and glycogen
  52. Front
    Bond hydrolyzed by salivary α-amylase
    Back
    Random α(1→4) bonds
  53. Front
    Bonds not broken by salivary α-amylase
    Back
    α(1→6) branch bonds and β(1→4) bonds
  54. Front
    Products of salivary α-amylase digestion
    Back
    Smaller oligosaccharides, dextrins, and some disaccharides
  55. Front
    Why humans cannot digest cellulose
    Back
    Cellulose contains β(1→4) linkages and humans do not produce the needed enzyme
  56. Front
    Reason carbohydrate digestion halts in the stomach
    Back
    High acidity inactivates salivary α-amylase
  57. Front
    Very testable stomach concept for carbohydrate digestion
    Back
    Digestion starts in the mouth but does not continue well in the stomach due to low pH
  58. Front
    What neutralizes acidic chyme in the small intestine
    Back
    Bicarbonate from the pancreas
  59. Front
    Pancreatic α-amylase action
    Back
    Continues digestion of starch and glycogen in the small intestine
  60. Front
    Bond hydrolyzed by pancreatic α-amylase
    Back
    α(1→4) bonds in starch and glycogen
  61. Front
    Bonds not cut by pancreatic α-amylase
    Back
    α(1→6) branch bonds, terminal disaccharide linkages, and β linkages
  62. Front
    Why brush border enzymes are still needed after amylase digestion
    Back
    Amylases do not complete digestion to monosaccharides
  63. Front
    Location of brush border disaccharidases
    Back
    Luminal or apical brush border of enterocytes
  64. Front
    Function of isomaltase
    Back
    Cleaves α(1→6) bonds in isomaltose and branched products
  65. Front
    Function of maltase
    Back
    Cleaves α(1→4) bonds in maltose and maltotriose to produce glucose
  66. Front
    Function of sucrase
    Back
    Cleaves α(1→2) bonds in sucrose to yield glucose and fructose
  67. Front
    Other name for lactase
    Back
    β-Galactosidase
  68. Front
    Function of lactase
    Back
    Cleaves β(1→4) bonds in lactose to yield galactose and glucose
  69. Front
    Function of trehalase
    Back
    Cleaves trehalose
  70. Front
    Very high-yield enzyme-bond matching
    Back
    Amylase cleaves α(1→4) in starch and glycogen, isomaltase cleaves α(1→6), maltase cleaves α(1→4) in maltose and maltotriose, sucrase cleaves α(1→2) in sucrose, and lactase cleaves β(1→4) in lactose
  71. Front
    Final products of carbohydrate digestion that are absorbed
    Back
    Glucose, galactose, and fructose
  72. Front
    Carbohydrates not absorbed directly
    Back
    Starch, glycogen, lactose, sucrose, maltose, and dextrins
  73. Front
    Why starch, glycogen, lactose, sucrose, maltose, and dextrins are not absorbed
    Back
    They must be broken down to monosaccharides first
  74. Front
    Apical transporter for glucose in enterocytes
    Back
    SGLT-1
  75. Front
    Apical transporter for galactose in enterocytes
    Back
    SGLT-1
  76. Front
    Type of intestinal uptake for glucose and galactose
    Back
    Secondary active transport with Na+
  77. Front
    Why SGLT-1 transport is secondary active transport
    Back
    It depends on the Na+ gradient rather than directly using ATP at the transporter itself
  78. Front
    Transporter that maintains the Na+ gradient for SGLT-1
    Back
    Na+/K+ ATPase on the basolateral membrane
  79. Front
    Apical transporter for fructose in enterocytes
    Back
    GLUT-5
  80. Front
    Energy dependence of fructose uptake
    Back
    Na+-independent and does not directly require energy
  81. Front
    Basolateral exit transporter for glucose, galactose, and fructose
    Back
    GLUT-2
  82. Front
    Destination of absorbed monosaccharides after leaving enterocytes
    Back
    Portal blood
  83. Front
    Clean transport summary for carbohydrate absorption
    Back
    Apical membrane: glucose and galactose use SGLT-1, fructose uses GLUT-5; basolateral membrane: all three leave via GLUT-2; Na+/K+ ATPase maintains the sodium gradient that drives SGLT-1
  84. Front
    Definition of lactose intolerance
    Back
    Inability to properly digest lactose because of low lactase activity
  85. Front
    Primary defect in lactose intolerance
    Back
    Lactose is not broken into glucose and galactose
  86. Front
    Why undigested lactose remains in the intestinal lumen
    Back
    Only monosaccharides are absorbed, so lactose cannot be absorbed intact
  87. Front
    What happens to undigested lactose
    Back
    It stays in the intestinal lumen and passes into the large intestine
  88. Front
    Osmotic effect of undigested lactose
    Back
    Undigested lactose is osmotically active and pulls water into the intestine, causing osmotic diarrhea
  89. Front
    Bacterial effect on undigested lactose
    Back
    Colonic bacteria ferment it
  90. Front
    Products of bacterial fermentation of undigested lactose
    Back
    Organic acids or small osmotically active compounds, CO2, and H2 gas
  91. Front
    Symptoms caused by bacterial fermentation of lactose
    Back
    Bloating, flatulence, abdominal cramps, and diarrhea
  92. Front
    Causes of lactase deficiency
    Back
    May be genetic or acquired after injury to the small intestinal mucosa
  93. Front
    Primary lactase deficiency
    Back
    Genetic lactase deficiency
  94. Front
    Secondary lactase deficiency
    Back
    Acquired lactase deficiency, such as after small intestinal mucosal injury
  95. Front
    Effect of severe diarrhea on brush border enzymes
    Back
    Brush border enzymes are rapidly lost, so temporary trouble with dairy can occur during recovery
  96. Front
    High-yield takeaway on lactase deficiency
    Back
    Lactase deficiency may be primary or secondary
  97. Front
    Important distinction in lactose intolerance
    Back
    It is a digestion problem, not a monosaccharide transporter problem
  98. Front
    Why lactose intolerance is not a transporter defect
    Back
    Glucose and galactose transporters may be normal, but lactose must first be split by lactase before absorption
  99. Front
    High-yield starch vs glycogen comparison
    Back
    Both are glucose polymers with α(1→4) chains and α(1→6) branches, glycogen is more highly branched, starch is plant, and glycogen is animal
  100. Front
    High-yield lactose vs sucrose comparison
    Back
    Lactose = galactose + glucose with β(1→4), whereas sucrose = glucose + fructose with α(1→2)
  101. Front
    High-yield glucose and galactose vs fructose absorption comparison
    Back
    Glucose and galactose use SGLT-1, fructose uses GLUT-5, and all exit via GLUT-2
  102. Front
    High-yield amylase vs disaccharidase comparison
    Back
    Amylase works on large glucose polymers and cuts α(1→4), whereas brush border enzymes complete digestion to monosaccharides
  103. Front
    Super high-yield cellulose fact
    Back
    Humans cannot digest cellulose because it contains β(1→4) bonds
  104. Front
    Super high-yield stomach fact for carbohydrate digestion
    Back
    Carbohydrate digestion stops in the stomach because acid inactivates salivary amylase
  105. Front
    Super high-yield site of final carbohydrate digestion
    Back
    The final digestive steps occur at the brush border in the duodenum and upper jejunum
  106. Front
    Super high-yield absorption fact
    Back
    Only monosaccharides are absorbed
  107. Front
    Super high-yield consequence of lactase deficiency
    Back
    Lactase deficiency causes osmotic diarrhea and gas because lactose remains in the lumen and is fermented by bacteria

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