Digestion and absorption of proteins

• What are the complex dietary molecules involved in digestion?

  Protein, Fat, Carbohydrates
• What is the role of digestive enzymes in digestion?

  They facilitate hydrolytic cleavage of molecules
• What is the energy yield from the oxidation of carbohydrates?

  It yields energy for bodily functions
• Why are proteins essential for children and critically ill patients?

  • Optimal growth and development
  • Recovery for convalescing patients
  • Support for critically ill patients
• Where does protein digestion primarily occur?

  In the stomach and small intestine

  
• What type of enzymes are involved in protein digestion in the stomach?

  Proteases are the enzymes involved

  
• What is the pH level of the stomach environment?

  pH = 2.0
• What enzyme is released by chief cells in the stomach?

  The enzyme is called pepsinogen
• What is pepsinogen classified as?

  It belongs to the family of zymogens
• How is pepsinogen activated?

  By the action of HCl in the stomach
• What type of enzyme is pepsin?

  Endopeptidase
• What does pepsin cleave at?

  Amino side of hydrophobic amino acids
• What enzymes are released by the pancreas for protein digestion?

  Trypsinogen, Chymotrypsinogen, Proelastase, Procarboxypeptidase
• What is enteropeptidase's role in protein digestion?

  It activates trypsinogen to trypsin
• What type of enzyme is trypsin?

  Endopeptidase
• What is the catalytic mechanism of trypsin?

  Serine protease
• What is the cleavage specificity of trypsin?

  Adjacent to basic amino acids
• What is the cleavage specificity of chymotrypsin?

  Adjacent to hydrophobic amino acids
• What is the cleavage specificity of elastase?

  Adjacent to small amino acids
• What is the cleavage specificity of carboxypeptidase A?

  Hydrophobic amino acids at C-terminus
• What is the cleavage specificity of carboxypeptidase B?

  Basic amino acids at C-terminus
• What enzymes are anchored to the microvilli of the brush border?

  • Aminopeptidase
  • Endopeptidase
  • Carboxypeptidase
  • Dipeptidase
• What is the surface area of the brush border?

  200 m², about half a basketball court
• What are the products of protein digestion?

  • Tetra-peptides
  • Tri-peptides
  • Di-peptides
  • Amino acids
• What are the sites and enzymes involved in protein digestion?

  Sites:

  • Stomach
  • Small intestine

  
  

  Enzymes:

  • Pepsin
  • Trypsin
  • Chymotrypsin
  • Elastase
  • Carboxypeptidase A and B
  • Brush border enzymes

  
• What is the primary function of the villus in absorption?

  Transportation of digestion products across membranes
• What is the length range of a villus?

  0.5 to 1.5 mm
• What type of epithelium covers the villus?

  Simple columnar epithelium

  
• What are the mechanisms of absorption in enterocytes?

  Passive diffusion, facilitated diffusion, active transport

  
• What form of protein is primarily absorbed in the enterocyte?

  Peptides are primarily absorbed
• How is peptide absorption coupled in enterocytes?

  Coupled to H+ gradient

  
• What happens to peptides in the enterocyte after absorption?

  They are metabolized into free amino acids

  
• How are free amino acids transported across the basolateral membrane?

  By facilitated diffusion and co-transport
• Where are amino acids transported after absorption?

  To the liver via the hepatic portal vein
• What happens to glutamate and aspartate after absorption?

  They are utilized as energy, not transported