Post on 01-May-2018
Digestion of Biomolecules
Stryer Short courseChapter 14
Hydrolysis Reactions
• Proteins amino acids– Proteases, peptidases
• Complex carbohydrates monosaccharides– amylase
• Triacylglycerides fatty acids– lipase
Zymogens
• Proenzymes—inactive precursors• Cannot release digestive enzymes everywhere!
• Pepsinogen pepsin: autocatalysis at low pH
Pancreatic Zymogens
Mechanism
• Protease activates trypsin
• Trypsin activates other zymogens
Stomach
• Highly acidic, denaturing environment
• Pepsin begins work• Acidic, partially digested food enters intestine– Activates secretin to neutralize adic
– Activates hormone causing release of pancreatic zymogens and bile salts
Stomach acid
• Prilosec: irreversible inhibitor of proton, potassium pump
Error in carbonic anhydrase
Proteins in the Intestine
• Protein digestion continues with proteases in lumen• Transporter proteins essential—basis of some genetic diseases
• Amino acids then sent to liver• Gluten sensitivity
Carbohydrates in the Intestine
• ‐amylase• Limiting dextrins• Maltase, sucrose, lactase, glucosidase, dextrinase all work to digest to monosaccharides
Carbohydrate Transporters
Lipid Digestion
• Complicated by insolubility
• Emulsion form in stomach
• Extra steps of degradation/re‐assembly
• Bile salts– Cholesterol lowering medications
Pancreatic Lipases
• Zymogens• Fatty acids and MAG• Miscelle formation
Transport to Liver
• Fatty acid binding proteins
• Fatty acid transport proteins
• Smooth enoplasmicreticulum
• chylomycrons