* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Digestion & absorption of carbs & proteins
Paracrine signalling wikipedia , lookup
Evolution of metal ions in biological systems wikipedia , lookup
Magnesium transporter wikipedia , lookup
Protein–protein interaction wikipedia , lookup
Point mutation wikipedia , lookup
Signal transduction wikipedia , lookup
Polyclonal B cell response wikipedia , lookup
Two-hybrid screening wikipedia , lookup
Catalytic triad wikipedia , lookup
Human digestive system wikipedia , lookup
Western blot wikipedia , lookup
Fatty acid metabolism wikipedia , lookup
Protein structure prediction wikipedia , lookup
Genetic code wikipedia , lookup
Peptide synthesis wikipedia , lookup
Amino acid synthesis wikipedia , lookup
Ribosomally synthesized and post-translationally modified peptides wikipedia , lookup
Biosynthesis wikipedia , lookup
Section 10 Nutrients & Their Functions 1. Acquiring nutrients Digestion & absorption of carbohydrates & proteins 1/3/06 Section 10 Acquiring Nutrients Overview nutrients digestion, absorption glucose, amino acids, fats distribution precursors, available fuels metabolism macromolecules, energy, end products 1 Digestion: general features general function: convert nutrients into absorbable form larger molecules (macro) smaller molecules O O chemical reaction: hydrolysis H2O + RX –YR' RXOH + HYR' where X = C, P Y = O, N reaction catalyzed by hydrolases major nutrients hydrolase type poly, oligosaccharides glycosidase proteins, peptides protease, peptidase fats (triglycerides) esterase minor nutrients O H 2O O O OH HO bond cleaved glycosidic peptide ester phospholipids, nucleic acids phospholipase, nuclease phosphoester esters (e.g., cholesterol, retinol) esterases ester 2 Activation of hydrolases noncovalent activator binds reversibly to enzyme examples: enzyme activator a-amylase Cl – lipase colipase covalent activator catalyzes hydrolysis of one or more peptide bonds of precursor activator precursor active enzyme (proenzyme or zymogen) examples: 3 HCl pepsinogen pepsin trypsin proelastase elastase Carbohydrates: digestion (poly oligo) only monosaccharides are absorbable Stage I: polysaccharides oligosaccharides enzyme: a-amylase (specificity: internal a1,4 glucosidic bonds) sources: salivary glands (minor) & pancreas (major) substrates: amylose (only a1,4 links) amylopectin: products: maltose, maltotriose * a1,6 linkage * indicates typical a-amylase hydrolysis site * * * * products: 4 maltotriose (glc3) an a-limit dextrin maltose Carbohydrates: digestion (oligo mono) Stage II: oligosaccharides monosaccharides source of enzymes: mucosal cell surface (brush border) a-limit dextrins maltose glc3 sucrose lactose 5 isomaltase (a-dextrinase) α1,6 glucosidic bonds 2 glc maltase 3 glc " glc + fructose sucrase glc + gal lactase (inducible) glc3 + glc + maltose a-limit dextrins: (glc)4-9 with one a1,6 linkage glc: glucose gal: galactose Carbohydrates: absorption from lumen frc & mannose facilitated diffusion (carrier-mediated) glc & gal transported against concentration gradient + cotransport (Na gradient-driven symport) aka secondary active transport pentoses, 6 others absorbed via simple diffusion Na+ glc symport protein glc-Na+ symport animation for “snapshots” of this animation, see the next slide stop animation by clicking browser’s Stop button resume animation by going to another slide, then returning to this one 7 glc-Na+ symport protein + glc-Na symport mechanism 1. outer gate open, sites unoccupied 2. sites occupied, outer gate closing 3. inner gate opening 4. Na+, glc dissociating 5. inner gate closed, outer gate opening glc-Na+ symport protein lumen of small intestine Glucose movement: lumen blood transport into mucosal cell (enterocyte) mucosal cell across luminal (apical) membrane against concn. gradient + Na glc symport transport glucose (lower conc.) Na+ glucose (higher conc.) out of mucosal cell across contraluminal (basolateral) membrane down concn. gradient glc transporter (GLUT2) + glc Na Na+ transporter (symport) Na+ K+ 8 GLUT2 glucose carrier (facil. diffusion) Na+,K+ ATPase glucose (lower conc.) K+ Na+ interstitial fluid blood Proteins: digestion to peptides & amino acids only amino acids & some small peptides absorbable stomach: food polypeptides stimulate G-cells in pyloric region to secrete the hormone gastrin gastrin stimulates parietal cells to secrete HCl effects of HCl 9 denatures (unfolds) proteins solubilizes iron, other metals (ions) inactivates pathogenic organisms (antiseptic) stimulates secretion of secretin & cholecystokinin (CCK) activates pepsinogen in bulimia, erodes enamel Proteins: gastric digestion peptidases (proteases, proteolytic enzymes) exopeptidases: peptide bonds next to N- or C-terminus endopeptidases: bonds not next to N- or C-terminus pepsin O O O O H3NCC–NCC–NCC–NCC–NCCOO– exo endo endo exo + endopeptidase secreted as pepsinogen by chief cells (stimulus: gastrin) activation: catalyzed by HCl, pepsin (self-activation) specificity: bonds next to aromatic side chains (phe, tyr, trp) an aspartate protease (2 asp at active site; slide 14) main result of passage through stomach: polypeptides unfolded & converted to large peptides 10 Gastric secretions & digestion HCl secretion by parietal cells pepsinogen secretion by chief cells pepsinogen activation by HCl pepsin autocatalysis: product activation of precursor pepsinogen 360 42 pepsin 11 HCl, pepsin Sherwood, Fig. 16-11 Proteins: intestinal secretions & digestion HCl, peptides in chyme stimulate duodenum to secrete CCK: stimulates pancreas to secrete enzyme -rich juice – secretin: stimulates pancreas to secrete HCO3 -rich juice gastric inhibitory peptide: inhibits antral contractions HCO3 – raises pH of chyme to 7- 8 pancreatic proteases: trypsin (an endopeptidase) secreted as trypsinogen trypsinogen activated by enteropeptidase* (mucosal cells) & by trypsin (self-activation) important as activator of many other digestive enzymes specificity: bonds next to cationic side chains (lys, arg) a serine protease (contains a catalytic triad; slide 14) 12 * aka enterokinase Intestinal digestion by peptidases pancreas also secretes trypsin inhibitor other pancreatic peptidases peptidase type activator side chain specificity chymotrypsin endo trypsin nonpolar, aromatic elastase " " small, aliphatic carboxypeptidase A exo " nonpolar, aromatic " B " " cationic mucosal cell luminal surface peptidases 13 aminopeptidase (peptide bond next to N-terminus) dipeptidase (dipeptides) Protease classes or families all proteases belong to 1 of 4 classes classification based on main catalytic site feature protease class examples serine (section 4) trypsin, chymotrypsin, elastase, thrombin, plasmin zinc " carboxypeptidases, thermolysin thiol (cysteine) papain, cathepsins (lysosomes) aspartate pepsin, renin, HIV-1 protease 14 within a class, substrate specificity due to structure of part of the active site: the specificity site Serine proteases: specificity pocket binding pocket structured to favor side chains on substrate that are: nonpolar/aromatic chymotrypsin cationic trypsin small elastase gly 226 gly 226 ser 189 15 N gly 216 chymotrypsin N + – N gly 216 thr 216 val 226 asp 189 trypsin elastase Absorption of peptides & amino acids from GI lumen amino acids + Na gradient-driven symports (cotransport) mechanism same as glucose–Na+ symport at least 6 kinds of symport proteins specificities by amino acid types examples: small, polar side chains (ala, ser, thr) cationic side chains (lys, arg) anionic side chains (asp, glu) 16 Absorption of peptides & amino acids some small peptides are absorbed mostly di- & tripeptides + H gradient-driven symport absorbed peptides hydrolyzed to amino acids by cytosolic peptidases amino acids reach portal blood via facilitated diffusion across contraluminal membrane of mucosal cells mechanism same as monosaccharide systems specific transmembrane carrier proteins 17 Amino acids, peptides movement: lumen blood analogous to glc movement (slide 8) absorption via symports lumen of small intestine Na+ amino acids small H+ peptides H+ peptide symport Na+ aa symport mucosal cell Na+ aa: Na+ gradient-driven + peptides: H gradient-driven H+ in amino acids peptidases small cytosol: peptides amino acids aa’s cross contraluminal membrane via facilitated diffusion carriers amino acid peptides Na+ K+ carriers (facil. diffusion) amino acids 18 interstitial fluid Na+,K+ ATPase K+ Na+ blood Study questions Describe step-by-step the processes of digestion, absorption, and distribution of proteins. Include the roles of enzymes, activators, hormones, and membrane transport. Do the same for carbohydrates. Next time: Digestion & absorption of lipids