Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download protein digest.99
Document related concepts
Monoclonal antibody wikipedia , lookup
Lipid signaling wikipedia , lookup
Polyclonal B cell response wikipedia , lookup
Biochemical cascade wikipedia , lookup
Paracrine signalling wikipedia , lookup
Signal transduction wikipedia , lookup
Ribosomally synthesized and post-translationally modified peptides wikipedia , lookup
Fatty acid metabolism wikipedia , lookup
Protein–protein interaction wikipedia , lookup
Magnesium transporter wikipedia , lookup
Metalloprotein wikipedia , lookup
Western blot wikipedia , lookup
Peptide synthesis wikipedia , lookup
Point mutation wikipedia , lookup
Two-hybrid screening wikipedia , lookup
Protein structure prediction wikipedia , lookup
Genetic code wikipedia , lookup
Biosynthesis wikipedia , lookup
Amino acid synthesis wikipedia , lookup
Transcript
Bio-molecules in diet Polymers monomers Proteins amino acids peptide Carbohydrates glucose glycosidic fatty acids ester Lipids Protein structure linkage glycerol digestive tract liver stomach pancreas +H H H-N - C H H H HH O H H O -C-N-C-C-N-C-C-N O CH3 H peptide bond digestive tract - mucus lines digestion tract and prevents damage to mucosal cells from acid and degradative enzymes duodenum Mucus • mucus is an acid glycoprotein • mucus protects the cells lining the digestive tract from: – HCl in stomach – proteases in stomach and small intestine Structure of mucus protein backbone oligosacc. chains saccharide side chains of mucus - O-C=O O-C=O O-C=O N-Ac Glucosamine -asn-leu-lys-ser-ala-met-phe- protein backbone Mucus protects lining from pepsin • mucus lines stomach wall and prevents pepsin from contacting mucosal cells • bacteria sometimes penetrate mucus layer causing ulcers in stomach lining Mucus provides sink for protons • pH of stomach fluid is below 2.0 • negative charges on COO groups of mucus sidechains sop up millions of protons • increases the pH along stomach lining to near 5 Enzymes which digest proteins in gut • pepsin in the stomach • • trypsin, chymotrypsin and carboxypeptidase in duodenum Zymogens Zymogens • zymogens are large precursor proteins which must be trimmed to become active enzymes • trypsinogen, chymotrypsinogen procarboxypeptidase are secreted from pancreas into duodenum • • these proteins are zymogens, inactive until trypsin cleaves peptides from each • many digestive enzymes are secreted as larger proteins, then trimmed by proteases Products of digestion Amino Acid structure • trypsin, chymotrypsin are peptidases which cleave peptide bonds between specific amino acids + H H OH -N - C - C = O H | R • • products are free amino acids, dipeptides, etc. Amino Acid transport Amino Acid transport proteins • free amino acids bind to specific transport proteins in cell membranes of intestinal cells • • amino acids are then transported into intestinal cells and sent to blood stream • at least 6 different a.a. transport proteins exist in human cell membranes Amino Acid tpt. proteins Duodenum lining tpt. protein acidic basic neutral proline specificity asp, glu arg, lys, his uncharged amino acids pro, OH-pro • each is specific for different set of amino acids lumen mucosal cell villus basement membrane sub-mucosa - smooth muscle intestinal mucosa cell Transport of amino acids Na+ pump a.a. transport proteins - amino acids are transported into human cells only DOWN a Na+ gradient - Na+ is transported out of the cell by the Na+/K+ pump (a protein found in all cell membranes) nucleus microvilli Transport of amino acids Na+ • amino acids enter mucosal cells in duodenum and move into capillary beds to portal vein Na+ K+ phenylalanine binding site amino acid transport protein Amino Acids move from intestinal cells to blood inside cell Na+ Na+ gradient is essential • amino acids enter cells by binding to specific a.a. transport proteins and riding down Na+ gradient • Na+ pump requires ATP and is essential for a.a. transport • amino acids are removed from blood by all cells in the body Insulin stimulates a.a. transport • amino acid transport into muscle cells is stimulated by insulin binding to receptor protein in muscle cell membrane Insulin stimulates a.a. transport Fate of exogenous amino acids in cells • insulin is secreted by pancreas into blood stream when [glucose] is high in blood • [amino acids] seem to have little effect on insulin secretion • first priority seems to be for protein synthesis in cells Nutritive classification Estimated requirements* Essential lys trp phe met thr leu, ile, val Semi essential arg tyr cys gly ser his Non essential glu, gln asp, asn ala pro OH-pro Amino Acid content for High quality protein lys trp phe & tyr met & cys his 51 11 73 26 17 *mg/gm. protein ile thr leu val 42 35 70 48 • excess amino acids are degraded and NH3 groups stored to make new a.a. amino acid 3-6 mo. 10 yrs. adult lys trp phe&tyr met&cys his leu 96 19 132 45 33 128 44 4 22 22 ? 42 12 3 16 10 ? 16 *mg/Kg./d Best quality proteins Protein human milk cow’s milk egg albumin beef steak plants Chemical score 100 95 100 98 60-70 Biological score 95 81 87 93 ~ 50 Synthesis of non-essential amino acids • all the non-essential a.a. may be formed from intermediates in the carbon skeleton of metabolism glu g-6-P f-6-P r-5-P f-1,6-diP pro ala OAA PEP malate malate pyr pyr pyr OAA Non-essential a.a. Serum Glu:Pyr Transaminase - present in liver cells; low levels in cardiac muscle cells - normal ratio: SGOT / SGPT = 1 - after heart attack, ratio is greater than 1, sometimes > 40 Amino Acid Synthesis Pathways glycogen glu SGPT acetyl Co A citrate OAA asp G glu Amino Acid synthesis pathways • Regulation: – 1. endprod. inhibits activity of 1st enzyme in pathway – 2. endprod. inhibits synthesis of 1st enzyme in pathway • Main function: a. a.a. for protein synthesis b. a.a. used to make hormones c. a.a. used for C and energy • Substrates: pyr, OAA, aKG, glu • Endproducts: ala, asp, glu, pro asn, gln Transaminases • ala, asp, glu are formed directly from Carbon Skeleton intermediate by transaminase enzymes • transaminases catalyze exchange of an amino group (donor a.a.) for a keto group Transamination phe + OAA phenyl + asp pyruvate O=C-O O=C-O HC-NH3 C=O H-C-H H-C-H O=C-O amino acid Transamination keto acid O=C-O C=O H-C-H O=C-O HC-NH3 H-C-H O=C-O keto acid amino acid SGOT Serum Glu:OAA Transaminase - present in cardiac muscle tissue but little in liver SGOTase glu + OAA a-KG + asp O=C-O O=C-O HC-NH3 C=O H-C-H H-C-H H-C-H O=C-O O=C-O amino acid keto acid O=C-O C=O H-C-H H-C-H O=C-O keto acid O=C-O HC-NH3 H-C-H O=C-O amino acid SGPT Serum Glu:Pyr Transaminase - present in liver cells; low levels in cardiac muscle cells - normal ratio: SGOT / SGPT = 1 - a rise in SGOT levels in blood stream indicates lyzing of heart muscle cells glutamine synthesis glutamine (gln) stores and transports excess amino groups through blood stream glu COO COO gln HC-NH3 HC-NH3 NH4+ CH CH CH CH O=C - NH2 O=C-O - after heart attack, ratio is greater than 1, sometimes > 40 Protein degradation All proteins are degraded (turned over) in all cells regularly. Ubiquitin is a small peptide that marks proteins for degradation . Protein degradation Ubiquitin - is peptide found in all cells - attaches to N-terminal of protein to be degraded by cellular proteases Protein degradation Some proteins are degraded very slowly; live in cells for many months to years long-lived proteins: aldolase cytochrome b lactate DHase Protein degradation Some proteins have short life and are degraded after a few days. e.g. - HMG CoA reductase - some muscle proteins - proteins with defects (mutant proteins)
