Intro to Proteins Made up of amino acids Functions o Growth and maintenance o Enzymes o Hormones o Fluid balance o Acid base balance o Transportation o Antibodies o Energy Amino Acids Structural Classification Side chain determines function know which molecule belongs to what group Aliphatic Side Chains 5 o Glycine Gly Side Chain with OH group 2 Side Chains with sulfur 2 o Alanine Ala o Valine Val o Leucine Leu o Isoleucine Ile o Serine Ser o Threonine Thr o Cysteine Cys o Methionine Met o Aspartic acid Asp o Glutamic acid Glu o Asparagine Asn o Glutamine Gln o Arginine Arg o Lysine Lys o Histidine His o Phenylalanine Phe Side Chains with basic groups 3 Side Chains with aromatic rings 3 Side Chains with carboxyl or amide group 4 o Tyrosine Tyr o Tryptophan Trp o Prolie Pro Imino acid Essentiality Non essential aa s Essential 9 o We can synthesize them o We cannot synthesize them o Must be consumed from diet o Synthesized by plants and bacteria o EX His Leu Lys Ile Phe Val Met Trp Thr o EX Cys Tyr o These can be made from essential aa s o Met Cys Phe Tyr Conditionally Essential Functions of Amino Acids Energy o Fate determined by energy needs of cell Gluconeogenesis If cell needs energy Krebs intermediates Malate formation Malate OAA PEP glucose Fatty Acid Synthesis Excess energy Malate Pyruvate Acetyl CoA Fatty Acid Synthesis o Glucogenic vs ketogenic Glucogenic can be converted to glucose Ketogenic can be converted to ketone bodies Glucogenic and ketogenic Buffer by accepting protons o Ex Amino acids that form hemoglobin accept H serves as a buffer in RBC s Synthesis of Neurotransmitters o Tyrosine dopamine norepinephrine epinephrine o Glutamate gamma amino butyric acid o Tryptophan serotonin o Amino acids are linked by peptide bonds o Primary Structure Protein formation Sequencing of amino acids in polypeptide chain Determines final structure of protein molecule Side chains affect coiling and folding o Secondary Structure Hydrogen bonds Folding of primary structure Provides strength and rigidity helix coiling to form cylindrical shape muscle myosin hair pleated sheet silk protein more flat helix and pleated sheet on same strand o Tertiary Structure Looping and binding of aa s located at considerable distance apart on 2 degrees structure Disulfide bonds provides D dimensions Cys Met o Quaternary Structure Involves two or more polypeptide chains Ex Hemoglobin antibodies o Functional Categories of proteins Enzymes All enzymes are proteins but not all protein are enzymes Hormones Derived from 1 or more aa s Ex insulin 2 polypeptide chains disulfide bridge made in one location and transported in blood stream to location of function o Structural Proteins Contractile proteins muscles Actin myosin Fibrous proteins collagen Cartilage hair bone o Cell Membrane Proteins embedded in cell membrane Membrane channels transporters Glucose transporters Na transporters Receptors LDL receptors Insulin receptors o Plasma Proteins Albumin Synthesized in liver and released into blood Transports nutrients B6 Zn Ca fatty acids Maintains oncotic pressure blood pressure Fluid is attached to albumin which causes higher pressure within vein Protein Digestion and Absorption o Gastric digestion BEGINS IN STOMACH Gastrin HCL Stimulated by food or thought of food Stimulates HCL production Produced by parietal cells Denatures protein Converts pepsinogen pepsin Secreted into lumen of stomach by gastric Zymogens inactive precursor chief cells Pepsinogen Pepsin Autocatalytic activates itself Pepsinogen Pepsin Pepsinogen Cleaves proteins at Leu and aromatic Partial digestion protein polypeptides residues o Stomach not essential for protein digestion Gastrectomy small or no stomach removing of Achlorhydria absence of HCL in gastric juices part of stomach Causes diahyrrea low absorption of protein decreases pepsin SMALL INTESTINES o Duodenal Digestion Chyme enters duodenum Secretin secreted by intestinal mucosa Stimulates pancreatic acinar cell Trypsinogen secretion Stimulates pancreatic bicarbonate Stimulates intestinal production of CCK secreted by mucosa enterokinase A k a Enteropeptidase Trypsinogen enterokinase trypsin Trypsin Activates pancreatic endopeptidase Trypsinogen Trypsin Protelastase Elastase Chymotrypsinogen Chymotrypsin Activates pancreatic exopeptidases Procarboxypeptidase A B Carbosypeptidase A B Enzyme Specificity Each peptidase has a specific cleavage site aliphatic Trypsin able to remove basic AA Elastase removes aliphatics Chymotrypsin removes aromatics Carboxyl A removes aromatic and Carboxyl B removes basic Free amino acids Some di tripeptides Olgiopeptides Digestive products Absorption o Proteins from Digestive enzymes Protein from sloughed mucosal cells o Transport systems Digested and absorbed dietary protein Amino acids absorption Sodium dependent Sodium independent transport systems Specific for groups of amino acids basic Competition for transport Hydrocarbon mass Net electrical charge of amino acid neutral o Rate of amino acid absorption BCAA absorbed quicker than smaller aa s Neutral before basic or acidic Essential before non essential Most slowly are the 2 di carboxylic acidic aa s Ex Glu Asp o Peptides absorption Absorbed more quickly than free aa s After absorption across brush borders o Some aa s stay in intestinal cells and are used for Energy Apoproteins for lipoprotein formation Hormones Metabolized into other a a Digestive enzymes o Shunted to liver via hepatic portal vein Amino Acid Metabolism Decarboxylation o Removal of carboxyl group o Neurotransmitter synthesis Tyrosine dopamine norepinephrine epinephrine Glutamate amino butyric acid GABA Tryptophan serotonin Side Chain Cleavage Deamination o Removal of R chain o Removal amine group Amino acid keto acid NH3 Ex glutamate ketogluterate o Transfer amine group to another molecule Transamination Formation of non essential amino acids Metabolism of keto acids Catalyzed by aminotransferase enzymes Also required B6 as a coenzyme PLP pyridoxal phosphate Transferases as an indicator of liver function o Increases in liver dysfunction results in an increase in transamination reaction requiring ALT AST Alanine amino transferase ALT Aspartate amino transferase AST keto acid carbon skeleton left after N group has been removed Can be used for production of Glucose ketone bodies fatty acids o Energy o Cholesterol o Glucogenic converted to pyruvate and krebs Glucogenic vs Ketogenic intermediates Val His Pro Ala Gly Cys Ser Asp Asn Glu
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