HUN3224 Introduction to proteins o Made up of amino acids o Functions Metabolism of Proteins Enzymes Growth and maintenance Hormones Fluid balance Acid base balance Transportation Antibodies Energy Structural elements Structural classifications o Aliphatic open side chains Gly Ala Val Ile Leu o Side chains with OH Thr Ser o Side chains with sulfur Met Cys o Side chains with carboxylic or amine groups Asp Glu Asn Gln o Side chains with basic groups o Side chains with aromatic rings Lys Arg His Tyr Trp Phe o Imino acid Pro Exogenous dietary protein o Digestibility Animal proteins 90 99 Plant sources 70 90 o Complete v incomplete RDA 0 8g kg d Incomplete is missing 1 or more amino acid Complete proteins all animal sources except gelatin soy plant source but still complete Incomplete ex beans low in methionine and rice low in lysine Complementary proteins 2 or more proteins that when combined provide all essential amino acids Branched Chain amino acids often used in supplements for those with decreased liver function o Arginine promote wound healing collagen synthesis o Glutamine enteral formulas induces protective responses in gut HUN3224 Special Needs o Infants 1 2 1 52 g kg d o Children 0 95 g kg d o Adolescents 0 85 g kg d o Pregnancy and lactation 1 1 g kg d o Surgery and burns 1 6 2 00 g kg d o Renal 0 6 0 8 g kg d Can we get too much protein o Amino acids urea excreted by kidneys High protein diet should be avoided if o Kidney disease o Have only 1 kidney or decreased kidney function o Infants Amino acid supplements o 11 transports for 20 amino acids o Competition for transporters o AA supplements limit absorption of whole proteins o Trp found to be contaminated Protein needed for hair muscle skin etc Protein Energy Malnutrition PEM o Kwashiorkor Kcal normal low protein Acute PEM fatty liver no protein present to transfer fat stores out of liver o Marasmus Low in Kcal low in protein Severe deprivation chronic PEM Muscle wasting no body fat no edema no fatty liver long term starvation Protein digestion and absorption o Really begins in the stomach o Gastric digestion Gastrin stimulated by food or thought Stimulates HCl production HCl Produced by parietal cells Denatures protein except primary structure cannot break peptide bonds Converts pepsinogen to pepsin Pepsinogen Secreted into the lumen of the stomach by gastric chief cell HUN3224 Zymogen active precursor Pepsin Autocatalytic Hydrolyzes peptide bonds in proteins Cleaves proteins at Leu and aromatic residues ONLY these specific amino acids Stomach is not essential for protein digestion Achlorhydria absence of HCl in gastric juices o Duodenal digestion Chyme enters duodenum Secretin secreted by intestinal mucosa Stimulates pancreatic acinar cells Trypsinogen secretion CCK stimulated by mucosa Stimulates pancreatic bicarbonate Stimulates intestinal production of enterokinase activates trypsin which activates other pancreatic zymogens Activates pancreatic enteropeptidases cleave peptide bonds in middle Trypsin o Trypsinogen Trypsin o Proelastase Elastase o Chymotrypsinogen chymotrypsin Activates exopeptidases cleave peptide bonds at end o Procarboxypeptidase A and B Carboxypeptidase A and B Zinc dependent Enzyme specificity Each peptidase has a specific cleavage site o Trypsin basic amino acids o Elastase aliphatics o Chymotrypsin aromatics o Carboxy A aromatic or aliphatic o Carboxy B basic amino acids Digestive products amino acids some di and tri peptidases oligopeptides o Absorption Transport systems Amino acid absorption o Sodium dependent o Specific for groups of amino acids basic neutral etc o Competition for transport Hydrocarbon mass Net electrical charge of amino acids HUN3224 Rate of amino acid absorption o Branched chain amino acids BCAA absorbed quicker than smaller amino acids o Neutral absorbed before basic or acidic o Essential absorbed before nonessential o Peptides absorbed more quickly than free amino acids o Absorption across brush border Some amino acids stay in intestinal cells and are used for Apoproteins for lipoprotein formation Digestive enzymes Hormones Metabolized into other amino acids Shunted to liver via hepatic portal vein Phe Val Thr Trp Ile Met Leu Lys Conditionally essential Cys Tyr o Essential v nonessential amino acids Essential cannot be synthesized by the body must be consumed from diet If a protein requires an essential amino acid and the body does not have it protein synthesis will halt o Protein formation DNA RNA via transcription proteins via translation Exons coding regions Introns noncoding region mRNA is made from exons RNA mRNA tRNA rRNA o copy of blueprint that can leave nucleus o reads mRNA and binds to corresponding amino acid o protein synthesizing machinery o Proteins undergo post translational modifications including adding nutrients to become active proteins o Primary structure sequence of amino acids in polypeptide chain Determined by DNA o Secondary structure Folding of primary structure H bonding Alpha helix and beta sheet Interaction between main chain o Zwitter ion amino acids with no carboxy or amine groups in their side chain to generate HUN3224 o Tertiary structure Looping and binding of amino acids i e disulfide bonds interaction between side chains o Quaternary structure Involves two or more polypeptide chains i e hemoglobin additional charge on the molecule Functional categories of proteins o Enzymes o Hormones o Structural Contractile muscle Actin myosin Fibrous Cartilage hair bone Cell membrane proteins Plasma proteins o Albumin Mutations o Point mutation at a single base o Gene rearrangements o Frame shift mutations o Gene deletions duplications Nutrient related mutations o Cystic fibrosis Transports nutrients B6 zinc calcium fatty acids Maintains oncotic pressure Body produces unusually sticky thick mucus o Wilson s disease copper overloading o Acrodermatitis enteropathica trouble allowing zinc into body o Hemochromatosis o Vitamin D Resistant Rickets Genetic mutation in the Vitamin D receptor that alters its function o Maple Syrup Urine Disease Results in deficiency of 1 of the 6 proteins that make up the branched chain keto dehydrogenase complex o Carbamoyl Phosphate Synthase Deficiency o Phenylketonuria Amino Acid Metabolism HUN3224 o Decarboxylation Removal or carboxyl group Neurotransmitter synthesis Tyrosine dopamine epinephrine norepinephrine Glutamate GABA Tryptophan serotonin o Side chain cleavage Removal of R chain Not very often o Deamination o
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