Proteins Introduction to Proteins Made up of amino acids Functions Growth and maintenance Enzymes Hormones Fluid balance Acid base balance Transportation Antibodies Energy I Amino Acids structure H3N CH COO R 1 II Structural Classification A Aliphatic Side Chains 5 B Side Chains with OH group 2 C Side Chains with sulfer 2 2 D Side Chains with carboxyl or amide groups 4 E Side chains with basic groups 3 F Side chains with aromatic rings 3 3 G Imino acid Dietary Protein Exogenous Protein I Quality A Digestibility 1 Animal proteins 2 Plant sources B Amino Acid composition 4 1 Complete protein a b all animal sources c exceptions 2 Incomplete protein a b examples beans low in methionine rice low in lysine 3 complementary proteins a ex beans and rice lentil soup with cornbread II Requirements A EAR 1 Lowest amount to maintain nitrogen balance of 0 in average healthy adult 2 Based on a reference protein B RDA recommended dietary allowance 0 8g kg day 1 2 SD 5 C Special Needs general guidelines infants children adolescents pregnancy lactation Special Needs continued Clinical Issues BCAA s often used in supplements HN formulas high nitrogen D Calculating protein requirements 1 kg 2 2 lbs Protein contributes 10 30 of total kcal 1 g Pro 4 kcal A healthy adult female weighing 125 lbs consumes approximately 50g of protein a day 1 How many g kg is she consuming 2 How many g of nitrogen is she consuming 3 How many calories does protein contribute 4 If she consumes 2000 kcal what percentage of that is protein 6 E Can we get too much protein 1 Amino acids urea 2 High protein diet should be avoided if a kidney disease b have only 1 kidney or decreased kidney function 3 keto acid from metabolized amino acid 4 Amino acid supplements a transporters on intestinal cells b 11 transporters for 20 amino acids c competition for transporters d f some aa supplements have been found to be contaminated a tryptophan F Too little protein 1 Protein needed for skin tendons hair muscle membranes acid base balance bones enzymes oncotic pressure 2 Protein Energy Malnutrition 1 Kwashiorkor 2 Marasmus 7 Protein Digestion and Absorption I Gastric digestion A Gastrin 1 stimulated by food or thought 2 stimulates HCL production B HCL 1 produced by parietal cells 2 3 converts pepsinogen pepsin C Pepsinogen 1 secreted into the lumen of stomach by gastric chief cells 2 Zymogen Pepsinogen HCL Pepsin 8 D Pepsin 1 Autocatalytic activates itself pepsinogen pepsin 2 Cleaves proteins at Leu and aromatic residues 3 Partial digestion protein II Duodenal Digestion A Chyme enters duodenum B Secretin secreted by intestinal mucosa 1 stimulates pancreatic acinar cells 2 C CCK secreted by mucosa 1 stimulates pancreatic bicarbonate 2 stimulates intestinal production of enterokinase aka Enteropeptidase D Trypsin 1 activates pancreatic endopeptidases a Trypsinogen b Protelastase c Chymotrypsinogen 2 activates pancreatic exopeptidases Procarboxypeptidase A B 9 E Enzyme Specificity 1 Each peptidase has a specific cleavage site a Trypsin b Elastase c Chymotrypsin d Carboxy A e Carboxy B 2 Digestive products a Free amino acids b Some di tripeptides c oligopeptides III Absorption A Proteins from 1 digested and absorbed dietary protein 2 protein from sloughed mucosal cells B Transport systems 1 Amino acid absorption a sodium dependent b sodium independent transport systems c specific for groups of amino acids basic neutral d competition for transport 1 hydrocarbon mass 2 net electrical charge of amino acid 10 C Rate of amino acid absorption 1 BCAA absorbed quicker than smaller aa s 2 neutral before basic or acidic 3 4 most slowly are the 2 dicarboxylic acidic aa s glu and asp D Peptides absorption IV After absorption across brush border A Some aa s stay in intestinal cells and are used for 1 digestive enzymes 2 apoproteins for lipoprotein formation 3 B Shunted to liver via hepatic portal vein 11
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