Metab 1 Proteins 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 I Amino Acids Structure II Structural Classification A Aliphatic Side Chains 5 B Side Chains with OH group 2 C Side Chains with Sulfur 2 D Side Chains with carboxyl or amide groups 4 E Side Chains with basic groups 3 F Side Chains with aromatic rings 3 G Imino acid DIETARY PROTEIN Exogenous Protein I Quality A Digestibility 1 Animal proteins 90 99 2 Plant sources 70 90 lower because of fiber content B Amino Acid composition 1 Complete Protein a Contains all essential amino acids b All animal sources c Exceptions gelatin no tryptophan and soy plant 2 Incomplete Protein a Low in one or more amino acids b Examples Beans low in methionine Rice low in lysine Whatever AA the food is low in is known as the limiting amino acid a 2 or more proteins when combined provide all essential 3 Complementary amino acids b Examples Beans and rice Lentil soup with cornbread II Requirements A EAR estimated average requirement 0 66 g kg day 1 Lowest amount to maintain nitrogen balance of 0 in average 2 Based on a reference protein highly digestible and healthy adult complete B RDA recommended dietary allowance 0 8 g kg day 1 2 SD covers 98 of healthy populations C Special Needs general guidelines in order 1 Adolescents LOWEST 0 8 2 g kg 2 Children 3 4 Pregnancy 5 Lactation HIGHEST 15 g kg Infants Infants 0 1yr Children 4 8 Adolescents 14 18 Pregnancy Lactation Surgery Burns g day 11 9 1 19 46 52 25 25 g kg day 1 2 1 52 0 95 0 85 1 1 1 1 1 2 1 4 1 6 2 0 Renal insufficiency 0 6 0 8 Clinical Issues Branched chain amino acids often used in supplements for those with decreased liver function HN formulas high nitrogen to promote healing in those with low intake Enteral goes through the gut Parenteral through IV to get nutrients D Calculating protein requirements 1 kg 2 2 lbs Protein contributes 10 30 of total kcal 1 g Protein 4 kcal A healthy adult female weighing 125 lbs consumes approximately 50 g of protein a day 1 How many g kg is she consuming 50g 125lb 1kg 2 2lbs 125lbs 56 818 kg 50g 56 818kg 0 88 g kg 2 How many g of nitrogen is she consuming 0 16g nitrogen 1g protein 50g protein 8g nitrogen 3 How many calories does protein contribute 4 kcal 1g protein 50g protein 200 kcal 4 If she consumes 2000 kcal what percentage of that is protein 200kcal of protein 2000 total kcal 0 1 10 E Can we get too much protein 1 Amino acids urea excreted by kidneys 2 High protein diet should be avoided if a Kidney disease b Have only 1 kidney or decreased kidney function c Infants ie Cows milk protein content and mineral content too high should drink breast milk because it has less protein than whole milk 3 keto acid from metabolized amino acid a Transamination Converted to ATP Stored as fat 4 Amino acid supplements a Transporters on intestinal cells b 11 transporters for 20 amino acids c Competition for transporters d Not a problem when consuming whole proteins e Amino acid supplements limit absorption of whole f proteins Some amino acid supplements have been found to be contaminated Tryptophan i Claims sleep mood enhancement autism pain tolerance appetite control chemical addictions jet lag ii NOT FDA APPROVED iii Contamination caused Eosinophilia myalgia death F Too little protein 1 Protein needed for a Hair b Skin c Bones d Muscle e Tendons f Enzymes g Membranes h Oncotic pressure i Acid base balance 2 Protein Energy Malnutrition 1 Kwashiorkor enough energy kcal normal low protein Acute PEM protein energy malnutrition Older infants and children Edema Fatty liver carbs are eaten and turned into fat lipoproteins are not present to carry fat out of liver 2 Marasmus low in calories and protein no body fat Severe deprivation Chronic PEM protein energy malnutrition Muscle wasting No body fat No edema No fatty liver Can be seen in people who have been anorexic or elderly population who can t eat as much or forget to eat 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 Denatures protein 3 Converts pepsinogen pepsin C Pepsinogen 1 Secreted into the lumen of stomach by gastric chief cells 2 Zymogen inactive precursor D Pepsin 1 Autocatalytic activates itself HCL 2 Cleaves proteins at Leu and aromatic residues Phenylalanine Tyrosine Tryptophan 3 Partial digestion of protein polypeptides II Duodenal Digestion A Chyme enters duodenum B Secretin secreted by intestinal mucosa 1 Stimulates pancreatic acinar cells 2 Trypsinogen secretion C CCK secreted by mucosa 1 Stimulates pancreatic bicarbonate 2 Stimulates intestinal production of enterokinase aka Enteropeptidase Enterokinase Trypsinogen Trypsin D Trypsin 1 Activates pancreatic endopeptidases a Trypsinogen Trypsin b Protelastase Elastase c Chymotrypsinogen Chymotrypsin 2 Activates pancreatic exopeptidases Procarboxypeptidase A B Carboxypeptidase A B E Enzyme Specificity 1 Each peptidase has a specific cleavage site a Trypsin basic amino acid b Elastase aliphatics c Chymotrypsin aromatics cleaves in middle d Carboxy A aromatic and aliphatic cleaves at end e Carboxy B basic 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 3 Digestive enzymes 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 i Hydrocarbon mass ii Net electrical charge of amino acid Amino Acid Transport System Examples of Substrates Carried L y ba t X A AG ASC asc GLY Leucine other neutral amino acids Basic amino acids Neutral and basic amino acids Phenylalanine tyrosine tryptophan Aspartate and glutamate Alanine other short chain polar neutral amino acids Alanine cysteine serine other three and four carbon amino acids Same substrates as ASC Glycine C Rate of amino acid absorption 1 BCAA absorbed quicker than smaller amino acids 2 Neutral before basic or acidic 3 Essential before non essential 4 Most slowly are the 2 dicarboxylic acidic amino acids Glu and Asp D Peptides absorption 1 Absorbed more quickly than free amino acids IV After absorption across brush border A Some amino acids stay in intestinal cells and are used for 1 Digestive enzymes 2 Apoproteins for
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