MD140 2122 Macromolecules 1 Proteins Jan 19 2022 PDF

Metabolism, Nutrition and Health Macronutrients Lippincott Illustrated Reviews Biochemistry 7th ed ch 27 Nutrients Ethanol – not an essential nutrient but may provide a significant contribution to the daily caloric intake of some DRI : Dietary Reference Intake Note: Upper level included Daily – refe...

Metabolism, Nutrition and Health Macronutrients Lippincott Illustrated Reviews Biochemistry 7th ed ch 27 Nutrients Ethanol – not an essential nutrient but may provide a significant contribution to the daily caloric intake of some DRI : Dietary Reference Intake Note: Upper level included Daily – refers to average over period of time Function – estimates of nutrients to a) Prevent deficiencies b) Maintain optimal health Protein Functions of Proteins – Multiple (recall Biochem) Functions of Amino Acids- Multiple Nutritionally – goal is to maintain sufficient protein in the diet to replace the amino acids that are degraded Unlike fats and CHO there is a requirement for protein in the diet Growing child – body size increases Adult – continual loss of protein shedding skin cells, enzymes and other proteins secreted into the gut Turnover of tissue protein Mucin in protective mucous throughout the GIT No change in the total amount of protein in adult body An overview of protein metabolism Functions of Amino Acids Glycine  aminolaevulinic acid, a key intermediate in heme synthesis, is made from glycine and succinyl CoA Required for detoxification rxns in liver Principal inhibitory transmitter in the brain stem and spinal cord Occurs at every 3rd aa residue in collagen (the most abundant protein in the body) Tryptophan Precursor of the NT serotonin (5-hydroxytryptamine) Histidine Is decarboxylated to histamine (mmune respnse/physiological function of the gut/neurotransmitter) Arginine Precursor of NO (nitric oxide) Precursor of creatine Lysine Lysine residue interacts with a glutamine when factor X111a converts a low tensile strength fibrin polymer into a high tensile strength clot Multiple functions of AA - Glutamine Substrate for protein synthesis Controls acid-base balance (renal ammoniagenesis) Substrate for hepatic ureagenesis Substrate for hepatic/renal gluconeogenesis Fuel for intestinal enterocytes Ammonia scavenger Substrate for citrulline and arginine synthesis Nitrogen donor (nucleotides, amino sugars, coenzymes Nitrogen transport (1/3 of circulating N) (muscle, lung) Stimulates glycogen syntheses Arginine NO metabolism Meeting Protein and AA needs The 2 major determinants of the nutritional quality of food proteins are The content of the indispensable AAs in the protein The extent to which the indispensable AAs are available to host metabolism Protein and AA Content Traditionally 1st class protein – animal protein 2nd class protein – plant protein - Relates to AA content 1. Quantity 2. Quality: A measure of its ability to provide the essential amino acids required for tissue maintenance. PDCAAS – standard by which to evaluate protein quality. Based on (i) profile of AAs (ii) digestibility of the protein PDCAAS: Protein Digestibility-Corrected amino acid scoring Tot Def in tryptophan, also def in isoleucine, threonine Def -Met: Rich - Lys Def -lys: Rich - Met Relative Quality of Some Common Dietary Proteins Wheat - lysine deficient, methionine rich + Beans - Methionine poor but lysine rich Nitrogen Balance +ive = intake > excreted : tissue growth -ive = loss > intake: inadequate dietary protein, lack of an essential aa, during physiologic stress e.g trauma, burns, illness or surgery Protein losses in trauma and infection Tissue Loss Blood Loss Catabolism TOTAL (g) Fracture of Femur - 200 700 900 Muscle Wound 500-750 150-400 750 1350-1900 35% burns 500 150-400 750 1400-1650 Gastrectomy 20-180 20-100 625-750 645-850 Typhoid Fever - 675 685 Requirements Approx 0.8g/kg of body weight for adults Athletes = approx 1.0g/kg Pregnant/lactating women = 30g/day Children = 2g/kg/day Protein-Energy Malnutrition- PEM Adequate protein & Health Pure Protein deficiency: Kwashiorkor – typically a disease of children Energy Deficiency: Maramus Reduced number of T lymphocytes (diminished cell-mediated immune response) Defects in generation of phagocytic cells and production of Immunoglobulins, interferons and other components of the immune system Many die from secondary infection rather than starvation PEM The most common form of PEM in the US occurs in hospitals Normal response to infection, trauma and surgery – carefully balanced catabolic state Glucocorticoids, interleukin-6 and other cytokines released Accelerated rate of lipolysis, proteolysis and gluconeogenesis Net result is reflected by low serum albumin or decreased cellular immunity Xs Protein Increased protein intake results in increased protein-breakdown products e.g. Urea Urea needs to be eliminated by the kidneys High protein diets increase water loss Causes problem if kidneys cannot concentrate urine Immature kidneys of infants cannot concentrate urine - Excrete xs fluid - Causes dehydration - Also a risk for those with kidney disease AAs with similar structures compete for absorption Use same transport systems Xs of one will slow adsorption of another Concern when people use supplements e.g. weight lifters often take supplements of arginine - Shares with lysine - Upset aa balance in the body Absorption of Protein fragments can cause allergies Food allergies are triggered when a protein from the diet is absorbed without being completely digested Many factors contribute to the overall allergenicity of any given protein Essential and Non-Essential Amino Acids ESSENTIAL ESSENTIAL PRECURSOR NON-ESSENTIAL Semi-essential Histidine Alanine Arginine Isoleucine Aspartate Asparagine Leucine Glutamate Glutamine Lysine Glycine Methionine Cysteine Proline Phenylalanine Tyrosine Serine Threonine Tryptophan Valine Alanine from Pyruvate Aspartate from Oxaloacetate 9 essential Glutamate from -KG Infants - arginine is also essential Cysteine from methionine and tyrosine from phenylalanine