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The Macronutrients-Proteins Chapter 1 Overview of Protein • Body is made up of thousands of protein substances – More than 30,000 different kinds of protein – Unique structure and function – Twenty amino acids commonly found in human protein – Proteins = 50% of the dry weight of most cells Overview of Protein • Made up of amino acids • Contains carbon, hydrogen, and oxygen – And at least one N in structures • N is in the form of an amine group (NH2) – Carboxyl group (COOH) – R group: side chain, this is what makes each amino acid unique Amino Acid R NH2 O C C OH H R group Acid group Nitrogen group Overview of Proteins • Amino acids – Peptide bonds – Dipeptide – two amino acids – Tripeptide – three amino acids – Polypeptides – multiple amino acids Protein Organization • Polypeptide chain – Twists and bends to native conformation – Determined by side chains • Hydrophilic – outer surface • Hyrophobic - folded inside Proteins • Order of amino acids – Determines shape • Final shape – Determines function – Determines stability Fig. 02.16a Proteins • Denaturation – Uncoiling – alters function • Heat • Stomach acid • Irreversible Denaturation of Proteins Denaturation • Foods are a means of obtaining amino acids • Cooking can make substances available – Vitamin – biotin (cooked eggs) Denaturation of Proteins Heat/acid/alkaline/enzymes Results in alteration of the protein’s three dimensional structure Overview of Protein • Amino acids-20 required by body – Essential – indispensable • Body does not have pathway to synthesize • Supplied by diet – Non-essential • Can be provided through metabolic pathways – Conditionally essential amino acids • Under certain conditions • Typically malnutrition Dietary Protein • Animal proteins – High-quality – Complete – 8 essential amino acids • Low-quality – Incomplete • Lacks one or more essential amino acids – Most plant foods – Cannot meet all amino acid needs – Greater variety and amount of plant proteins needed Transamination • Transfer of an amine group – From a donor amino acid – To an acceptor amino acid • Formation of new amino acid Dietary Protein • All-or-none principle in protein synthesis – If not all of the amino acids are present, protein synthesis does not occur • Limiting amino acids – Essential amino acid in smallest supply • Complementary proteins – Mixed diets – foods containing different amino acids are combined Limiting Amino Acid C is the limiting amino acid in this example CCCCC AAAAAAAA RRRRRR CAR CAR CAR CAR CAR R A A A Complementary Protein Food 1 Food 2 CC AAAA RRR CCCC AA RRR Combined CAR CAR CAR CAR CAR CAR Vegetarians • Protein requirements – Variety of plant foods - Complementary • Grains and legumes • Soy protein – Lacto vegetarian • Milk, milk products – Ovolactovegetarian • Eggs Protein • • • • • • Sedentary Recreational exercisers Serious RT, early Serious RT, established Serious endurance Adolescent athlete 0.8-1.0 g/kg/d 0.8-1.0 1.5-1.7 1.0-1.2 1.2-1.6 1.5-2.0 Role of Proteins • Protein content of skeletal muscle – 65% total protein of body • Component of tissue structures – Cells – RNA, DNA – Electron carriers • NAD, FAD Structural Proteins Structural Proteins Globular Proteins Protein Turnover • Replenishment of protein containing structures – Amino acid pool • Anabolism – Tissue building • Catabolism – Tissue breakdown Nitrogen Balance • Positive nitrogen balance – Intake exceeds excretion • Synthesis of new tissues • Negative nitrogen balance – Protein used for energy – Uses reserves – skeletal muscle Protein Metabolism • Deamination – Releases amine group – Urea • Fate of deaminated carbon compound – Make new aa – Converted to CHO or fat – Catabolized for energy Additional Roles of Protein • Nervous and connective tissue – Not in energy metabolism • Alanine provides CHO fuel – Gluconeogenesis – prolonged exercise • Alanine-glucose cycle provides 40-50% – From liver’s glucose release – Provide up to 15% of the total energy requirement