4. Protein Digestion and Metabolism.pdf

HNUT10010 HNUT10020 Human Nutrition 1: Understanding Nutrients Aifric O’Sullivan BSc, MSc, PhD UCD Institute of Food and Health School of Agriculture and Food Science Protein Digestion and Metabolism • Protein digestion • Protein absorption • Protein metabolism Protein Digestion Peptidases Ca...

HNUT10010 HNUT10020 Human Nutrition 1: Understanding Nutrients Aifric O’Sullivan BSc, MSc, PhD UCD Institute of Food and Health School of Agriculture and Food Science Protein Digestion and Metabolism • Protein digestion • Protein absorption • Protein metabolism Protein Digestion Peptidases Carboxypeptidase A Targets neutral nonpolar Exopeptidase Carboxypeptidase A Trypsin Targets basic AA Endopeptidase Chymotrypsin Targets aromatic AA Endopeptidase Protein Absorption • • • • • Several brush boarder AA transporters Some sodium dependent/some not Dipeptides and tripeptides PEPT1 (H+) Faster than AA  hydrolysed within cell Several basolateral membrane AA transporters Protein Absorption • Transporter affinity for an AA depends on: Side chain (size, charge) • Larger are quicker • Neutral are quicker Indispensable • Met, leu, ile, val quickest • Glutamate and aspartate slowest Protein Metabolism • Catabolism: deamination and transamination Energy, glucose, ketones, cholesterol fat, dispensable AA Alanine → glutamate Deamination • Take away nitrogen containing amino group • Left with ammonia (NH3) and keto acid • Keto acid can be used for energy, glucose, ketones, cholesterol or fat or non-essential AA Transamination • Amino group is transferred from an amino acid to a keto acid to form a new amino acid glutamate + pyruvate ⇌ α-ketoglutarate + alanine Urea Synthesis • Ammonia excretion • Liver and kidney • High protein diet Quiz • On a scale of 1 to 5, how difficult was this lecture? • What slides were most difficult? 11 References • WHO/FAO/UNU Expert Consultation. Protein and Amino Acid Requirements in Human Nutrition: report of a joint FAO/WHO/UNU expert consultation. WHO Technical Report Series. Geneva, 2007. Available: http://whqlibdoc.who.int/trs/WHO_TRS_935_eng.pdf • Gibney M, Lanham-New S, Cassidy A, Vorster H, eds. Introduction to Human Nutrition. 2nd ed: Wiley-Blackwell, 2009. Chapter 4 • Biolo G, Maggi SP, Williams BD, Tipton KD, Wolfe RR. Increased rates of muscle protein turnover and amino acid transport after resistance exercise in humans. Am J Physiol 1995;268:E514-20