3. Amino Acid and Protein Biochemistry.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 Amino Acid and Protein Biochemistry • • • • Amino acid structure Classification based on side chain (R-group) Protein synthesis P...

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 Amino Acid and Protein Biochemistry • • • • Amino acid structure Classification based on side chain (R-group) Protein synthesis Protein structure Amino Acids: Building Blocks 1. 2. 3. 4. Central carbon bonded to a hydrogen Nitrogen containing amino group A carboxyl group Side group varies Amino Acids: Building Blocks 1. 2. 3. 4. Chiral compounds L-amino acids Positive or negative charge depending on pH At neutral pH the amino group has a positive charge (NH3+) and the carboxyl group has a negative charge (COO-) so it is neutral 5. The side group makes each unique Amino Acids: Building Blocks Classification • Chemical structure similarities (side group) – Charged or neutral – Polar or non-polar • Nutrition – Dispensable – Indispensable – Conditionally indispensable Amino Acids: Building Blocks • • • • Side-group determines functional differences Different sizes Neutral, positive or negative charge Polar or non-polar (interaction with water) Neutral Polar: hydroxyl, sulfur, amide group Non-polar: aliphatic side chain Relatively non-polar: aromatic ring , , Acidic (negative): carboxyl group in side chain Basic (positive): amino group in side chain Classified as polar charged , Amino Acids: Building Blocks • Polarity and charge can impact the position of the amino acid within a protein and the folding of a protein • Attractions between positive and negative charges pull different parts of the molecule together • Hydrophobic (non-polar) groups tend to cluster together in the centre of proteins • Hydrophilic (polar) groups remain on the outside • The sulfur containing groups of cysteine form disulfide bonds which is important in folding and in the formation of inter-polypeptide bonds How Are Proteins Made? 1 2 3 1. Information contained in DNA is transcribed to form mRNA 2. mRNA moves to the cytoplasm where it attaches to the ribosome © Cenage Learning Protein Synthesis 4 • tRNA transport amino acids to the ribosome in the correct sequence • Amino acids are joined by peptide bonds • When translation is complete the peptide separates from the ribosome 5 6 How Do Proteins Get Their Shape? Primary sequence of amino acids, basic identity Secondary 3D shape, folding portions of the chain Tertiary 3D shape, additional folding Quaternary 2 or more polypeptides come together Primary Structure • Sequence of amino acids in a polypeptide • Determines most basic characteristics • Sequence influences the 3D folding Secondary Structure -Helix • Clockwise coil • 3.5 AA per turn • Stabilised by H bonds • R groups point out β-sheet • Polypeptide side by side • R groups alternate – above and below • Stabilised by H bonds Tertiary Structure • Describes the more complex 3D structure • Additional folding due to interactions of side chains 4. Quaternary Structure Only proteins made from more than one polypeptide Quiz • On a scale of 1 to 5, how difficult was this lecture? • What slides were most difficult? 16 Reading • Gibney M, Lanham-New S, Cassidy A, Vorster H, eds. Introduction to Human Nutrition. 2nd ed: WileyBlackwell, 2009. Chapter 4 • Campbell MK, Farrell SO. Biochemistry, International Edition, 7th Edition. Singapore: CENGAGE Learning, 2012. Chapters 3 & 4 • McGuire M, Beerman KA: Nutritional Sciences: From Fundamentals to Food. 3rd ed. Belmont, CA: Wadsworth; 2013. Chapter 5