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Chapter 3 Proteins You Must Know • How the sequence and subcomponents of proteins determine their properties. • The cellular functions of proteins. (Brief – we will come back to this in other chapters.) • The four structural levels of proteins and how changes at any level can affect the activity of the protein. • How proteins reach their final shape (conformation), the denaturing impact that heat and pH can have on protein structure, and how these may affect the organism. • The directionality of proteins (the amino and carboxyl ends). Concept 3.5: Proteins include a diversity of structures, resulting in a wide range of functions • Proteins account for more than 50% of the dry mass of most cells. • Protein functions include defense, storage, transport, cellular communication, movement, and structural support. © 2014 Pearson Education, Inc. • Life would not be possible without enzymes. • Enzymatic proteins act as catalysts, to speed up chemical reactions without being consumed by the reaction Enzyme © 2014 Pearson Education, Inc. • Polypeptides are unbranched polymers built from the same set of 20 amino acids • A protein is a biologically functional molecule that consists of one or more polypeptides © 2014 Pearson Education, Inc. Figure 3.UN04 Amino Acids: the monomers of proteins Side chain (R group) carbon Amino group Carboxyl group Figure 3.17a What do the side chains of these amino acids have in common? Side chain (R group) Glycine (Gly or G) Methionine (Met or M) Alanine (Ala or A) Valine (Val or V) Phenylalanine (Phe or F) Leucine (Leu or L) Tryptophan (Trp or W) Isoleucine (le or ) Proline (Pro or P) Figure 3.17b What do the side chains of these amino acids have in common? Serine (Ser or S) Threonine (Thr or T) Cysteine (Cys or C) Tyrosine (Tyr or Y) Asparagine (Asn or N) Glutamine (Gln or Q) Figure 3.17c What do the side chains of these amino acids have in common? Aspartic acid (Asp or D) Glutamic acid (Glu or E) Figure 3.17c What do the side chains of these amino acids have in common? Lysine (Lys or K) Arginine (Arg or R) Histidine (His or H) You don’t need to memorize all the different side chains of the amino acids, but when shown a side chain you should be able to identify its properties (e.g. polar, ionized, etc.) N-terminus peptide bond C-terminus Protein Structure and Function • A functional protein consists of one or more polypeptides precisely twisted, folded, and coiled into a unique shape. A protein’s structure determines its function! Hemoglobin protein © 2014 Pearson Education, Inc. How does an organism “know” what proteins to make? • DNA dictates the sequence of amino acids. • The sequence of amino acids leads to the protein’s three-dimensional structure. Four Levels of Protein Structure • Proteins are very diverse, but share three superimposed levels of structure called primary, secondary, and tertiary structure. • A fourth level, quaternary structure, arises when a protein consists of more than one polypeptide chain © 2014 Pearson Education, Inc. Figure 3.21a Primary structure Amino acids 1 10 5 Amino end 30 35 15 20 25 45 40 50 Primary structure of transthyretin 65 70 55 60 75 80 90 85 95 115 120 110 105 100 125 Carboxyl end Figure 3.21ba Secondary structure helix pleated sheet Hydrogen bond strand Hydrogen bond Figure 3.21d Tertiary structure Hydrogen bond Hydrophobic interactions and van der Waals interactions Disulfide bridge Ionic bond Polypeptide backbone Figure 3.21f Quaternary Structure Heme Iron subunit subunit subunit subunit Hemoglobin “mad cow disease” Figure 3.23-1 Normal protein Figure 3.23-2 Normal protein Denatured protein Figure 3.23-3 Normal protein Denatured protein