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 © 2014 Pearson Education, Inc. Enzyme

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 Side chain (R group) Carboxyl group Amino group  carbon Amino Acids

Figure 3.17a What do the side chains of these amino acids have in common? Side chain (R group) Glycine (Gly or G) Alanine (Ala or A) Methionine (Met or M) Phenylalanine (Phe or F) Leucine (Leu or L) Isoleucine (  le or  ) Tryptophan (Trp or W) Proline (Pro or P) Valine (Val or V)

Figure 3.17b Serine (Ser or S) Threonine (Thr or T) Tyrosine (Tyr or Y) Asparagine (Asn or N) Cysteine (Cys or C) Glutamine (Gln or Q) What do the side chains of these amino acids have in common?

Figure 3.17c Aspartic acid (Asp or D) Glutamic acid (Glu or E) What do the side chains of these amino acids have in common?

Figure 3.17c Arginine (Arg or R) Lysine (Lys or K) Histidine (His or H) What do the side chains of these amino acids have in common?

C-terminus N-terminus peptide bond

Protein Structure and Function A functional protein consists of one or more polypeptides precisely twisted, folded, and coiled into a unique shape © 2014 Pearson Education, Inc.

“mad cow disease”

The sequence of amino acids, determined genetically, leads to a protein’s three-dimensional structure. A protein’s structure determines its function © 2014 Pearson Education, Inc.

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 end Carboxyl end Primary structure of transthyretin Amino acids

Figure 3.21ba Secondary structure Hydrogen bond  pleated sheet  helix Hydrogen bond  strand

Figure 3.21d Polypeptide backbone Hydrogen bond Disulfide bridge Ionic bond Hydrophobic interactions and van der Waals interactions Tertiary structure

Figure 3.21f Heme Iron  subunit  subunit Hemoglobin Quaternary Structure

Figure Normal protein

Figure Normal protein Denatured protein

Figure Denatured protein Normal protein