Multipurpose molecules Proteins Multipurpose molecules clockwise: Rubisco — most important protein on the planet? Hemoglobin — a red blooded protein :-) Collagen — strings you together Growth Hormones — working hard in you right now! 2006-2007

Proteins Most structurally & functionally diverse group of biomolecules Function: involved in almost everything enzymes (pepsin, polymerase, etc.) structure (keratin, collagen) carriers & transport (membrane channels) receptors & binding (defense: antibodies) contraction (actin & myosin) signaling (hormones: insulin) storage (bean seed proteins) Storage: beans (seed proteins) Movement: muscle fibers Cell surface proteins: labels that ID cell as self vs. foreign Antibodies: recognize the labels ENZYMES!!!!

Proteins Structure: monomer = amino acids polymer = polypeptide 20 different amino acids polymer = polypeptide protein can be one or more polypeptide chains folded & bonded together complex 3-D shape hemoglobin Rubisco growth hormones

In Biology, size doesn’t matter, Denature a protein In Biology, size doesn’t matter, SHAPE matters! Unfolding a protein disrupt 3° structure pH  salt  temperature unravels or denatures protein disrupts H bonds, ionic bonds & disulfide bridges destroys functionality Some proteins can return to their functional shape after denaturation, many cannot Example: Eggs: Cooking an egg permanently denatures the proteins.

Amino acids H O | H || —C— C—OH —N— R Structure: central carbon amino group carboxyl group (acid) R group (side chain) variable group confers unique chemical properties of the amino acid | —C— H C—OH || O —N— H R

Why are these nonpolar & hydrophobic? Nonpolar amino acids nonpolar & hydrophobic Why are these nonpolar & hydrophobic?

Why are these polar & hydrophillic? Polar amino acids Polar/charged & hydrophilic Why are these polar & hydrophillic?

Sulfur containing amino acids Form disulfide bridges cross links betweens sulfurs in amino acids H-S – S-H

dehydration synthesis Building proteins Peptide bonds linking NH2 of one amino acid to COOH of another C–N bond dehydration synthesis free COOH group on one end is ready to form another peptide bond so they “grow” in one direction from N-terminal to C-terminal peptide bond

Building proteins Polypeptide chains N-terminus = NH2 end C-terminus = COOH end repeated sequence (N-C-C) is the polypeptide backbone can only grow in one direction

Primary (1°) structure Order of amino acids in chain determined by gene (DNA) sequence can affect protein’s structure & function Sickle cell anemia: 1 DNA letter changes 1 amino acid = serious disease Hemoglobin mutation: bends red blood cells out of shape & they clog your veins. lysozyme: enzyme in tears & mucus that kills bacteria

Secondary (2°) structure “Local folding” interaction between adjacent amino acids H bonds between R groups -helix -pleated sheet It’s a helix or B sheet within a single region. Can have both in one protein but a specific region is one or another

Tertiary (3°) structure “Whole molecule folding” determined by interactions between R groups hydrophobic interactions water in cell anchored by disulfide bridges (H & ionic bonds) How the whole thing holds together

Quaternary (4°) structure More than one polypeptide chain joined together only then is it a functional protein Structure equals function wonderfully illustrated by proteins Collagen is just like rope -- enables your skin to be strong and flexible. hemoglobin collagen = skin & tendons

Protein structure (review) R groups hydrophobic interactions, disulfide bridges 3° multiple polypeptides hydrophobic interactions sequence determines structure and… structure determines function. Change the sequence & that changes the structure which changes the function. 1° aa sequence peptide bonds 2° determined by DNA R groups H bonds 4°