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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)
Proteins • Structure: • monomer =amino acids • 20 different amino acids • polymer =polypeptide • protein can be one or more polypeptide chains folded & bonded together • large & complex molecules • complex 3-D shape hemoglobin growthhormones Rubisco
H O | —C— | H || C—OH —N— H Amino acids • Structure: • central carbon • amino group • carboxyl group (acid) • R group (side chain) • variable group • confers unique chemical properties of the amino acid R
nonpolar & hydrophobic Nonpolar amino acids Why are these nonpolar & hydrophobic?
polar or charged & hydrophilic Polar amino acids Why are these polar & hydrophillic?
Sulfur containing amino acids • Formdisulfide bridges • cross links betweens sulfurs in amino acids H-S – S-H You wonderedwhy permssmelled like rotten eggs?
peptidebond Building proteins • Peptide bonds • linking NH2 of one amino acid to COOH of another • C–N bond dehydration synthesis
Protein models • Protein structure visualized by • X-ray crystallography • extrapolating from amino acid sequence • computer modelling lysozyme
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
hemoglobin collagen Protein structure & function • Function depends on structure • 3-D structure • twisted, folded, coiled into unique shape pepsin
Primary (1°) structure • Order of amino acids in chain • amino acid sequence determined by gene (DNA) • slight change in amino acid sequence can affect protein’s structure & it’s function • even just one amino acid change can make all the difference! lysozyme: enzyme in tears & mucus that kills bacteria
Secondary (2°) structure • “Local folding” • folding along short sections of polypeptide • interaction between adjacent amino acids • H bonds between R groups • -helix • -pleated sheet
“Let’s go to the video tape!” (play movie here) Secondary (2°) structure
Tertiary (3°) structure • “Whole molecule folding” • determined by interactions between R groups • hydrophobic interactions • effect of water in cell • anchored by disulfide bridges(H & ionic bonds)
Quaternary (4°) structure • More than one polypeptide chainjoined together • only then is it a functional protein • hydrophobic interactions collagen = skin & tendons hemoglobin
Chaperonin proteins • Guide protein folding • provide shelter for folding polypeptides • keep the new protein segregated from cytoplasmic influences
Denature a protein • 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 In Biology,size doesn’t matter, SHAPE matters!
multiplepolypeptides hydrophobic interactions aa sequence peptide bonds determinedby DNA R groups H bonds Protein structure (review) R groups hydrophobic interactions, disulfide bridges 3° 1° 2° 4°
Let’s build some Proteins!