AP Biology Chemical Building Blocks 3.4 Proteins
AP Biology Proteins
AP Biology Proteins Multipurpose molecules
AP Biology 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)
AP Biology 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 Rubisco hemoglobin growth hormones
AP Biology Amino acids Structure: central carbon amino group carboxyl group (acid) R group (side chain) variable group confers unique chemical properties of the amino acid —N——N— H H C—OH || O R | —C— | H
AP Biology Nonpolar amino acids nonpolar & hydrophobic Why are these nonpolar & hydrophobic?
AP Biology Polar amino acids polar or charged & hydrophilic Why are these polar & hydrophillic?
AP Biology Ionizing in cellular waters H+ donors
AP Biology Ionizing in cellular waters H+ acceptors
AP Biology Sulfur containing amino acids Form disulfide bridges cross links betweens sulfurs in amino acids You wondered why perms smelled like rotten eggs? H-S – S-H
AP Biology Building proteins Peptide bonds linking NH 2 of one amino acid to COOH of another C–N bond peptide bond dehydration synthesis
AP Biology Building proteins Polypeptide chains N-terminus = NH 2 end C-terminus = COOH end repeated sequence (N-C-C) is the polypeptide backbone can only grow in one direction
AP Biology Protein structure & function hemoglobin Function depends on structure 3-D structure twisted, folded, coiled into unique shape collagen pepsin
AP Biology 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
AP Biology Sickle cell anemia
AP Biology Secondary (2°) structure “Local folding” folding along short sections of polypeptide interaction between adjacent amino acids H bonds between R groups -helix -pleated sheet
AP Biology Secondary (2°) structure
AP Biology 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) Van der Waals Force (velcro)
AP Biology Quaternary (4°) structure More than one polypeptide chain joined together only then is it a functional protein hydrophobic interactions hemoglobin collagen = skin & tendons “Let’s go to the video tape!” (play movie here)
AP Biology Protein structure (review) 1° 2° 3° 4° aa sequence peptide bonds R groups H bonds R groups hydrophobic interactions, disulfide bridges determined by DNA multiple polypeptides hydrophobic interactions
AP Biology 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!
AP Biology Let’s build some Proteins!
AP Biology Chaperonin proteins Guide protein folding provide shelter for folding polypeptides keep the new protein segregated from cytoplasmic influences
AP Biology Diseases as a result Cystic fibrosis; disables vital proteins from moving ions across membranes Alzheimers; protein clumping in brain cells Chaperone does fails to create correct folding.
AP Biology Protein models Protein structure visualized by X-ray crystallography extrapolating from amino acid sequence computer modelling lysozyme