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 ( α 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 & hydrophilic?

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 between sulfur atoms in cysteine 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 backbone  interaction between adjacent amino acids  H bonds between R groups   -helix   -pleated sheet

AP Biology Secondary (2°) structure “Let’s go to the video tape!” (play movie here)

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)

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 “

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

AP Biology Chaperonin proteins  Guide protein folding  provide shelter for folding polypeptides  keep the new protein segregated from cytoplasmic influences

AP Biology Protein models  Protein structure visualized by  X-ray crystallography  extrapolating from amino acid sequence  computer modelling lysozyme