AP Biology Proteins

AP Biology Proteins  Most structurally & functionally diverse group of biomolecules  Function:  involved in almost everything  enzymes  structure (keratin, collagen)  carriers & transport (membrane channels)  receptors & binding (defense)  contraction (actin & myosin)  signaling (hormones)  storage (bean seed proteins)

AP Biology Proteins  Structure:  monomer = amino acids  20 different amino acids  polymer = polypeptide  protein can be 1 or more polypeptide chains folded & bonded together  large & complex molecules  complex 3-D shape

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 H | —C— | C—OH || O R

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

AP Biology

AP Biology Sulfur containing amino acids  Disulfide bridges  cysteines form cross links

AP Biology Building proteins  Peptide bonds: dehydration synthesis  linking NH 2 of 1 amino acid to COOH of another  C–N bond peptide bond

AP Biology Building proteins  Polypeptide chains  N-terminal = NH 2 end  C-terminal = COOH end  repeated sequence (N-C-C) is the polypeptide backbone  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 Protein structure & function  function depends on structure  all starts with the order of amino acids  what determines that order of amino acids? lysozyme: enzyme in tears & mucus that kills bacteria the 10 glycolytic enzymes used to breakdown glucose to make ATP

AP Biology Primary (1°) structure  Order of amino acids in chain  amino acid sequence determined by 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!

AP Biology Sickle cell anemia

AP Biology Secondary (2°) structure  “Local folding”  Folding along short sections of polypeptide  interaction between adjacent amino acids   -helix   -pleated sheet

AP Biology Secondary (2°) structure The Alpha Helix

Beta-Pleated Sheets 18

Representations of Protein Secondary Structure  lysozyme 19

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  Joins together more than 1 polypeptide chain  only then is it a functional protein 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 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

AP Biology Denature a protein  Disrupt 3° structure  pH  salt  temperature  unravel or denature protein  disrupts H bonds, ionic bonds & disulfide bridges  Some proteins can return to their functional shape after denaturation, many cannot

AP Biology Let’s build some Insulin!

AP Biology The insulin protein has two chains, with a total of 53 amino acids

The two chains are connected by disulfide bridges from cysteine molecules After you link together the primary sequence through dehydration synthesis, you can join the cysteines together!

Each side of the room will build an insulin molecule The abbreviations for the 20 amino acids are found in the table 

The amino acids are color coded by side group: non-polar, polar, acidic, and basic

Water molecules need to be removed by dehydration synthesis Join the amino acids together, then work on the cysteines (part of tertiary structure)

Ribosome Animations of Protein Synthesis Real Time Slo-mo Older – Gumby-Like Shows secondary structure of ribosome in action

Bonus Question (1 st group to answer gets candy) Some of the 20 amino acids are missing from insulin – name them all!