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Proteins PowerPoint Presentation

Proteins

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Proteins

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  1. Proteins Pages 42 to 46

  2. Proteins • Chemical composition • Carbon • Hydrogen • Oxygen • Nitrogen • Sulfur (sometimes) • Monomer/Building Block • Amino Acids (20 different amino acids)

  3. Table 5-1

  4. Fig. 5-UN1 carbon Carboxyl group Amino group

  5. Fig. 5-18 Peptide bond (a) A peptide bond is the bond joining adjacent amino acids. Side chains Peptide bond Backbone Amino end (N-terminus) Carboxyl end (C-terminus) (b)

  6. 4 Levels of organization of a protein • Primary - peptide bond joining adjacent amino acids • Secondary - Hydrogen bonding between nonadjacent amino acids that creates an alpha helix or pleated sheets • Tertiary - bond formation between R-groups; clustering of hydrophobic (nonpolar) or hydrophilic (polar) R-groups, disulfide bridges, ionic bonding, grouping based on pH, etc… that results in 3-dimensional folding • Quaternary – joining of more than one polypeptide (not all proteins have this level)

  7. Fig. 5-21 Tertiary Structure Primary Structure Secondary Structure Quaternary Structure  pleated sheet +H3N Amino end Examples of amino acid subunits  helix

  8. Fig. 5-21b 1 5 +H3N Amino end 10 Amino acid subunits 15 20 25 75 80 90 85 95 105 100 110 115 120 125 Carboxyl end

  9. Fig. 5-21c Secondary Structure  pleated sheet Examples of amino acid subunits  helix

  10. Fig. 5-21f Hydrophobic interactions and van der Waals interactions Polypeptide backbone Hydrogen bond Disulfide bridge Ionic bond

  11. Fig. 5-21g Polypeptide chain  Chains Iron Heme  Chains Hemoglobin Collagen

  12. Importance of structure • A slight change in primary structure can affect a protein’s structure and ability to function • Sickle-cell disease, an inherited blood disorder, results from a single amino acid substitution in the protein hemoglobin

  13. Fig. 5-22 Normal hemoglobin Sickle-cell hemoglobin Primary structure His Val Leu Glu Glu His Thr Val Primary structure Thr Pro Val Leu Pro Glu 1 2 3 4 5 6 7 1 2 3 4 5 6 7 Exposed hydrophobic region Secondary and tertiary structures Secondary and tertiary structures  subunit  subunit     Sickle-cell hemoglobin Quaternary structure Normal hemoglobin (top view) Quaternary structure     Function Molecules interact with one another and crystallize into a fiber; capacity to carry oxygen is greatly reduced. Function Molecules do not associate with one another; each carries oxygen. 10 µm 10 µm Red blood cell shape Normal red blood cells are full of individual hemoglobin moledules, each carrying oxygen. Red blood cell shape Fibers of abnormal hemoglobin deform red blood cell into sickle shape.