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Chapter 5 Amino Acids, Peptides, and Proteins

Chapter 5 Amino Acids, Peptides, and Proteins. Lecture 1 of 2 Learn Pages 115 – 129 Learn to draw 20 standard amino acids (page 119). Red blood cells contain the oxygen transporting protein hemoglobin. Proteins Abundant biomolecule Occur in all cells and all parts of cells

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Chapter 5 Amino Acids, Peptides, and Proteins

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  1. Chapter 5 Amino Acids, Peptides, and Proteins Lecture 1 of 2 Learn Pages 115 – 129 Learn to draw 20 standard amino acids (page 119) Red blood cells contain the oxygen transporting protein hemoglobin

  2. Proteins • Abundant biomolecule • Occur in all cells and all parts of cells • Occur in great variety (small to really large) • Polymers of amino acids • Joined by a specific type of covalent bond • All proteins are built from the same set of 20 amino acids • Covalently linked in characteristic linear sequence • Exhibit diversity in biological functions

  3. General Structure of an Amino Acid Side chain is different in each amino acid All amino acids have this general structure except proline which is cyclic

  4. Amino acid R • carbon is bound to four different groups • carbon atom is a chiral center

  5. Stereoisomerism in a-amino acids The object and its mirror image are not superimposable

  6. Project out of the plane of the paper behind it

  7. Assumed to project out of the plane of the paper behind it

  8. Steric relationship of the stereoisomers of alanine to the absolute configuration of L- and D- glyceraldehyde L-amino acids have a amino group on left a R group below a C • l and d designations were used historically for levo and dextro rototary • Not all L-amino acids are levorotatory

  9. The amino acid residues in proteins are exclusively L stereoisomers • Formation of stable repeating substructures in proteins require the amino acids to be only one stereo isomer • Cells can specifically synthesize L isomers amino acid because the active site of the enzymes are asymmetric causing the reactions catalyzed to be stereospecific

  10. Need to know the single & 3 letter abbreviation

  11. R Group S containing

  12. R groups are nonpolar (hydrophobic) Can form H bonds

  13. S containing Cyclic

  14. Reversible formation of a disulfide bond by the oxidation of two molecules of cysteine Disulfide bonds stabilize the structure of many proteins

  15. Nonstandard amino acids No need to learn to draw Some of these are found in proteins

  16. Amino acids can act as acids and bases Forms of amino acids Does not occur in significant amounts in aqueous solution Predominates at neutral pH

  17. Amino acids have characteristic titration curves At this pH predominant species is species 2 (dipolar ion) 1 2 3 At midpoint in the first stage of titration [species 1] = [species 2] At low pH predominant species is species 1 pKa of Carboxyl group = 2.34 pKa of amino group = 9.6

  18. Formation of a peptide bond

  19. The Pentapeptide Ser-Gly-Tyr-Ala-Leu or Serylglycyltyrosylalanylleucine N or C or

  20. NutraSweet

  21. Levels of structure in proteins Linking of aa Stable arrangement of aa give rise to structural patterns 3-dimensional folding of polypeptides Arrangement in space of 2 or more polypeptide subunits

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