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Proteins

Explore the fascinating world of proteins, molecules made of amino acids with various functions like enzymes, structure, and communication. Learn about protein synthesis, structure levels, and how amino acids bond to form polypeptides. Discover the crucial role of proteins in cell membranes, muscle building, and more.

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Proteins

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  1. Proteins

  2. 3.5 What Are Proteins? • Proteins are molecules composed of chains of amino acids • Proteins have a variety of functions • Enzymes are proteins that promote specific chemical reactions • Structural proteins (e.g., elastin) provide support

  3. Table 3-3

  4. Proteins • Most structurally & functionally diverse group • Function: involved in almost everything • enzymes (pepsin, DNA polymerase) • structure (keratin, collagen) • carriers & transport (hemoglobin, aquaporin) • cell communication • signals(insulin & other hormones) • receptors • defense (antibodies) • movement (actin & myosin) • storage (bean seed proteins)

  5. play a role in cell membrane function • receptor proteins: recognize and bind to substances wanting to enter membrane • transport proteins: help transport substances across cell membrane • build muscles

  6. Figure 3-17 Structural proteins Horn Hair Silk

  7. 3.5 What Are Proteins? • Proteins are molecules composed of chains of amino acids (continued) • Proteins are polymers of amino acids joined by peptide bonds • All amino acids have a similar structure • All contain amino and carboxyl groups • All have a variable “R” group • Some R groups are hydrophobic • Some are hydrophilic • Cysteine R groups can form disulfide bonds

  8. H O | —C— | H || C—OH —N— H Amino acids • Structure • central carbon • amino group • carboxyl group (acid) • R group (side chain) • variable group • different for each amino acid • confers unique chemical properties to each amino acid • like 20 different letters of an alphabet • can make many words (proteins) R Oh, I get it! amino = NH2 acid = COOH

  9. Figure 3-18 Amino acid structure variable group (R) amino group carboxylic acid group hydrogen

  10. 3 - Proteins (Honors) • contain C, H, O, and N (nitrogen) • amino acids (monomer) bonded together

  11. 3.5 What Are Proteins? • Amino acids are joined by dehydration synthesis • An amino group reacts with a carboxyl group, and water is lost • The covalent bond resulting after the water is lost is a peptide bond, and the resulting chain of two amino acids is called a peptide • Long chains of amino acids are known as polypeptides, or just proteins

  12. Figure 3-20 Protein synthesis dehydration synthesis amino acid amino acid water peptide amino group carboxylic acid group peptide bond amino group

  13. Building Proteins dehydration synthesis / condensation rxn: http://www.wisc-online.com/objects/index_tj.asp?objID=AP13304

  14. H2O 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 hemoglobin growthhormones Rubisco

  15. Figure 3-19 Amino acid diversity aspartic acid (asp) glutamic acid (glu) Hydrophilic functional groups phenylalanine (phe) leucine (leu) cysteine (cys) Hydrophobic functional groups Sulfur-containing functional group

  16. 3.5 What Are Proteins? • A protein can have as many as four levels of structure • Primary structure is the sequence of amino acids linked together in a protein • Secondary structure is a helix, or a pleated sheet • Tertiary structure refers to complex foldings of the protein chain held together by disulfide bridges, hydrophobic/hydrophilic interactions, and other bonds • Quaternary structure occurs where multiple protein chains are linked together

  17. Animation: Protein Structure

  18. Figure 3-21 The four levels of protein structure Primary structure: The sequence of amino acids linked by peptide bonds Secondary structure: Usually maintained by hydrogen bonds, which shape this helix leu val heme group lys lys gly his hydrogen bond ala lys val Quaternary structure: Individual polypeptides are linked to one another by hydrogen bonds or disulfide bridges Tertiary structure: Folding of the helix results from hydrogen bonds with surrounding water molecules and disulfide bridges between cysteine amino acids lys helix pro

  19. Figure 3-22 The pleated sheet and the structure of silk protein hydrogen bond stack of pleated sheets strand of silk disordered segment Pleated sheet Structure of silk

  20. H2O peptidebond Building proteins • Peptide bonds • covalent bond between NH2 (amine) of one amino acid & COOH (carboxyl) of another • C–N bond dehydration synthesis

  21. Building proteins • Polypeptide chains have direction • N-terminus = NH2 end • C-terminus = COOH end • repeated sequence (N-C-C) is the polypeptide backbone • can only grow in one direction

  22. hemoglobin collagen Protein structure & function • Function depends on structure • 3-D structure • twisted, folded, coiled into unique shape pepsin

  23. 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 & its function • even just one amino acid change can make all the difference! lysozyme: enzyme in tears & mucus that kills bacteria

  24. Secondary (2°) structure • “Local folding” • folding along short sections of polypeptide • interactions between adjacent amino acids • H bonds • weak bonds between R groups • forms sections of 3-D structure • -helix • -pleated sheet

  25. Secondary (2°) structure

  26. Sulfur containing amino acids • Formdisulfide bridges • covalent cross links betweens sulfhydryls • stabilizes 3-D structure H-S – S-H You wonderedwhy permssmell like rotten eggs?

  27. Tertiary (3°) structure • “Whole molecule folding” • interactions between distant amino acids • hydrophobic interactions • cytoplasm is water-based • nonpolar amino acids cluster away from water • H bonds & ionic bonds • disulfide bridges • covalent bonds between sulfurs in sulfhydryls (S–H) • anchors 3-D shape

  28. Quaternary (4°) structure • More than one polypeptide chain bonded together • only then does polypeptide become functional protein • hydrophobic interactions hemoglobin collagen = skin & tendons

  29. Protein structure (review) R groups hydrophobic interactions disulfide bridges (H & ionic bonds) 3° multiple polypeptides hydrophobic interactions 1° amino acid sequence peptide bonds 4° 2° determinedby DNA R groups H bonds

  30. 3.5 What Are Proteins? • The functions of proteins are related to their three-dimensional structures • Precise positioning of amino acid R groups leads to bonds that determine secondary and tertiary structure • Disruption of secondary and tertiary bonds leads to denatured proteins and loss of function

  31. In Biology,size doesn’t matter, SHAPE matters! Protein denaturation • Unfolding a protein • conditions that disrupt H bonds, ionic bonds, disulfide bridges • temperature • pH • salinity • alter 2° & 3° structure • alter 3-D shape • destroys functionality • some proteins can return to their functional shape after denaturation, many cannot

  32. Denatured protein

  33. Just 1out of 146amino acids! Sickle cell anemia I’mhydrophilic! But I’mhydrophobic!

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