Proteins

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Proteins
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• Proteins

Multipurposemolecules
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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)

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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
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Amino acids

• Structure
• central carbon
• amino group
• carboxyl group (acid)
• R group (side chain)
• variable group
• confers unique chemical properties of the amino
  acid

R
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Nonpolar amino acids
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Polar amino acids
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Sulfur containing amino acids

• Form disulfide bridges
• cross links betweens sulfurs in amino acids

H-S S-H
You wonderedwhy permssmelled like rotten eggs?
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Building proteins

• Peptide bonds
• linking NH2 of one amino acid to COOH of another
• CN bond

dehydration synthesis
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Protein structure function

• Function depends on structure
• 3-D structure
• twisted, folded, coiled into unique shape

pepsin
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Primary (1) structure

• Order of amino acids in chain
• amino acid sequence determined by gene (DNA)
• slight change in amino acid sequence can affect
  proteins structure its function
• even just one amino acid change can make all the
  difference!

lysozyme enzyme in tears mucus that kills
bacteria
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Sickle cell anemia
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Secondary (2) structure

• Local folding
• folding along short sections of polypeptide
• interaction between adjacent amino acids
• H bonds between R groups
• ?-helix
• ?-pleated sheet

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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)

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Quaternary (4) structure

• More than one polypeptide chain joined together
• only then is it a functional protein
• hydrophobic interactions

collagen skin tendons
hemoglobin
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Protein structure (review)
R groups hydrophobic interactions, disulfide
bridges
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1
2
4
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• Lets build some
• Proteins!

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Protein models

• Protein structure visualized by
• X-ray crystallography
• extrapolating from amino acid sequence
• computer modelling

lysozyme
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Any Questions??