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Chem4711%28Noteset3%29-1

Chem4711%28Noteset3%29-1 - Protein structure fibrous...

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Protein structure - fibrous proteins Fibrous proteins vs. globular proteins fibrous = structural with only a single secondary structure repeated many times = insoluble in water (high proportion of hydrophobic residues) (globular = enzymes and regulatory proteins)
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Protein structure - keratin (hair, wool, nails, claws, quills, hooves, outer layer of skin)
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Protein structure - keratin Rich in Val, Leu, Ile, Met, Phe (pack against each other) Stabilize proto-fibril bundles with S-S covalent cross-links (up to 18% of total residues can be Cys in rhino-horn)
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Protein structure - keratin Hair-chemistry: stretch alpha-helices to sheets in the presence of a reducing agent, curl, wash out reducing agent and let hair cool…..
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Protein structure - collagen p116ff Connective tissue: tendons, cartilage, organic matrix of bone, eye cornea Unique secondary structure: - left-handed helix - 3 residues per turn Unique quaternary structure: - coiled coil - right-handed twist Enriched for Gly, Ala, Pro, Hyp Typical sequence = Gly-X-Y (where X=Pro and Y=Hyp)
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Protein structure - collagen
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Protein structure - collagen
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Protein structure - collagen and vitamin C Vitamin C is essential for biosynthesis of Hyp. Symptoms of scurvy = degeneration of connective tissue Proline hydroxylase N p e p t i d e p e p t i d e O O H O O C C O O H + O 2 F e + + N p e p t i d e p e p t i d e O O H C O O H C O O H + + C O 2 (Vitamin C acts as a reductant to keep enzyme active)
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Protein structure - collagen cross-linking (not Cys-Cys) (too much cross-linking in old age => rigid and brittle)
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Collagen - cross-linking QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. Lysyl oxidase: -specific for collagen -requires copper and vitamin B6 -inhibited by nitriles: β -aminopropionitrile found in seeds of sweet peas causes lathyrism = deformation of the spine, demineralization of the bones, disolcation of joints. -lack of copper in a pig diet = same symptoms as lathyrism (age) p 136 - 159
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Collagen - cross-linking p 136 - 159 QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. (collagenase is an enzyme that digests collagen) Age: -more cross-linking with more age -stiffer skin, blood vessels, other tissues - -meat from older animals is tougher than young meat
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Protein structure - experimental techniques X-ray crystallography - crystallize protein at high concentrations - take a “picture” using X-ray diffraction - solve “phase” problem - build model into electron density - quality of structure depends on resolution Crystals 40-60% H 2 O - similar to cells!
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Protein structure - X-ray crystallography
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Protein structure - X-ray crystallography
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Protein structure - X-ray crystallography
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Protein structure - X-ray crystallography
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Protein structure - X-ray crystallography
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