Protein Function Chapter 5 2 5 3 Biochem 4511 Figures Essentials of Biochemistry 3rd Ed OSU Custom Edition Principles of Biochemistry 5th Ed Moran et al Lehninger Principles of Biochemistry 5th Ed Nelson Cox Fundamentals of Biochemistry 2nd Ed Voet Voet Pratt Structural proteins Keratins Hair nails claws rigid tissues Sulfur content defines rigidity Intermediate filaments solely structural in role Tissue characteristics based on molecular properties coiled coils aligning to make fibers Collagens Connective tissue skin Ropelike fibers chemical crosslinking provide support in tissues of animals Most abundant animal protein Tissue characteristics based on molecular properties collagen triple helix amino acid modifications and unusual covalent bonds Keratin Keratins Coiled coils Hydrophobic a d positions X Y here are buried twist of helices due to 3 6 residues per turn Keratins Coiled coils Coiled coils align to form oligomers End domains help align fibers Keratins stretch pulling on an a helix unwinds it Once fully extended domains or peptide bonds snap with additional force Fibers can peel apart split ends Collagen Triple Helix Gly Pro Hydroxyproline sequences form left handed coils The coils coil around each other as a right handed triple helix Resistant to compression due to counterwinding like a rope also high tensile strength Crosslinks increase with age vary with collagen type Triple helices assemble to form collagen fibrils Alignment of fibers generates well known banding pattern EM of collagen below Collagen and Scurvy Ascorbic acid is required by the enzymes that convert proline to hydroxyproline and lysine to hydroxylysine In the absence of vitamin C collagen can not be processed correctly and scurvy occurs This can be reversed by eating vitamin C No need for molecular details Know concepts Collagen and Scurvy Conversion of Pro to Hyp leads to oxidation of an enzyme bound Fe2 to Fe3 Vitamin C is required for a second reaction which reduces the Fe3 back to Fe2 reactivating the enzyme Just for fun No need for molecular details Fun Facts Collagen and Scurvy A 1998 study at Arizona State University found that 10 of students suffered from serious vitamin C deficiencies Eat fresh fruits and vegetables fruits such as citrus strawberries leafy greens peppers tomatoes and broccoli little trees As always too much of anything can be bad for you Vitamin C does have an upper limit for safe consumption and too much can lead to kidney stones and other issues Microtubules and microfilaments Tubulin microtubules Actin microfilaments Monomeric G and filamentous F actin exist in dynamic equilibrium Build up and break down fibers for example cell motility Also connection for motor proteins as below ADP Pi actin ATP actin ADP actin ADP actin ADP Pi actin ATP actin ATP dependent head neck movement here kinesin Myosin rigid neck muscle fibers contract Kinesin microtubule or myosin V actin flexible neck motor protein Inner life of the cell Harvard youtube Book Problems Problems 49 51 52 63 65 collagen in foods and or cooking 60 is an excellent question but advanced Look at it if you have time or love collagen Actin microfilaments
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