8a - Lecture 8: Secondary structure of proteins Friday,...

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Lecture 8: Secondary structure of proteins Friday, August 20, 2010
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The next level of protein structure, secondary structure (2°) involves how local sequences fold, in particular the backbone of the protein. A key feature of the peptide bond is that it has a resonance form that imparts partial double bond character to it Friday, August 20, 2010
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The consequence of this is that the peptide bond in proteins is PLANAR (think of ethylene from organic chemistry!). This can exist in two forms: trans and cis. Because of sterics, the trans peptide bond dominates. Friday, August 20, 2010
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Geometry of the CIS peptide bond Friday, August 20, 2010
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The result of this is that flexibility in the polypeptide chain is due to rotation around the two backbone bonds of the alpha-carbon Friday, August 20, 2010
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The geometry about these freely rotating bonds is referred to as the TORSION ANGLE (as opposed to the bond angle) Friday, August 20, 2010
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These two angles are called: alpha-carbon to nitrogen: PHI (Φ) alpha-carbon to carbonyl carbon: PSI (Ψ) Friday, August 20, 2010
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This note was uploaded on 11/12/2010 for the course CHEN 3320 at Colorado.

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8a - Lecture 8: Secondary structure of proteins Friday,...

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