BiochemF2019.Lecture4.pptx.pdf - Hydrogen Bonds Polypeptide Secondary Structure the Alpha Helix Hydrogen Bonds Polypeptide Secondary Structure the Alpha

BiochemF2019.Lecture4.pptx.pdf - Hydrogen Bonds Polypeptide...

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Unformatted text preview: Hydrogen Bonds & Polypeptide Secondary Structure: the Alpha Helix Hydrogen Bonds & Polypeptide Secondary Structure: the Alpha Helix Basis for Alpha Helix Structure: H-­bonds Between Carbonyl Oxygen of ith Amino Acid and Amino Hydrogen in i+4th Amino Acid Structure of Ferritin, an Iron Storage Protein A Fully Extended Polypeptide Segment: the β-­strand Hydrogen Bonds & Polypeptide Secondary Structure: β-­sheets β-­Sheet Formed by Anti-­parallel β-­Strands: Each Amino Acid Forms Two H-­bonds with One Other Amino Acid β-­Sheet Formed by Parallel β-­Strands: Each Amino Acid Forms One H-­bond with Each of Two Other Amino Acids Structure of a “Mixed” β-­Sheet with Parallel and Anti-­parallel β-­Strands R-­Groups in β-­Sheets Are Oriented Above & Below Plane of Sheet Representation of a Fatty Acid Binding Protein Rich in β-­Sheets Polypeptide Loops Are Stabilized by Hydrogen Bonds Coiled-­coil Proteins Composed of Superhelices of Entwined α-­Helices Held Together by van der Waals Forces, Ionic Bonds, Disulfide Bonds Collagen: Composed of Three Polypeptide Strands Held Together in a Superhelix by Hydrogen Bonds Primary Structure of a Portion of a Collagen Polypeptide: Note Regular Spacing of Glycine and Large # of Prolines A Collagen Strand: a Helix Formed as a Result of Steric Repulsion of the Pyrrolidine Rings of Proline Tertiary Structure: Protein Folding is Driven by Hydrophobicity in an Aqueous Environment: the Example of Myoglobin External View of Myoglobin Internal/Cross Sectional View of Myoglobin Blue = Charged AA’s Yellow = Hydrophobic AAs Tertiary Structure: Porins are Membrane Proteins with a β-Barrel Structure, Hydrophobic Exterior & Hydrophilic Interior “Motifs”: Common Structural Elements of Proteins. Example: the Helix-­turn-­helix Motif of DNA Binding Proteins Three DNA-­binding Proteins Containing Helix-­turn-­helix Motifs Proteins May Be Composed of Separate Domains Connected by Flexible Segments Example: Extracellular Domains of the CD4 Cell Surface Protein of Immune Cells Quaternary Structure: Multiple Polypeptides Associate to Form a Functional Protein Ex: the Bacteriophage Cro Protein – a Homodimer Quaternary Structure: Human Hemoglobin – a Heterotetramer Composed of 2 α-­globin Subunits and 2 β-­globin Subunits Primary Structure and Disulfide Bonds of Bovine Ribonuclease β-­Mercaptoethanol: a Reducing Agent that Breaks Disulfide Bonds Reduction & Denaturation of Ribonuclease Anfinsen’s Experiment: Spontaneous Refolding of RNase Provided Evidence that “Sequence Specifies Conformation” The Importance of Protein Structure: Alternative Forms of the Prion Protein PrPC PrPSc Model for the Conversion and Transmission of the Prion Protein ...
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