ch369_sum10_class5_notes

ch369_sum10_class5_notes - Myoglobin & Hemoglobin....

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(examples of protein structure and function) Animals need a constant supply of oxygen. Myoglobin and hemoglobin are oxygen binding proteins. Myoglobin is abundant inside muscle cells. Hemoglobin is found in red blood cells, and transports O 2 .
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prosthetic group ” called a “ heme ”. The heme group is bound in a hydrophobic pocket in the protein core. The heme group can reversibly bind oxygen O 2 . Myoglobin ribbon diagram (wikipedia). heme Myoglobin was the first protein to have its structure determined John Kendrew received Nobel prize in 1962.
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The heme group binds in a hydrophobic pocket in the protein core. Not covalently bound. Bound by hydrophobic interactions.
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The iron (Fe 2+ ) gives the heme a red color. Fe 2+ can bind 6 ligands (“octohedral coordination”). 4 ligands contributed by the porphoryrin ring, one ligand from a histidine, leaving one space available for binding O 2 . O 2 heme
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Fraction of myoglobin molecules with O 2 bound. This binding curve has a “hyperbolic” shape. O 2 pressure (torr) The binding curve says: When there is a lot of O 2 present, a large fraction of myoglobin molecules have O 2 bound. Myoglobin binding O 2
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Since myoglobin was the first protein to have its structure determined, it is one of the most well studied proteins in biology. Surprisingly, mice that have been genetically engineered to lack myoglobin appear to be pretty healthy and are fertile. Reference: Mammen et al., Heart and Circ. Physiol., 285, H2132 (2003). Perhaps myoglobin has other functions for O 2 storage in muscle tissue, or binding oxygen free radicals (O 2 - )? Although it is clear that myoglobin binds O 2 , its full physiological function may not be fully understood.
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Hemoglobin picks up O 2 in the lungs, and releases it at tissue that need it. Hemoglobin returns to the lungs with carbon dioxide for release. You can’t live without hemoglobin. Hemoglobin - another oxygen binding protein with a heme group.
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Hemoglobin is a “tetramer”, with 4 peptide chains, and 4 heme groups. “Quaternary structure” describes how the 4 peptide chains are arranged. Hemoglobin tetramer, with 2 of the (red) heme groups visible. Hemoglobin tetramer contains 2 alpha chains and 2 beta chains. Alpha and beta chains are similar but not identical in a.a. sequence.
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The hemoglobin subunits are similar in structure to myoglobin. Apparently, myoglobin and hemoglobin have a common ancestor protein.
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If one heme group has a bound O 2 , it increases the ability of the other heme groups to bind O 2 (this is called “ cooperative binding ”). The quaternary structure of hemoglobin allows for a type of structural communication between the 4 peptide chains called allostery ”.
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structures of hemoglobin.
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ch369_sum10_class5_notes - Myoglobin & Hemoglobin....

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