Review - Exam 2 Review Myoglobin verse Hemoglobin(Chapter 5...

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2/22/11 Exam 2 Review Myoglobin verse Hemoglobin ( Chapter 5 ) Both globular proteins Myoglobin Small protein Heme group binds O2 Located in muscles and tissue (facilitates oxygen diffusion through muscle cells or binds other small molecules such as nitric oxide) Lacks beta structure entirely and all but 32 of 153 AA residues are part of 8 alpha helices Hemoglobin Heme groups bind O2 cooperatively (reversely) Located in blood Heterotetramer (tetrameric whose 4 subunits resemble myoglobin, 2 alpha, 2 beta chains) Each subunit called a Globin , which looks a lot like myoglobin The 4 subunits undergo conformational changes when they bind O2 The alpha and beta chains and myoglobin have similar tertiary structures Exists as deoxyhemoglobin and oxyhemoglobin (two different quaternary structures) -Heme is a type of Prosthetic Group - organic compound that allows a protein to carry out some function that the polypeptide alone cannot perform-in this case binding oxygen. Hemoglobin Oxygen-Binding Curve Sigmoidal curve (S-shaped) Overall Oxygen affinity lower than myoglobin (O2 released from hemoglobin in the lungs is released to myoglobin in the muscles) At low O2 concentrations, hemoglobin appears to be reluctant to bind the first O2, but as pO2 increases, O2 binding increases sharply, until hemoglobin is almost fully saturated. 4 heme groups work together in cooperative binding behavior p50 is 26 torr Myoglobin Oxygen-Binding Curve Hyperbolic curve As the O2 concentration increases, more and more O2 molecules bind to the heme groups of myoglobin molecules until as very high O2 concentrations, virtually all the myoglobin molecules have bound O2. Myoglobin is then said to be saturated with oxygen
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Concentration of O2 at which Y is half maximal is equivalent to K p50 is 2.8 torr Deoxyhemoglobin (hemoglobin w/o any bound O2) T for “tense” Unfavorable for O2 binding Oxyhemoglobin (hemoglobin with bound O2) R for “relaxed” Favorable for O2 binding -Hemoglobin is an allosteric protein - binding of one small molecule (ligand) to one site alters the ligand-binding affinity of the other sites. -In Hemoglobin, the ligands are all oxygen molecules, and O2 binding to one part of the protein increases the O2 affinity of the rest of the protein. The Bohr effect About pH Increasing pH of a solution of hemoglobin (decreasing H+) favors O2 binding (curve moves to the left) Decreasing the pH (increasing H+) favors O2 dissociation (curve moves to the right) The reduction of hemoglobin’s oxygen-binding affinity when the pH decreases is known as the Bohr Effect . BPG
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Review - Exam 2 Review Myoglobin verse Hemoglobin(Chapter 5...

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