TAILIEUCHUNG - Biochemistry, 4th Edition P52

Biochemistry, 4th Edition P52. Continuing Garrett and Grisham's innovative conceptual and organizing framework, "Essential Questions," BIOCHEMISTRY guides students through course concepts in a way that reveals the beauty and usefulness of biochemistry in the everyday world. Streamlined for increased clarity and readability, this edition also includes new photos and illustrations that show the subject matter consistently throughout the text. New end-of-chapter problems, MCAT practice questions, and the unparalleled text/media integration with the power of CengageNOW round out this exceptional package, giving you the tools you need to both master course concepts and develop critical problem-solving skills you can draw upon. | Special Focus 473 transmitted to the subunit interfaces where they trigger conformational readjustments that lead to the rupture of interchain salt links. The Oxy and Deoxy Forms of Hemoglobin Represent Two Different Conformational States Hemoglobin resists oxygenation see Figure because the deoxy form is stabilized by specific hydrogen bonds and salt bridges ion-pair bonds Figure . All of these interactions are broken in oxyhemoglobin as the molecule stabilizes into a new conformation. The shift in helix F upon oxygenation leads to rupture of the Tyr 8145 Val 898 hydrogen bond. In deoxyhemoglobin with these interactions intact the C-termini of the four subunits are restrained and this conformational state is termed T the tense or taut form. In oxyhemoglobin these C-termini have almost complete freedom of rotation and the molecule is now in its R or relaxed form. The Allosteric Behavior of Hemoglobin Has Both Symmetry MWC Model and Sequential KNF Model Components Oxygen is accessible only to the heme groups of the -chains when hemoglobin is in the T conformational state. Max Perutz has pointed out that the heme environment of -chains in the T state is virtually inaccessible because of steric hindrance by amino acid residues in the E helix. This hindrance disappears when the hemoglobin molecule undergoes transition to the R conformational state. Binding of O2 to the -chains is thus dependent on a T-to-R conformational shift and this shift is triggered by the subtle changes that occur when O2 binds to the -chain heme groups. Together these observations lead to a model that is partially MWC and partially KNF O2 binding to one -subunit and then the other leads to sequential changes in conformation followed by a switch in quaternary structure at the Hb 2O2 state from T to R. Thus the real behavior of this protein is an amalgam of the two prominent theoretical models for allosteric behavior. H Promotes the Dissociation of Oxygen from Hemoglobin Protons carbon

• Sinh học
• Nền tảng của hóa sinh học
• trao đổi chất protein
• RNA trao đổi chất
• nguyên tắc của hóa sinh
• Axit amin
• công nghệ DNA