TAILIEUCHUNG - Báo cáo sinh học: "What is cooperativity"

Tuyển tập các báo cáo nghiên cứu về sinh học được đăng trên tạp chí sinh học Journal of Biology đề tài: What is cooperativity? | Journal of Biology BloMed Central Question Answer Q A Cooperativity James E Ferrell Jr What is cooperativity Cooperativity is a type of behavior where a number of seemingly independent components of a system act collectively in unison or near-unison. Think of a school of fish a flock of birds or a pack of lemmings. Cooperativity implies some sort of communication among the system s seemingly independent components. In biochemistry the term cooperativity is almost always used in one particular context binding-dissociation reactions at equilibrium. The classic example is the binding of oxygen to hemoglobin Figure 1 . But cooperativity is also important in cell-cell signaling transcriptional regulation and more complex processes governing the behavior of cells. Figure I The oxygen-transporting protein hemoglobin a tetrameric protein consisting of four globin subunits with four oxygen-binding hemes. Reproduced with permission from Michael W King. What is the importance of cooperativity That depends on the system but let s take hemoglobin. Hemoglobin s mission is to pick up a large amount of oxygen in the lungs where the oxygen concentration or partial pressure is about 100 torr and then drop off a good Address Department of Chemical and Systems Biology Stanford University School of Medicine Stanford CA 94305-5174 USA. Email fraction of it in the peripheral tissues where the oxygen concentration is about 20 torr. Cooperativity helps make this transport efficient. To see why first suppose that hemoglobin were a monomeric oxygen binding protein Figure 2 . Figure 2 Monomeric oxygen-transporting protein. If the binding and dissociation reactions are described by simple mass action kinetics then hemoglobin s oxygen saturation at equilibrium would be given by the Langmuir equation x y - K x where y is the oxygen saturation x is the partial pressure of oxygen and K is the dissociation constant. Because this equation is identical in form to the .

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