It consists of four different polypeptide chains known as I
CF0 conducts protonsĪcross the thylakoid membrane, whereas CF1 catalyzes the formation of ATP from ADP and Pi.ĬF0 is embedded in the thylakoid membrane. Synthase closely resembles the F1-F0 complex of mitochondria (Section 18.4). The proton-motive force generated by the light reactions is converted into ATP by the ATP synthase ofĬhloroplasts, also called the CF 1 -CF 0 complex (C stands for chloroplast and F for factor). The ATP Synthase of Chloroplasts Closely Resembles Those of Mitochondriaand Membrane corresponds to a proton-motive force of 0 V or a G of -4 kcal mol-1 (-20 kJ mol-1). A pH gradient of 3 units across the thylakoid Maintained and no membrane potential is generated. Induced transfer of H+ into the thylakoid space is accompanied by the transfer of either Cl- in the sameĭirection or Mg2+ (1 Mg2+ per 2 H+) in the opposite direction. Reason for this difference is that the thylakoid membrane is quitepermeable to Cl- and Mg2+. PH gradient, whereas, in mitochondria, the contribution from the membrane potential is larger. In chloroplasts, nearly all of p arises from the Inherent in the proton gradient, called the proton-motive force ( p), is described as the sum of twoĬomponents: a charge gradient and a chemical gradient. Light-induced transmembrane proton gradient is about 3 pH units. The thylakoid space becomes markedly acidic, with the pH approaching 4. Such a gradient can be maintainedīecause the thylakoid membrane is essentially Lumen or taken up from the stroma, generating a proton gradient. At various stages in this process, protons are released into the thylakoid We have seen how light induces electron transfer through photosystems II and The principles by which ATP synthesis takes place in chloroplasts are nearly identical with those for Unequivocally support the hypothesis put forth by Peter Mitchell that ATP synthesis is driven by proton. This incisive experiment was one of the first to A burst of ATP synthesis then accompanied the disappearanceof the pH gradientĪcross the thylakoid membrane (Figure 19). The pH of the stroma suddenly increased to 8, whereas the pH of the thylakoid To create this transient pH gradient, he soakedĬhloroplasts in a pH 4 buffer for several hours and then rapidly mixed them with a pH 8 bufferĬontaining ADP and Pi.
Gradient is imposed across the thylakoid membrane. In 1966, André Jagendorf showed that chloroplasts synthesize ATP in the dark when an artificial pH These conclusions are corroborated by the finding that only the membrane potential induces a rotary torque that drives the counter-rotation of the a and c subunits in the F(o) motor of Propionigenium modestum ATP synthase.A Proton Gradient Across the Thylakoid Membrane Drives ATP Synthesis Hence, the membrane potential and proton gradient are not equivalent under normal operating conditions far from equilibrium. Recent experiments demonstrate, however, that the chloroplast ATP synthase, like those of mitochondria and bacteria, requires a membrane potential for ATP synthesis. The two components were considered to be not only thermodynamically but also kinetically equivalent, since the chloroplast ATP synthase appeared to operate on delta pH only. The proton-motive force consists of two components, the transmembrane proton concentration gradient (delta pH) and the membrane potential.
#DESCRIBE HOW THE PROTON GRADIENT DRIVES ATP SYNTHESIS FREE#
ATP, the universal carrier of cell energy, is manufactured from ADP and phosphate by the enzyme ATP synthase using the free energy of an electrochemical gradient of protons (or Na(+)).
0 kommentar(er)
