Molecular Biology Of The Cell 6th Edition by Bruce Alberts, Alexander Johnson, Julian Lewis, David Morgan, Martin Raff, Keith Roberts, Peter Walter

Exercise 11

0 ATP synthase is the world's smallest rotary motor. Passage of ions through the membrane-embedded portion of ATP synthase (the component) causes rota- tion of the single, central, axle-like ubunit inside the head group. The tripartite head is composed of the three dimers, the subunit of which is responsible for syn- thesis of ATP. The rotation of the subunit induces con- formational changes in the dimers that allow ADP and Pi to be converted into ATP. A variety of indirect evidence had suggested rotary catalysis by ATP synthase, but seeing is believing. To demonstrate rotary motion, a modified form of the complex was used. The subunits were modified so they could be firmly anchored to a solid support and the subunit was modified (on the end that normally inserts into the component in the inner membrane) so that a fluorescently tagged, readily visible filament of actin could be attached (Figure Q14-2A). This arrangement allows rotations of the subunit to be visualized as revolutions of the long actin filament. In these experiments, ATP syn- thase was studied in the reverse of its normal mechanism by allowing it to hydrolyze ATP. At low ATP concentrations, the actin filament was observed to revolve in steps of 1 and then pause for variable lengths of time, as shown in Figure Q14-2B.
A. Calculate the energy of a mole of photons ( photons/mole) at 400 nm (violet light), at 680 nm (red light), and at 800 nm (near-infrared light).
B. Bright sunlight strikes Earth at the rate of about 1.3 kJ/sec per square meter. Assuming for the sake of calcula- tion that sunlight consists of monochromatic light of wave- length 680 nm, how many seconds would it take for a mole of photons to strike a square meter?
C. Assuming that it takes eight photons to fix one molecule of as carbohydrate under optimal condi- tions (8-10 photons is the currently accepted value), cal- culate how long it would take a tomato plant with a leaf area of 1 square meter to make a mole of glucose from Assume that photons strike the leaf at the rate calculated above and, furthermore, that all the photons are absorbed and used to fix
D. If it takes 468 kJ/mole to fix a mole of into carbohydrate, what is the efficiency of conversion of light energy into chemical energy after photon capture? Assume again that eight photons of red light (680 nm) are required to fix one molecule of