Figure Q14–2 Experimental set-up for observing rotation of the  γ subunit of atp synthase (problem 14–10). (a) the immobilized α3β3γ complex. the β subunits are anchored to a solid support and a fluorescent actin filament is attached to the γ subunit. (B) Stepwise revolution of the actin filament. the indicated trace is a typical example from one experiment. the inset shows the positions in the revolution at which the actin filament pauses. (B, from r. yasuda et al., Cell 93:1117–1124, 1998. With permission from Elsevier.) are plants at converting light energy into chemical energy? The answers to these questions provide an important backdrop to the subject of photosynthesis.
Each quantum or photon of light has energy hv, where h is Planck’s constant (6.6 × 10–37 kJ sec/photon) and v is the frequency in sec–1. The frequency of light is equal to c/λ, where c is the speed of light (3.0 × 1017 nm/ sec) and λ is the wavelength in nm. Thus, the energy (E) of a photon is
A. Calculate the energy of a mole of photons (6 × 1023 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 calculation that sunlight consists of monochromatic light of wavelength 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 CO2 as carbohydrate under optimal conditions (8–10 photons is the currently accepted value), calculate how long it would take a tomato plant with a leaf area of 1 square meter to make a mole of glucose from CO2. Assume that photons strike the leaf at the rate calculated above and, furthermore, that all the photons are absorbed and used to fix CO2.
D. If it takes 468 kJ/mole to fix a mole of CO2 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 CO2.
14–12 In chloroplasts, protons are pumped out of the stroma across the thylakoid membrane, whereas in mitochondria, they are pumped out of the matrix across the crista membrane. Explain how this arrangement allows chloroplasts to generate a larger proton gradient across the thylakoid membrane than mitochondria can generate across the inner membrane.
14–13 Examine the variegated leaf shown in Figure Q14–3. Yellow patches surrounded by green are common, but there are no green patches surrounded by yellow. Propose an explanation for this phenomenon.
Figure Q14–3 a variegated leaf of Aucuba japonica with green and yellow patches (problem 14–13).
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The Mitochondrion
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