Problem 1
Wavelengths The rate of photosynthesis in a green plant, measured by \(\mathrm{O}_{2}\) production, is higher when illuminated with light of wavelength \(680 \mathrm{~nm}\) than with light of wavelength 700 \(\mathrm{nm}\). However, illumination by a combination of light of 680 \(\mathrm{nm}\) and \(700 \mathrm{~nm}\) gives a higher rate of photosynthesis than light of either wavelength alone. Explain.
Problem 3
purple sulfur bacteria carry out photosynthesis in the presence of \(\mathrm{H}_{2} \mathrm{O}\) and \({ }^{14} \mathrm{CO}_{2}\), but only if \(\mathrm{H}_{2} \mathrm{~S}\) is added and \(\mathrm{O}_{2}\) is absent. During photosynthesis, measured by formation of \(\left[{ }^{14} \mathrm{C}\right]\) carbohydrate, the bacteria convert \(\mathrm{H}_{2} \mathrm{~S}\) to elemental sulfur but do not produce \(\mathrm{O}_{2}\). What is the role of the conversion of \(\mathrm{H}_{2} \mathrm{~S}\) to sulfur? Why doesn't photosynthesis produce \(\mathrm{O}_{2}\) in these bacteria?
Problem 4
how an inhibitor of electron passage through pheophytin would affect electron transfer through (a) photosystem II and (b) photosystem I. Explain your reasoning.
Problem 7
Effect of Venturicidin on Oxygen Evolution Venturicidin is a powerful inhibitor of the chloroplast ATP synthase, interacting with \(\mathrm{CF}_{\mathrm{o}}\) and blocking proton passage through the \(\mathrm{CF}_{0} \mathrm{CF}_{1}\) complex. How would venturicidin affect oxygen evolution in a suspension of well-illuminated chloroplasts? Would your answer change if the experiment were done in the presence of an uncoupling reagent such as 2,4 dinitrophenol (DNP)? Explain.
Problem 10
Energetics of Phototransduction During photosynthesis, pigment molecules in chloroplasts must absorb eight photons (four by each photosystem) for every \(\mathrm{O}_{2}\) molecule they produce, according to the equation $$ 2 \mathrm{H}_{2} \mathrm{O}+2 \mathrm{NADP}^{+}+8 \text { photons } \rightarrow 2 \mathrm{NADPH}+2 \mathrm{H}^{+}+\mathrm{O}_{2} $$ The \(\Delta G^{\prime \circ}\) for the light-independent production of \(\mathrm{O}_{2}\) is 400 \(\mathrm{kJ} / \mathrm{mol}\). Assuming that these photons have a wavelength of \(700 \mathrm{~nm}\) (red) and that the light absorption and use of light energy are \(100 \%\) efficient, calculate the free- energy change for the process.
Problem 11
Electron Transfer to a Hill Reagent Isolated spinach chloroplasts evolve \(\mathrm{O}_{2}\) when illuminated in the presence of potassium ferricyanide (a Hill reagent), according to the equation $$ 2 \mathrm{H}_{2} \mathrm{O}+4 \mathrm{Fe}^{3+} \rightarrow \mathrm{O}_{2}+4 \mathrm{H}^{+}+4 \mathrm{Fe}^{2+} $$ where \(\mathrm{Fe}^{3+}\) represents ferricyanide and \(\mathrm{Fe}^{2+}\) represents ferrocyanide. Does this process produce NADPH? Explain.
Problem 12
How Often Does a Chlorophyll Molecule Absorb a Photon? The amount of chlorophyll \(a\left(M_{\mathrm{r}} 892\right)\) in a spinach leaf is about \(20 \mu \mathrm{g} / \mathrm{cm}^{2}\) of leaf surface. In noonday sunlight (average energy reaching the leaf is \(5.4 \mathrm{~J} / \mathrm{cm}^{2} \cdot \mathrm{min}\) ), the leaf absorbs about \(50 \%\) of the radiation. How often does a single chlorophyll molecule absorb a photon? Given that the average lifetime of an excited chlorophyll molecule in vivo is 1 ns, what fraction of the chlorophyll molecules are excited at any one time?
Problem 17
Regulation of the Calvin Cycle Iodoacetate reacts irreversibly with the free - SH groups of Cys residues in proteins. Predict which Calvin cycle enzyme(s) would be inhibited by iodoacetate, and explain why.
Problem 19
Compare the oxidative photosynthetic carbon cycle, also called photorespiration, with the mitochondrial respiration that drives ATP synthesis. Why are both processes referred to as respiration? Where in the cell do they occur, and under what circumstances? What is the path of electron flow in each?
Problem 21
Identifying CAM Plants Given some \({ }^{14} \mathrm{CO}_{2}\) and all the tools typically present in a biochemistry research lab, how would you design a simple experiment to determine whether a plant is a typical \(\mathrm{C}_{4}\) plant or a \(\mathrm{CAM}\) plant?
