CHE 472 Problem Set #5- Photosynthesis
1) The equation for photosynthetic reduction of CO2 to carbohydrate can also be written as:
CO2 + 2H2O  ---> (CH2O) + O2 + H2O.
a) Are the oxygen atoms of O2 derived  from  the oxygen atoms of H2O, CO2 or both?
b) How could this be answered experimentally?
2) a) Photosynthetic bacteria produce use H2S and produce elemental sufur,  while others use ethanol and produce acetaldehyde. Write net reactions for photosynthesis (corresponding to the equation shown in #1) for these bacteria.
b) Why is no oxygen produced in these bacteria?
c) Write a general equation for the photosynthetic fixation of CO2 to carbohydrate using H2A as the hydrogen donor.

3) The herbicide 3-(3,4-dichlorophenyl)-1,1-demethyl urea (DCMU) blocks photosynthetic electron transport from PSII to the cytochrome bf complex.

a) when DCMU is added to isolated chloroplasts, will both O2 evolution and photophosphorylation cease?
b) If an external electron acceptor that reoxidizes P680* is added, how will this effect O2 production and photophosphorylaton?


4) a) The luminal pH of chloroplasts suspended in a solutions of pH 4.0 reaches pH 4.0 within a few minutes. Explain why there is a burst of ATP synthesis when the pH of the external solution is quickly raised to 8.0 and ADP and Pi are added.
b) If ample ADP and Pi are present why does ATP synthesis stop after a few seconds.

5) Cyclic electron transport may occur simultaneously with non cyclic electron transport under certain conditions. Are ATP, O2, and NADPH produced by cyclic electron transport?

6) Predict the effect of an uncoupler such as dintitrophenol on the production of: a) ATP or b) NADPH in a chloroplast.

7)  Describe the functional and structural similarities between the bacterial photosynthetic reaction center and PS II.

8)  In photosystem I, P700 in its groundstate has an Eo'=+0.4v. Excitation of P700 by a  photon of 700 nm light alters the Eo' to -0.6v.  What is the efficiency of energy capture in this light reaction of P700?

9) Assuming a concentration of ATP, ADP, and pi in chloroplasts are 3 mM, 0.1 mM, and 10 mM, respectively, what is the DG for ATP synthesis under these conditions? Photosynthetic electron transfer establishes a proton motive force driving phosphorylation. What redox potential difference is necessary to achieve ATP synthesis under the for-going conditions, assuming an electron pair is transferred per molecule of ATP generated?

10) In 1939 , Robert Hill discovered that chloroplasts evolve O2 when they are illuminated in  the presence of  an artificial electron acceptor such as ferricyanide [Fe3+(CN)6]3-. Ferricyanide is reduced to ferrocyanide [Fe2+(CN)6]4- in this process. No NADPH or reduced plastocyanin is produced.  Propose a mechanism for the Hill reaction.
 
 


Solutions to Problem Set 4:
 
Problem #1

Problem #2

Problem #3

Problem #4

Problem #5

Problem #6

Problem #7

Problem #8

Problem #9

Problem #10


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