BIOCHEMISTRY - L. Stryer - 1984

VOLUME 2

PART II GENERATION AND STORAGE OF METABOLIC ENERGY

CHAPTER 19. PHOTOSYNTHESIS

QUESTIONS AND PROBLEMS

1. Calculate ∆E⁰ and ∆G⁰' for the reduction of NADP⁺ by soluble ferredoxin.

2. Sedoheptulose-1,7-bisphosphate is an intermediate in The Calvin Cycle but not in the Pentose Phosphate Pathway. What is the enzymatic basis for this difference?

3. Suppose that Photosynthesis is proceeding actively in an illuminated suspension of Chlorella when the light is suddenly turned off. How will the levels of 3-phosphoglycerate and ribulose 1,5-bisphosphate change over the next minute?

4. Suppose that photosynthesis was proceeding actively in an illuminated suspension of Chlorella in the presence of 1% CO₂, when the CO₂ concentration was suddenly dropped to 0.003%. What effect would this decrease have on the levels of 3-phosphoglycerate and ribulose 1,5-bisphosphate in the following minute?

5. In addition to chlorophyll a, the photosynthetic apparatus of blue-green Algae contains large amounts of phycoerythrin and phycocyanin. The absorption maximum of phycoerythrin lies between 480 and 600 nm, and that of phycocyanin is around 620 nm. Propose a role for these accessory Photosynthetic Pigments.

6. Van Niel's equation for photosynthesis in higher plants is as follows:

6СO₂ + 12Н₂O → С₆Н₁₂О₆ + 6Н₂O + 6O₂.

a) H₂O appears on both sides of this equation. Is this of purely formal significance, or does it reflect an important aspect of the photosynthetic mechanism?

b) The following equation is conventionally used to describe Respiration:

С₆Н₁₂O₆ + 6O₂ → 6СO₂ + 6Н₂O.

Does van Niel's equation (written in reverse) provide a more complete Description of the mechanism of respiration? In other words, does the combustion of glucose require the utilization of six molecules of H₂O?

7. METABOLISM/14.html">Chloroplasts illuminated in the absence of ADP and P_i synthesize ATP during a subsequent dark period upon The addition of ADP and P_i. The amount of ATP synthesized in the dark is markedly increased if pyridine is added prior to illumination. Why?

8. 3-(3,4-Dichlorophenyl)-1,1-dimethylurea (DCMU), a herbicide, uncouples Photophosphorylation and O₂ evolution in the absence of an artificial electron acceptor. However, it does not block the Hill reaction. Propose a site of inhibitory action for this herbicide.