8) (6 pts) Herbicide X blocks electron flow from Photosystem II to the Cytochrom

Question

8) (6 pts) Herbicide X blocks electron flow from Photosystem II to the Cytochrome bf complex during photosynthesis. A) Predict the effect that Herbicide X will have on O2 production. B) Will NADPH be produced when Herbicide X is present? C) When plants are exposed to Herbicide X, ATP synthesis is less than what is seen if it is not present, but some ATP synthesis does still occur. Explain these observations. 9) (10 pts) During an experiment in your lab, a green plant is exposed to "C labeled carbon dioxide (CO2). Shortly afterwards you isolate the following compounds from the plan phosphoglycerate, glucose, erythrose-4-phosphate, ribose-5-phosphate and sedoheptulose 7- phosphate. Using "C NMR you then examine these isolated compounds. A) Draw a structure for each substance you isolated. B) Circle the carbon(s) that will be isotopically labeled in your experiment and explain fully why the carbons you circled will be isotopically labeled. ) (8 pts) Using liver extracts to study the oxidation of fatty acids, you make the following observations: 1) When myristate (14:0) is provided as the substrate, it is completely oxidized to Co 2) When tridecanoic acid (13:0) is added as the substrate, incomplete oxidation occurs unless CO, is bubbled through the reaction mixture. 3) The addition of avidin, which binds biotin strongly, prevents complete oxidation of tridecanoic acid under any circumstances, although it has no effect on myristate oxidation. Explain each observation given what you know about fatty acid catabolism

Explanation / Answer

8. A) O2 production will decrease because electrons and protons produced by photolysis of water is not removed by cytochrome bc complex. Thus it will block the linear photophosphorylation (Z-scheme) and hence photosystem II will not be contributing, in turn, oxygen formation will stop.

B) NADPH production will stop since linear photophosphorylation is broken. Only cyclic photophosphorylation will occur which will alone can not produce NADPH.

C) The herbicide X has no effect on photosystem I (P700), so cyclic photophosphorylation will continue to produce ATP.

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