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I have a biology question.

A photo of brady23 brady23
I don't know the answer to this question in my textbook. Can anyone help me?

The question is: What would be an ideal enzyme in photosynthesis to regulate by feedback inhibition. How could this enzyme be regulated?

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4 replies
 
A photo of Mas40 Mas40
hey

that is indeed a very hard question...

here is some text that i found, hopefully it is helpful

http://jxb.oxfordjournals.org/content/54/382/539.full

Good Luck!
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A photo of brady23 brady23

@Mas40 wrote
hey

that is indeed a very hard question...

here is some text that i found, hopefully it is helpful

http://jxb.oxfordjournals.org/content/54/382/539.full

Good Luck!



Thank you! I don't know the answer, and my school's biology department is pretty tough, so I'm trying to get as much practice as I can.

My textbook asks the same question for glycolysis, but I think I know that one is the enzyme phosphofructokinase.
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A photo of newageanubis newageanubis
For glycolysis, phosphofructokinase is inhibited by citrate/citric acid from the Kreb cycle.

As for photosynthesis, I think ribulose-1,5-bisphosphate carboxylase-oxygenase is a fairly good candidate. If the enzyme were downregulated by feedback inhibition, the plant would be able to reduce the incidence of photorespiration. Any Calvin cycle intermediate could inhibit the enzyme. I think 1,3-bisphosphoglycerate is good candidate for that because it's far enough from the carboxylation reaction, but present in a relatively large concentration.

Another candidate I can think of is ferredoxin-NADP+ reductase. Once enough carbohydrates are synthesized, non-cyclic photophosphorylation isn't really required until carbohydrates are needed again. Any of the Calvin cycle intermediates could inhibit this enzyme; I would say 1,3-bisphosphoglycerate, again.

Hope I helped somehow. Good luck! :)
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A photo of brady23 brady23

@newageanubis wrote
For glycolysis, phosphofructokinase is inhibited by citrate/citric acid from the Kreb cycle.

As for photosynthesis, I think ribulose-1,5-bisphosphate carboxylase-oxygenase is a fairly good candidate. If the enzyme were downregulated by feedback inhibition, the plant would be able to reduce the incidence of photorespiration. Any Calvin cycle intermediate could inhibit the enzyme. I think 1,3-bisphosphoglycerate is good candidate for that because it's far enough from the carboxylation reaction, but present in a relatively large concentration.

Another candidate I can think of is ferredoxin-NADP+ reductase. Once enough carbohydrates are synthesized, non-cyclic photophosphorylation isn't really required until carbohydrates are needed again. Any of the Calvin cycle intermediates could inhibit this enzyme; I would say 1,3-bisphosphoglycerate, again.

Hope I helped somehow. Good luck! :)




Thank you, that question did come up on the test, and I put NADP+ reductase for the reason you said, and I got 3.5 / 4 on that question! :D

I only lost 0.5 because she was looking for Protein Z because she said that the enzyme you want to regulate should be earliest in photosynthesis to minimize energy waste, but we had freedom with which enzyme we wanted to choose.
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