Questions of Week_16 Feb

There are a few issues to note, some of which I have already highlighted in some classes so here goes if you miss it in class.

1)In Calvin Cycle, the reduction reaction has NADPH becoming NADP+ and the release of Pi.
Qn: Where did the Pi come from? Where did the H+ go?

Ans:
a)Pi comes from the ATP earlier on and which was incorporated into GP before its release later on
b)H+ was incorporated into the organic molecule 1,3 bisphosphoglycerate, a molecule after GP, to become G3P. See diagrams below:





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2) Rubisco the term is given with reference to its role as a carboxylase. When we talk about it being a oxygenase, how do we refer to it?

We still call it Rubisco but pointing out that it serves as a oxygenase (when required)


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3)Why did the 1st ETC in light-dependent reaction pump H+ but not the 2nd one?

Hummpf.. it was noted in lecture that the proteins that make up the two chains are different and thus yes, there is a H+ pump in the 1st ETC but not in the 2nd one. If you want to know more, you have to find out how the proteins are arranged with respect to one another and even to the thylakoid membrane.

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4) Calvin Cycle: How many turns to make one glucose molecule or any hexose sugar?

It is 6 turns. Each CO2 can only be fixed on one RuBP at any one time. Each turn of the cycle will generate 2 G3P, one with an atmospheric C fixed into it but not the other. You already know that for every 12 G3P generated (6 turns), the system will somehow be able to regulate and send only 2 G3P out of the cycle to form glucose and 10 G3P remain in the cycle for regeneration of RuBP.
Qn: So does that mean that each cycle will generate 1/3 of a G3P to be transported out?
To reconcile that:
By now, you might realise that there is many RuBP to serve as CO2 acceptors. So at any one time, you can have 6 RuBP accepting 6 CO2 such that you will get a pool of 12 G3P at some point and of which 10 will return back to cycle(s) and 2 will be siphoned off. =)

--- easier to imagine?

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5) Tutorial Qn (roughly lah): where does photophosphorylation take place?
- thylakoid membrane/grana

Can we talk about formation of ATP at the stroma side of the membrane?

Yes. Based on the definition, it is one up to you. It is perfectly fine to have that, even better.

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That's all folks!!
Good luck for test =)