Calvin Cycle

The answer is: B. 20 PGAL.

Each cycle produces 2 PGAL (3C).
It takes 6 Cycle to make 1 glucose (6C) because 10 PGAL of the 12 PGAL produced is recycled back to 2 RBP (5C).

 

wait...glucose(6c) => 2 PGAL(3c) then it loses CO2 to become acetyl CoA. So basically, only 2c enters the calvin cycle, right?

what are the product after the 1 cycle? is it just 2 PGAL(6c)? could u explain this part to me? If I remember it right, acetyl CoA(2C) meets oexaloacetate (4C) and becomes (6C) and that's the beginning of the Calvin Cycle. During the Cycle, it loses 2CO2 to make 2NAD+ into 2NADH and 2H+, so we end up with 4C in the end of the cycle. Am I wrong?
Even in the Kaplan's blue book, it says " through a complicated series of reactiosn, 2 CO2 are released, and oxloacetate(4C) is regenerated for use in another turn of the cycle." you said that each cycle produces 6C(since u said 2 PGAL are produced) and I don't know why it's not 4C.

and when u said "in reality, it produces 6 PGAL and only releases 1PGAL in 3 cycle" I don't understand it again. If the answer for my 1st question is 2PGAL for each cycle and 3 cycle makes 6PGAL, why does only 1 PGAL is released and where did other 5PGAL go?

so could u explain these 2 things for me ?

 

bump~ anyone else know?

 

bump~

 

OMG!! I found out the truth of the Calvin Cycle!!!
I kept looking at the final product of the Calvin Cycle cuz the question asked what's left after the cycle.
so then 2C enters +4C waiting for 2C = 6C was MADE, and that's it!!!
I should stop there! and cuz even though that's the beginning of the cycle, that's the product!!!!! OMG!!!
and then! 2C out of 6C r used to make 2NADH +2H, and 4C that are left goes back to the cycle and wait for the 2C, just like the beginning of the Cycle!! OMG!!!
So basically onlly 2 C out of 6C are used and 4C out of 6C goes back to the CYCLE, OMG!!!
6C(glucose, or 2PGAL)is made per Cycle, OMG!! and I was keep thinking that "ok, 2 of them are used, so we only have 4left and that's the product" OMG!!! I am so happy!!! I didn't understand this for 1 week, and i studied this one question for 1 week..... I can't believe ppl study only a couple of weeks to study for DAT while i spent 1 entire week to study this 1 question...

 

I think you're mixing up the "Calvin Cycle" with the "Citric" or Kreb's Cycle. The Calvin cycle takes CO2 and adds it to RBP which is a five carbon sugar. This now 6 carbon sugar is unstable, so it splits into 2 PGA which is a 3 carbon molecule. 2 PGA are then converted to 2 PGAL by ATP and NADPH. For every 6 turns of the cycle, you get 2 free PGAL that combine and make glucose and 10 that you have to recycle back to RBP. PGAL can also be used on its own as an immediate food source if needed. If you keep track of all the carbons in 6 turns of the cycle, you get 12 PGAL = 36 carbons. 6 carbons go to glucose and 30 go to make 6 RBP(5 carbon sugar). Calvin cycle uses energy from the light cycle of photosynthesis to reduce CO2 into glucose. The Kreb's cycle is an energy producing step that harnesses the energy released when breaking down glucose. They are opposite reactions. This explanation is to the extent of my understanding. Sorry if I missed anything.

 

then ....i guess i have no idea what calvin cycle is... -_-;
when do i learn it? and do u know what page in kaplan book has this?

 

Look on page 117-118 in Kaplan DAT. Just remember that Calvin cycle deals with creating food (glucose) by harnessing the sun's energy, and Kreb's cycle deals with using glucose as an energy source. Calvin cycle is considered the dark reaction of photosynthesis, and comes after the light reaction, which takes sunlight and produces ATP and NADPH which is then used in the Calvin cycle to convert CO2 into glucose. Kreb's cycle is the 3rd step of 4 in aerobic respiration in which an organism uses the energy stored in glucose by breaking it down to create ATP which fuels the organism's activities. Glycolysis is the first step, then Pyruvate decarboxylation, then Kreb's or Citric acid cycle and lastly Electron transport chain. Look at pages 105-111. If you focus on the purpose of these cycle's first, then you can go into the detail and stay on track. Hope that helps. The fact that you spent a week on this problem shows you have persistence and that's a good thing. Good luck.