# PGAL and Calvin Cylce

#### Sublimation

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5+ Year Member
Ok let me get this straight cuz i got a Q like this from the kaplan practice test and it made no sense to me. Now it takes 6X turns of the calvin cycle to produce 1 glucose. Cliffs says that will produce 2PGAL. Thus every 6X turns of the calvin cylce we get 2 pgal and thus one glucose. Now kaplan says that 10 turns of the calvin cycle will produce 20 PGAL. now my Question. Is does it take 1 turn of the calvin cycle to produce 1 glucose or does it take 6? cuz if it takes 1 then i see how kaplan got their answer. however if its 6 i understand the logic behind cliffs. to me 6 sounds right. If someone can elaborate i would greatly appreciate it.

#### joonkimdds

##### Senior Member
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7+ Year Member
6turn makes one glucose is right.

each cycle only takes 1 CO2.
Glucose is 6C.
Thus 1c x 6 cycle = 6c.

Actually it's more complicated than what I wrote above

#### UCB05

Ok let me get this straight cuz i got a Q like this from the kaplan practice test and it made no sense to me. Now it takes 6X turns of the calvin cycle to produce 1 glucose. Cliffs says that will produce 2PGAL. Thus every 6X turns of the calvin cylce we get 2 pgal and thus one glucose. Now kaplan says that 10 turns of the calvin cycle will produce 20 PGAL. now my Question. Is does it take 1 turn of the calvin cycle to produce 1 glucose or does it take 6? cuz if it takes 1 then i see how kaplan got their answer. however if its 6 i understand the logic behind cliffs. to me 6 sounds right. If someone can elaborate i would greatly appreciate it.

I would bring that up with kaplan. Mechanistically, one single turn fixes one CO2 molecule, so 3 mechanistic turns nets one G3P. One single turn will not completely restore the ribulose, since you put one CO2 in and ideally get one PGAL out. So depending on the person/source, they may consider one "turn" of the Calvin Cycle as a reaction set that consumes one CO2, one that nets a PGAL (3 actual turns), or one that nets a Glucose (6 actual turns). Most textbooks consider one turn as the reaction set fixing 1 CO2 because they enter the reaction one at a time, and personally, I'd go with that definition.

#### Sublimation

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5+ Year Member
I would bring that up with kaplan. Mechanistically, one single turn fixes one CO2 molecule, so 3 mechanistic turns nets one G3P. One single turn will not completely restore the ribulose, since you put one CO2 in and ideally get one PGAL out. So depending on the person/source, they may consider one "turn" of the Calvin Cycle as a reaction set that consumes one CO2, one that nets a PGAL (3 actual turns), or one that nets a Glucose (6 actual turns). Most textbooks consider one turn as the reaction set fixing 1 CO2 because they enter the reaction one at a time, and personally, I'd go with that definition.

Thanks. I knew i had it right, but i was afraid i was missing something there. Thanks though

#### Thuy

I was confused too with Kaplan, but I just use this equation:

One turn of Calvin Cycle is 6 CO2 + 12 H2O --> C6H12O6 + 6 O2 + 6 H2O

SO 1 turn gives 1 Glucose (after 6 CO2 was used up in the photosynthetic reaction).

You should remember that 1 Glucose can be broken down into 2 PGAL
( remember GLYCOLYSIS).

As 1 Glucose gives 2 PGAL, ONE turn of Calvin cycle would give 2 PGAL.

I dunno know if it helps, but it works out for me that way. I guess Im more numerical than verbal learner

#### joonkimdds

##### Senior Member
10+ Year Member
7+ Year Member
I was confused too with Kaplan, but I just use this equation:

One turn of Calvin Cycle is 6 CO2 + 12 H2O --> C6H12O6 + 6 O2 + 6 H2O

SO 1 turn gives 1 Glucose (after 6 CO2 was used up in the photosynthetic reaction).

You should remember that 1 Glucose can be broken down into 2 PGAL
( remember GLYCOLYSIS).

As 1 Glucose gives 2 PGAL, ONE turn of Calvin cycle would give 2 PGAL.

I dunno know if it helps, but it works out for me that way. I guess Im more numerical than verbal learner

That's not correct. 1 turn only uses 1 CO2. 6 turn uses 6 CO2.

#### jjy850kme

Ok.
Here is what I know.

(3 x calvin cycle)
5 x 1,5 ribulosebisphospate + 3CO2 --> 6 x phosphoglycerate --> 6 x PGAL
1 of the PGAL goes out of the cycle and 5 x PGAL -->1,5 ribulosebisphosphate.

So two turns of Calvin cycle will generate 2 PGAL that goes out of the cycle and become glucose. (This is why 2 cycle is required to generate 1 glucose)

But in terms of producing PGAL(considering both PGAL that goes out of the cycle and the one that is used to generate ribulosebisphosphate) 3 x calvin cycle generates 6 x PGAL. (2 PGAL / 1 cycle)
Thus 10 turns of calvin cycle will produce 20 PGAL.

Hope this helps!

#### MTD52

##### Class of 2014
10+ Year Member
5+ Year Member
Ok let me get this straight cuz i got a Q like this from the kaplan practice test and it made no sense to me. Now it takes 6X turns of the calvin cycle to produce 1 glucose. Cliffs says that will produce 2PGAL. Thus every 6X turns of the calvin cylce we get 2 pgal and thus one glucose. Now kaplan says that 10 turns of the calvin cycle will produce 20 PGAL. now my Question. Is does it take 1 turn of the calvin cycle to produce 1 glucose or does it take 6? cuz if it takes 1 then i see how kaplan got their answer. however if its 6 i understand the logic behind cliffs. to me 6 sounds right. If someone can elaborate i would greatly appreciate it.

It doesn't say that in Cliffs. It says 6 turns is 12 PGAL.

Each turn uses 1CO2 (which has 1 Carbon) and glucose needs 6 carbons, so you need 6 turns to make glucose. Just think of it as each turn using 1 carbon. Each CO2 (+RBP) makes 2PGAL. Thus, 6 turns = 12GPAL. That's all you need to know for this question.

1) 6CO2 + 6RBP --> 12PGA
2) 12PGA + 12ATP + 12NADPH --> 12PGAL (or G3P, whichever you prefer)
3)**2 PGAL are used to make 1 molecule of glucose here**
3) 10PGAL + 6ATP --> 6RBP
4) New RBP is used to combine with 6CO2 and cycle repeats

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