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Carbon Fixation Cylce - HSN forum

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Carbon Fixation Cylce


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#1 spoony2oo8

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Posted 21 May 2008 - 03:17 PM

Does It Require The Carbon Fixation Cycle To Go Twice For A Molcule Of Glucose To Be Made? As The (6x3C) Triose Phosphate Molecules Give Off One And The Rest Is Used To Regeneratr RuBP. Is That Correct?
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#2 anna123

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Posted 21 May 2008 - 05:54 PM

from sqa:

Coverage of the Calvin cycle should be done in such a way that the number of carbons is accounted for
throughout the cycle with indications of the position of entry of (a) carbon dioxide which is accepted by
the 5-carbon compound ribulose 1,5-bisphosphate (RuBP) and (b) hydrogen which is accepted by the 3-carbon compound glycerate 3-phosphate (GP). It should be stressed that these reactions, which require ATP and hydrogen provided by the light dependent stage, essentially involve the reduction of carbon dioxide to form carbohydrate.
Candidates are not required to name intermediate chemical compounds except GP (PGA) and RuBP (RuDP).
Mention should be made of the fact that the major biological molecules in plants (eg proteins, fats, carbohydrates, nucleic acids) are derived from the photosynthetic process.

1. A five-carbon sugar molecule called ribulose bisphosphate, or RuBP, is the acceptor that binds CO2 dissolved in the stroma. This process, called CO2 fixation, is catalyzed by the enzyme RuBP carboxylase, forming an unstable six-carbon molecule. This molecule quickly breaks down to give two molecules of the three-carbon 3-phosphoglycerate (3PG), also called phosphoglyceric acid (PGA).

2. The two 3PG molecules are converted into glyceraldehyde 3-phosphate (G3P, a.k.a. phosphoglyceraldehyde, PGAL) molecules, a three-carbon sugar phosphate, by adding a high-energy phosphate group from ATP, then breaking the phosphate bond and adding hydrogen from NADH + H+.

3. Three turns of the cycle, using three molecules of CO2, produces six molecules of G3P. However, only one of the six molecules exits the cycle as an output, while the remaining five enter a complex process that regenerates more RuBP to continue the cycle. Two molecules of G3P, produced by a total of six turns of the cycle, combine to form one molecule of glucose.

#3 spoony2oo8

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Posted 22 May 2008 - 08:41 AM

So It Is Basically Takes 6CO2 To Make One Glucose?
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#4 anna123

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Posted 22 May 2008 - 11:48 AM

to be honest i'm not really sure but i found some stuff hope it helps!! sorry

Three turns of the cycle, using three molecules of CO2, produces six molecules of G3P. However, only one of the six molecules exits the cycle as an output, while the remaining five enter a complex process that regenerates more RuBP to continue the cycle. Two molecules of G3P, produced by a total of six turns of the cycle, combine to form one molecule of glucose.

http://library.thinkquest.org/C004535/calvin_cycle.html





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