Question

In the Dark Reaction or Calvin Cycle for every 6 molecules of _______________________ , only _______ can be used to generate simple sugars, fats, and AA’s.

A. CO2; 2

B. 3-phosphoglycerate; 2

C. 3-phosphoglycerate; 1

D. glyceraldehyde 3-phosphate; 1

E. glyceraldehyde 3-phosphat

Answer 1

in the Dark reaction or Calvin cycle for every 6 molecules of glyceraldehyde 3- phosphate, only 1 can be used to generate simple sugars, fats and amino acids. Whereas, rest 5 are used for regeneration of RubisCO

Hence, option D is correct.

Operation of Calvin cycle in stroma of chloroplast is the main process of CO2 fixation. This fixation happens with the help of one 5 carbon containing enzyme RubisCO and it also uses products of light reaction like NADPH and ATP.

It happens in 3 key steps

Fixation- RubisCO binds with CO2 (3 molecule) and gives rise to 3 phosphoglycerate (6 molecule)

Reduction- 3 phosphoglycerate is reduced to glyceraldehyde 3 phosphate (6 molecule)- one molecule of glyceraldehyde 3 phosphate goes for sugar synthesis (,enzymes used are phosphoglycerate kinase,ATP and glyceraldehyde 3 phosphate dehydrogenase,NADPH)

Regeneration-5 molecules of G3P (3 Carbon) goes to regenerate 3 molecules of RubisCO (5 carbon)

Option A is incorrect as 3 molecules of CO2, produces 6 molecules of Glyceraldehyde 3 phosphate (G3P).

Option B and C are also incorrect, as 3 phosphoglycerate formation is first step of calvin cycle (Fixation) and 3 phosphoglycerate does not directly goes for sugar synthesis or RubisCO regeneration. It first undergoes phosphorylation (by using ATP and enzyme phosphoglycerate kinase) followed by reduction (by using NADPH and enzyme G3P dehydrogenase).

Option E is also incorrect as it is misspelled version of glyceraldehyde 3 phosphate without any indication of number of moleules used.