Question

With reference to three Calvin cycles, which of the given options is correct for the following questions?
I. How many gross PGAL molecules are produced?
II. Total, how many ATP molecules are required for synthesis of PGAL molecules?
III. Total, how many NADPH${}_2$ molecules are required for the synthesis of obtained PGAL molecules?

• A. I= 3 PGAL, II = 3 ATP, III = 3 NADPH${}_2$
• B. I= 6 PGAL, II = 6 ATP, III = 6 NADPH${}_2$
• C. I= 18 PGAL, II = 18 ATP, III = 18 NADPH${}_2$
• D. I= 9 PGAL, II = 9 ATP, III = 9 NADPH${}_2$

Answer 1

The correct option is B I= 6 PGAL, II = 6 ATP, III = 6 NADPH${}_2$

In one Calvin cycle, 1 $C{O}_2$ (1 carbon) combines with 1 molecule of Ribulose bisphosphate (5 carbon) to form 2 molecules of 3-phosphoglycerates (3 carbon each). The 2 molecules of 3-phosphoglycerates (PGA) in a couple of steps are converted to 2 molecules of Glyceraldehyde-3- phosphate (PGAL - 3 carbon). In this entire process of formation 2 molecules of PGAL, a total of 2 ATP and 2 NADPH are utilized. So, for 3 cycles, net PGAL will be 6, ATP and NADPH consumption will allso be 6. Thus, the correct option is B.