Question

In the process of carbon fixation, RuBP attaches a CO2 to produce a six-carbon molecule, which is then split to produce two molecules of 3-phosphoglycerate. After phosphorylation and reduction produces glyceraldehyde 3-phosphate (G3P), what more needs to happen to complete the Calvin cycle?
A. addition of a pair of electons from NADPH
B. regeneration of ATP from ADP
C. regeneration of RuBP
D. regeneration of NADP+
E. inactivation of RuBP carboxlyase enzyme

Answer 1

Answer:

C. regeneration of RuBP

Explanation:

To complete the calvin cycle, RuBP regeneration must occur. At this stage, five of the six 3-phosphoglyceraldehyde molecules are used to regenerate three RuBP molecules.

Since each round of the Calvin cycle one carbon dioxide molecule is reduced and one RuBP is regenerated, three rounds of the cycle, with the introduction of three carbon atoms, are required to produce a glyceraldehyde 3-phosphate molecule, phosphorylated form of C3H6O3.

Answer 2

Answer:

C

Explanation:

The Calvin cycle occurs in three major phases:

1) Carbon fixation; which involves the reaction of CO2 with a phosphorylated Co2 acceptor called Ribulosebiphosphate(RuBp) as catalysed by Rubisco enzyme. Due to the instability of the formed six-carbon compound, it breaks into two molecules of 3-phosphoglycerate (PGA)

2) Reduction; The PGA is phosphorylated by ATP to form 1,3-biphosphoglycerate, which is then reduced by NADPH to form glyceraldehyde-3-phosphate (G3P).

3) Regeneration; The final step, which is very important for the continuity of Calvin cycle is the regeneration of the CO2 acceptor (RUBP). The molecules of G3P are rearranged into molecules of Ribulosephosphate(RuP) by series of complex reactions, which is then phosphorylated by ATP to form RUBP, ready to accept CO2 for the cycle to continue