What are the substrates and products of the Calvin CycleSolu

What are the substrates and products of the Calvin Cycle?

Solution

Answer:

Calvin cycle is the light independent reaction in photosynthesis and takes place in three steps:

(1) Fixation:

The 5-carbon Ribulose bisphosphate (RuBP) reacts with CO₂ catalysed by RuBP carboxylase in a process called fixation. For each molecule of CO₂ fixed, 2 molecules of 3-phosphoglyceric acid (3PGA) is produced.

(2) Reduction:

In this step, 3PGA is converted to glyceraldehyde-3-phosphate (G3P) mediated by ATP and NADPH. Since PGA accepts electrons, this is a reduction reaction.

(3) Regeneration:

After 3 rounds of the cycle, six G3P are formed but only one G3P is exported while the other five G3P are used in the regeneration of RuBP to fix more CO_2. Thus, two molecules of G3P from six cycles combine to form the 6-carbon glucose molecule.

Thus, the net equation of Calvin cycle is:

3CO₂ + 6NADPH + 5H2O + 9ATP glyceraldehyde-3-phosphate (G3P) + 2H⁺ + 6 NADP⁺ + 9 ADP + 8 Pi

Thus, the substrates are: RuBP, CO₂, ATP and NADPH

and the final products are: Glucose, ADP and NADP