Question

What does the following diagram not show​

Answer 1

Answer:

Calvin cycle is a complete biosynthetic pathway discovered by Melvin Calvin. It is also known as C

3

pathway because the first stable product identified was 3-phophoglyceric acid (PGA). Calvin cycle occurs in all photosynthetic plants whether they have C

3

or C

4

pathway.

Calvin cycle can be described under three stages:

Carboxylation: It is the fixation of CO

2

into a stable organic intermediate. In this, CO

2

is utilised for the carboxylation of RuBP. This reaction is catalysed by the enzyme RuBisCO and it results in the formation of two molecules

of 3-PGA (3-phosphoglyceric acid.

Reduction: These reactions lead to the formation of glucose. The steps involve utilisation of two molecules of ATP for phosphorylation and two of NADPH for reduction, per molecule of CO

2

fixed. The fixation of six molecules of CO

2

and six turns of the cycle are required for the removal of one molecule of glucose from the pathway.

Regeneration: For the cycle to continue uninterrupted, regeneration of the CO

2

acceptor molecule is crucial. This step requires one ATP for phosphorylation to form RuBP. To make one molecule of glucose, six turns of the cycle are required. 18 ATP and 12 NADPH molecules are used to make a molecule of glucose.

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