The Calvin cycle, also known as the C3 cycle, consists of three main phases: carboxylation, reduction, and regeneration of RuBP. During carboxylation, CO2 is captured by RuBP to form an unstable compound that splits into 3-phosphoglyceric acid (3PGA). The cycle ultimately produces hexose sugars and regenerates RuBP, allowing the process to continue.

1. Calvin Cycle
Department Of Botany
Prepared by
Dr. P. B. Cholke
(Assistant Professor in Botany)
Pune District Education Association’s
Anantrao Pawar College ,Pirangut,
Tal-Mulshi, Dist-Pune- 412115

2. • worked out by professor Melvin Calvin.
• It is also known as C3 cycle because the 1st
stable products is of 3 carbon compound i.e.
phosphoglyceric acid (PGA).

3. • C3 cycle completes in 3 steps.
• A. Carboxylation phase.
• B. Reduction phase.
• C. Regeneration of RUBP

4. • A. Carboxylation phase :
• i. RUBP (Rubulose-1, 5-Bi phosphate)
acceptor CO2 from atmosphere to form
unstable 6 carbon compound with the help of
enzyme RUBP carboxylase.
• ii. The 6 carbon compound quickly splits into
two molecules of 3C compounds called 3-
phosphoglyceric acid (3PGA)

6. • B. Reduction phase :
• i. 3PGA is phosphorylated to 1,3-diPGA with
the help of ATP molecule.
• ii. 1,3-DiPGA is reduced to 3-
phosphoglyceraldehyde (3PGAL) by using H2
from NADPH2.

7. • C. Regeneration of RUBP :
• i. Two molecules of 3PGAL forms hexose sugar
which is store in the form of starch.
• ii. The remaining 3PGA molecules are converted
into RUMP (5C) to continue the cycle by forming
some sugar intermediate compounds such as
Erythrose (4C), Sedoheptulose (7C).
• iii. RUMP (5C) is converted to RUBP (5C) with the
help of ATP molecule.
•