Calvin Cycle or C3 Cycle Or Reductive Pentose Pathway

calvin cycle steps

This path of C-assimilation was given by Calvin, Benson and Bassham (1949). They got the Nobel Prize for this work in the year 1961. This is also known as C ₃ cycle because CO ₂ reduction is cyclic process and first stable product in this cycle is a 3-C compound (i.e.,3-Phosphoglyceric acid or 3-PGA).

Fig. Calvin cycle (C ₃ cycle)

In this cycle, CO ₂ acceptor molecule is RuBP or RuDP (i.e., Ribulose 1, 5-biphosphate or Ribulose 1, 5-diphosphate).

As Calvin cycle takes in only one carbon (as CO ₂ ) at a time, so it takes six turns of the cycle to produce a net gain of six carbons (i.e., hexose or glucose).

In this cycle, for formation of one mole of hexose sugar (Glucose), 18 ATP  and 12 NADPH ₂ are used.

The plants in which this pathway of CO ₂ reduction occurs, are called C ₃ plants.

Enzyme RUBISCO (RUBP carboxylase oxygenase) was also called earlier as carboxy dismutase.

RUBISCO is most abundant protein on earth and it is present on the outer surface of thylakoid membrane.