Question

The carbon dioxide acceptor in Calvin cycle/$C_3$ plants is

• A. Phospho-enol pyruvate (PEP)
• B. Ribulose 1, 5-diphosphate (RuBP)
• C. Phosphoglyceric acid (PGA)
• D. Ribulose monophosphate (RMP)

Answer 1

The correct option is B Ribulose 1, 5-diphosphate (RuBP)

Calvin cycle occurs in all photosynthetic plants whether they have $C_3$ or $C_4$ pathway. The carbon dioxide acceptor in Calvin cycle is a five-carbon ketose sugar- Ribulose bisphosphate (RuBP). Its chemical name is Ribulose 1,5-diphosphate. The enzyme responsible for primary carboxylation in $C_3$ plants is RuBisCO. It stands for Ribulose Bisphosphate Carboxylase-Oxygenase. It is formed of a five-carbon ketose sugar- Ribulose bisphosphate (RuBP). It is characterized by the fact that its active site can bind to both $C{O}_2$ and $O_2$, hence the name. RuBisCO has a much greater affinity for $C{O}_2$ than for $O_2$ and the binding is competitive. It is the relative concentration of $O_2$ and $C{O}_2$ that determines which of the two will bind to the enzyme.