Question

Which one is the first stable product of C3 cycle soon after the uptake of CO2?

• A. 3-PGA
• B. DHAP
• C. 3-PGAl
• D. Phosphoribulose

Hint:

Think about what RuBP splits into right after RuBisCO acts on CO2.

Answer 1

The Correct Option is A

Step 1: The Calvin cycle begins when RuBisCO catalyses carboxylation of ribulose 1,5-bisphosphate (RuBP) using CO2.

The resulting 6 carbon compound is too unstable to persist and breaks apart into two 3 carbon acid molecules right away.

This 3 carbon acid, 3-phosphoglycerate, is therefore the earliest stable product of the cycle, before ATP and NADPH later reduce it to G3P (3-PGAl) and DHAP. Answer: 3-PGA.