Question

3 PGA is first stable product of

• A. Carbon oxidation cycle
• B. Carbon reduction cycle
• C. Reductive amination
• D. Malic acid synthesis

Answer 1

The correct option is B Carbon reduction cycle

In $C{O}_2$ Fixation, the $C{O}_2$ that diffuses into the stroma of the chloroplast in mesophyll cells is added (covalently bonded) to the five-carbon acceptor ribulose-1,5-bisphosphate (RuBP, $C_5{H}_{12}{O}_{11}{P}_2$), also called ribulose-1,5-diphosphate (RuDP), yielding a six-carbon intermediate product. This intermediate is hydrated and then cleaved, producing two molecules of three-carbon 3-phosphoglycerate or phosphoglyceric acid (3-PGA or simply PGA, $C_3{H}_5{O}_{6}P$) as the first stable product. The reaction is catalyzed by the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCo). This first stable product (3-PGA), being a three-carbon compound, is the reason why this mechanism of photosynthesis is called C3 Cycle.

So, the correct option is 'Carbon reduction cycle'.