NEETBotanyPhotosynthesis in Higher Plants
In an experiment with isolated chloroplasts from a C₃ plant, it is observed that as the ratio of O₂ to CO₂ in the surrounding medium increases, the formation of a 2-carbon compound increases while the overall sugar yield drops. Which specific property of the primary carboxylating enzyme explains this phenomenon?
Options
- ACompetitive binding of O₂ and CO₂ at the same active site
- BAllosteric inhibition of the enzyme's activity by high concentrations of O₂
- CNon-competitive inhibition of the enzyme by the newly formed 2-carbon compound
- DIrreversible denaturation of the enzyme's active site at elevated O₂ levels
Correct answer
A. Competitive binding of O₂ and CO₂ at the same active site
Step-by-step solution
The primary carboxylating enzyme in C₃ plants is RuBisCO (Ribulose bisphosphate carboxylase-oxygenase). RuBisCO has a single active site that can bind to both CO₂ and O₂ . The binding of these two gases is competitive. When the ratio of O₂ to CO₂ increases, O₂ successfully competes with CO₂ for the active site. This shifts the enzyme's function towards its oxygenase activity. As a result, RuBP is oxygenated to form a 3-carbon compound (phosphoglycerate) and a 2-carbon compound (phosphoglycolate), initiating the pho