Question

Which enzyme catalyzes the fixation of CO2?

Pyruvate decarboxylase

Citrate synthase

Ribulose 1,5 bisphosphate carboxylase/oxygenase

Phosphoenolpyruvate carboxykinase

Succinate dehydrogenase

Answer 1

Enzyme catalyzes the fixation of CO2 is

Ribulose 1,5 bisphosphate carboxylase/oxygenase or RUBISCO.

RUBISCO catalyzes the carboxylation process (fixing atmospheric CO2) of ribulose-1,5-bisphosphate (RUBP) to produce 3-phosphoglycerate which is used to produce larger molecules such as glucose.

Pyruvate decarboxylase: it catalyzes the decarboxylation of pyruvate and does not fix the CO2

Citrate synthase: In Krebs cycle, this enzyme form  citrate by condentation of acetyl-CoA and oxaloacetate.

Phosphoenolpyruvate carboxykinase: This enzyme decarboxylates the CO2 from oxaloacetate and produce phosphoenolpyruvate and not related to the carbon fixing.

Succinate dehydrogenase: This enzyme is responsible for the oxidation of succinate into fumarate in the Krebs cycle.

So all of these options are wrong except Ribulose 1,5 bisphosphate carboxylase/oxygenase or RUBISCO.