Limited access

Upgrade to access all content for this subject

The photosynthetic enzyme RuBisCO (ribulose-1,5-bisphosphate carboxylase oxygenase) is one of the most important and abundant proteins on earth. This dual function enzyme first evolved under anaerobic conditions. In land plants, the enzyme consists of 8 large subunits and 8 small subunits with a molecular mass of about 540 KDa.

Use your understanding of photosynthesis and Rubisco to determine which of the following statements is UNTRUE regarding RuBisCO.


The RuBisCO protein is very abundant in plant leaves largely because the enzyme is extremely inefficient in land plants.


The dual function of RuBisCO refers to the enzyme catalyzing both ${ CO }_{ 2 }$ fixation and ${ O }_{ 2 }$ fixation, with both gases competing for the same binding site.


In land plants, the RuBisCO large subunit is encoded by the chloroplast genome, whereas the small subunit is nuclear encoded.


RuBisCO is the primary carboxylase in both ${ C }_{ 3 }$ and ${ C }_{ 4 }$ plants, whereas phosphoenolpyruvate (PEP) carboxylase is the active carboxylase in Crassulacean acid metabolism (CAM) plants (e.g., cacti).


RuBisCO is only functional in the light and is a rate-limiting reaction of the Calvin-Benson-Bassham ${ CO }_{ 2 }$ fixation pathway.

Select an assignment template