What is the Difference Between RuBP and RuBisCO

The main difference between RuBP and RuBisCO is that RuBP is the organic molecule that starts the Calvin cycle and regenerates at the end or at stage 3 of the cycle, whereas RuBisCO is the enzyme that incorporates carbon dioxide into RUBP, reducing the organic molecule in stage 1 of the Calvin cycle.

RuBP and RuBisCO are two types of compounds that occur in the Calvin cycle in photosynthesis. The Calvin cycle is the set of reactions that uses the energy stored by the light-dependent reactions, forming glucose and other carbohydrate molecules.       

Key Areas Covered

1. What is RuBP
     – Definition, Features, Function
2. What is RuBisCO
     – Definition, Features, Function
3. Similarities Between RuBP and RuBisCO
    – Outline of Common Features
4. Difference Between RuBP and RuBisCO
     – Comparison of Key Differences

Key Terms

RuBisCO, RuBP

What is RuBP

RuBP or ribulose- 1,5-bisphosphate is the principal carbon dioxide acceptor of plants. It is also an important organic substance involved in photosynthesis. RuBP occurs in all life forms, including Bacteria, Archaea, and Eukarya. Moreover, RuBP is the first molecule of the Calvin cycle that incorporates carbon dioxide molecules. Generally, atmospheric carbon dioxide molecules couple into RuBP, generating a 6-carbon molecule. In addition, RuBP is a 5-carbon molecule. RuBP is also the major compound of the dark reaction of photosynthesis.

Figure 1: RuBP

Furthermore, after the incorporation of carbon dioxide into RuBP, the resultant 6-carbon molecule is immediately broken down into two 3-carbon molecules. These molecules are PGA (phosphoglycerate). This reaction is also known as carbon fixation. Here, some PGA is responsible for regenerating RuBP, while others are converted into sugars. Additionally, less RuBP regeneration increases the efficiency of crop productivity.    

What is RuBisCO

RuBisCO or ribulose-1,5-bisphosphate carboxylase/oxygenase is the enzyme responsible for the major step of carbon fixation. In carbon fixation, atmospheric carbon dioxide converts into carbohydrates during the dark reaction of photosynthesis. The main function of the dark reaction of photosynthesis is to use the energy fixed in the light reaction of photosynthesis to produce carbohydrates. Generally, RuBisCO is the most abundant enzyme on earth.

Figure 2: RuBisCO

Moreover, RuBisCO is a biologically important enzyme that catalyzes the primary chemical reaction through which inorganic carbon enters the biosphere. PGA molecules that form by the carbon fixation convert into G3P using the energy stored in the ATP and NADPH from the light reaction of photosynthesis. They are reduction reactions that gain electrons to the organic molecules. One G3P molecule contributes to the formation of a carbohydrate molecule. Meanwhile, the remaining G3P molecules contribute to the regeneration of RuBP.

Similarities Between RuBP and RuBisCO

• RuBP and RuBisCO are two types of compounds that occur in the Calvin Cycle.
• Moreover, the main function of these molecules is to use the energy stored in the light-dependent reaction of photosynthesis.

Difference Between RuBP and RuBisCO

Definition

RuBP refers to an organic substance that is involved in photosynthesis, notably as the principal CO₂ acceptor in plants, while RuBisCO refers to an enzyme present in plant chloroplasts, involved in fixing atmospheric carbon dioxide during photosynthesis and in oxygenation of the resultant compound during photorespiration.

Importance

RuBP is the organic molecule that starts the Calvin cycle, and it regenerates at the end or at stage 3 of the cycle, while RuBisCO is the enzyme that incorporates carbon dioxide into RuBP, reducing the organic molecule in stage 1 of the Calvin cycle.

Significance

RuBP is an organic molecule, while RuBisCO is an enzyme.

Conclusion                                                       

In brief, RuBP and RuBisCO are two types of compounds that occur in the reactions of the Calvin cycle. Generally, the main function of the Calvin cycle is to use the energy of the light reaction to produce glucose and other organic molecules. RuBP is an organic molecule capable of incorporating carbon dioxide. It regenerates at the end of the Calvin cycle. In comparison, RuBisCO is the enzyme responsible for incorporating carbon dioxide into RuBP. Therefore, the main difference between RuBP and RuBisCO is the type and function.                                              

References:

1. Rye, C., Avissar, Y., Jurukovski, V., Fowler, S., Wise, R., Roush, R., Choi, J., DeSaix, J., Wise, J., Nakano, M., Molnar, C., & Gair, J. “3: The Calvin cycle.” Concepts of Biology 1st Canadian Edition.

Image Courtesy:

1. “RuBP-2D-skeletal” By Benjah-bmm27 – Own work (Public Domain) via Commons Wikimedia
2. “RuBisCO reaction CO2 or O2” By Prithason at Yikrazuul – Own Work (CC BY-SA 3.0) via Commons Wikimedia