Question

In an atmosphere devoid of \(\mathrm{CO}_{2}\) but rich in \(\mathrm{O}_{2}\), the oxygenase activity of rubisco disappears. Why?

Short answer

Without CO2, rubisco cannot perform oxygenase activity effectively.

Step-by-step solution

Understanding Rubisco's Function

Rubisco, or Ribulose-1,5-bisphosphate carboxylase/oxygenase, is an enzyme that catalyzes two types of reactions: carboxylation (with CO2) and oxygenation (with O2). In photosynthesis, it's responsible for fixing carbon dioxide.

Analyzing Conditions Without CO2

In an environment without carbon dioxide, rubisco cannot perform its carboxylase activity, as there is no CO2 available for the carboxylation reaction.

Explaining Oxygenase Activity

Rubisco's second activity is as an oxygenase, using oxygen (O2). However, this activity only occurs when both O2 is present and CO2 concentration is low. Despite high O2, the lack of CO2 disrupts the balance needed for the oxygenase function to occur.

Conclusion on Oxygenase Activity Cessation

Without CO2, rubisco's configuration might not favor the binding of O2, or other regulatory mechanisms dependent on CO2 presence might inhibit its oxygenase activity. Thus, its oxygenase activity disappears.

Key concepts

Oxygenase Activity

The oxygenase activity of rubisco is a fascinating aspect of this enzyme's dual functionality. Rubisco, or Ribulose-1,5-bisphosphate carboxylase/oxygenase, is a key enzyme in the plant world. It can bind with both carbon dioxide (CO2) and oxygen (O2), performing two distinct types of reactions.

• Dual Role: Rubisco's primary function is to fix carbon during the process of photosynthesis by participating in the carboxylation reaction. However, it can also perform oxygenation, which is where the oxygenase activity comes in.
• Oxygenation Reaction: During this reaction, rubisco binds with O2, leading to the formation of phosphoglycolate. This process does not contribute to sugar production and can sometimes be seen as counterproductive.

Oxygenase activity is typically a backup option when CO2 levels are low, meaning rubisco can settle for O2 if necessary. However, in an environment entirely devoid of CO2, rubisco might not efficiently engage in oxygenase activity even if O2 is abundant. This implies that some presence of CO2 is crucial as a regulatory mechanism for rubisco functionality.

Carboxylation Reaction

The carboxylation reaction is central to the vital role rubisco plays in the photosynthesis process. During this reaction, rubisco facilitates the addition of CO2 to ribulose-1,5-bisphosphate (RuBP), resulting in the production of 3-phosphoglycerate (3-PGA).

• Key Role: Carboxylation is critical for synthesizing organic compounds that plants need to grow. Through this reaction, CO2 is effectively fixed into a form usable by the plant.
• Photosynthesis Core: This reaction is a primary step in the Calvin cycle, the set of chemical reactions that occur in chloroplasts during photosynthesis. Without carboxylation, plants cannot synthesize the sugars necessary for energy and growth.

If carbon dioxide is absent, rubisco's carboxylation activity cannot occur, as CO2 is the key substrate for this reaction. Thus, a CO2-rich environment is crucial for the carboxylation reaction and overall effective photosynthesis.

Photosynthesis Process

Photosynthesis is the remarkable process by which plants, algae, and some bacteria convert light energy into chemical energy, primarily in the form of glucose. Rubisco plays an essential role in this process.

• Light Absorption: Photosynthesis begins with light-dependent reactions wherein chlorophyll absorbs sunlight, which is then converted into chemical energy in the form of ATP and NADPH.
• Calvin Cycle involvement: Rubisco operates in the Calvin cycle, where it uses this chemical energy to facilitate the conversion of CO2 into organic sugars through carboxylation.
• Overall Significance: This process is fundamental for life on Earth as it provides the oxygen we breathe and forms the basis of food chains.

In summary, the efficient functioning of rubisco in the photosynthesis process is pivotal to plant life and, by extension, all life forms that depend on plants. Without rubisco's catalyzing action in photosynthesis, plants would not thrive, impacting entire ecosystems.