Ribulose bisphosphate carboxylase/oxygenase (rubisco)

Definition

Ribulose bisphosphate carboxylase/oxygenase, commonly known as rubisco, is an enzyme that catalyzes the first major step of carbon fixation in the photosynthetic process. It plays a crucial role in converting inorganic carbon dioxide into organic compounds, specifically ribulose bisphosphate (RuBP) into 3-phosphoglycerate during the Calvin cycle. Rubisco is significant in understanding both the C4 and CAM pathways as it directly influences how different plants capture and utilize carbon dioxide efficiently.

5 Must Know Facts For Your Next Test

1. Rubisco is one of the most abundant proteins on Earth, making up a significant portion of the total protein in plant leaves.
2. The enzyme can function as both a carboxylase and an oxygenase, leading to the dual roles of fixing carbon dioxide and producing a wasteful process called photorespiration.
3. In C4 plants, rubisco is located in specialized bundle-sheath cells, which helps minimize oxygen interference by concentrating CO2 around the enzyme.
4. In CAM plants, rubisco activity occurs at night when CO2 is fixed into organic acids, allowing for efficient use of water during the day when stomata are closed.
5. Enhancing rubisco efficiency through genetic engineering is a target for increasing crop yields and improving food security in a changing climate.

Review Questions

• How does rubisco function differently in C4 and CAM plants compared to C3 plants?
  • In C4 and CAM plants, rubisco plays a more efficient role in carbon fixation by minimizing the occurrence of photorespiration. In C4 plants, carbon dioxide is first fixed into a four-carbon compound before entering the Calvin cycle, which increases CO2 concentration around rubisco in bundle-sheath cells. In CAM plants, rubisco operates at night when CO2 is captured as organic acids, allowing these plants to conserve water during the day while still fixing carbon effectively.
• What are the implications of rubisco's dual activity as a carboxylase and oxygenase for plant photosynthesis?
  • Rubisco's ability to act as both a carboxylase and an oxygenase leads to photorespiration, a process that can significantly reduce the efficiency of photosynthesis. When rubisco fixes oxygen instead of carbon dioxide, it results in the loss of carbon that could otherwise be used for growth and energy production. This duality has prompted evolution in some plants to develop C4 and CAM pathways to enhance photosynthetic efficiency under specific environmental conditions.
• Evaluate the potential benefits of engineering rubisco to improve agricultural productivity in light of climate change.
  • Engineering rubisco could potentially increase agricultural productivity by enhancing its efficiency in carbon fixation and reducing photorespiration losses. This could lead to higher crop yields, especially in environments with elevated temperatures and CO2 levels due to climate change. Improving rubisco's performance may also allow plants to use water resources more efficiently, crucial for sustaining agriculture in arid regions. Such advancements could contribute significantly to food security challenges faced globally.

Related terms

Calvin Cycle:

A series of biochemical reactions that take place in the chloroplasts during photosynthesis, where carbon dioxide is fixed into glucose using energy from ATP and NADPH.

C4 Photosynthesis:

A carbon fixation pathway that evolved in some plants to enhance efficiency by minimizing photorespiration, where rubisco can mistakenly fix oxygen instead of carbon dioxide.

Photorespiration:

A process where rubisco catalyzes the reaction of oxygen with ribulose bisphosphate instead of carbon dioxide, leading to a decrease in photosynthetic efficiency.