Ribulose bisphosphate

Definition

Ribulose bisphosphate (RuBP) is a five-carbon sugar phosphate molecule that plays a crucial role in the Calvin Cycle, the process by which plants convert carbon dioxide into glucose during photosynthesis. RuBP acts as the carbon dioxide acceptor and is essential for the fixation of carbon in the cycle, enabling the production of organic molecules that provide energy for the plant.

5 Must Know Facts For Your Next Test

1. Ribulose bisphosphate has a chemical formula of C5H10O5P and is essential for the initial step of the Calvin Cycle.
2. The reaction between ribulose bisphosphate and carbon dioxide is catalyzed by the enzyme RuBisCO, which is one of the most abundant proteins on Earth.
3. After carbon fixation occurs, ribulose bisphosphate is converted into a six-carbon intermediate that quickly splits into two molecules of 3-phosphoglycerate (3-PGA).
4. Ribulose bisphosphate must be regenerated in order for the Calvin Cycle to continue; this regeneration process allows for the continuous fixation of carbon dioxide.
5. Inadequate levels of ribulose bisphosphate can limit the overall rate of photosynthesis and affect plant growth and productivity.

Review Questions

• How does ribulose bisphosphate contribute to the process of carbon fixation in the Calvin Cycle?
  • Ribulose bisphosphate is integral to carbon fixation because it serves as the primary acceptor of carbon dioxide during the Calvin Cycle. When carbon dioxide enters the cycle, it reacts with ribulose bisphosphate, facilitated by the enzyme RuBisCO. This reaction forms a transient six-carbon compound that immediately breaks down into two molecules of 3-phosphoglycerate (3-PGA), marking the beginning of converting inorganic carbon into organic compounds.
• Discuss the role of RuBisCO in relation to ribulose bisphosphate and its significance in photosynthesis.
  • RuBisCO is an enzyme that plays a critical role in photosynthesis by catalyzing the reaction between ribulose bisphosphate and carbon dioxide. This reaction is vital for initiating the Calvin Cycle, as it allows for the incorporation of atmospheric carbon into organic molecules. RuBisCO's efficiency affects the overall rate of photosynthesis; despite being abundant, it can be relatively slow and sometimes inefficient due to competing reactions with oxygen, which can hinder plant growth under certain conditions.
• Evaluate how alterations in ribulose bisphosphate levels can impact plant physiology and agricultural productivity.
  • Alterations in ribulose bisphosphate levels can significantly impact plant physiology by influencing the rate of photosynthesis. When RuBP levels are high, plants can efficiently fix carbon dioxide and produce carbohydrates necessary for growth. However, if RuBP is limited due to environmental stresses or nutrient deficiencies, carbon fixation slows down, leading to reduced glucose production and energy availability. This reduction not only affects plant health but can also have cascading effects on agricultural productivity, making it essential to manage growing conditions to maintain optimal RuBP levels.

Related terms

Carbon Fixation: The process of converting inorganic carbon dioxide into organic compounds during photosynthesis, primarily occurring in the Calvin Cycle.

RuBisCO: An enzyme that catalyzes the reaction between ribulose bisphosphate and carbon dioxide, facilitating the first step of the Calvin Cycle.

Glyceraldehyde-3-phosphate (G3P): A three-carbon sugar produced in the Calvin Cycle that serves as a precursor for glucose and other carbohydrates.