Calvin-benson cycle

Calvin-Benson Cycle

The Calvin-Benson Cycle, also known as the Calvin Cycle or the Light-independent reactions, is a series of biochemical, enzyme-mediated reactions that occur within the chloroplasts of photosynthetic organisms. Named after its discoverers, Melvin Calvin and Andrew Benson, the cycle is a key part of the photosynthesis process, converting carbon dioxide into organic compounds, particularly glucose.

Overview

The Calvin-Benson Cycle takes place in the stroma of the chloroplasts, where it uses the energy stored in ATP and NADPH during the light-dependent reactions of photosynthesis. The cycle is composed of three main stages: carbon fixation, reduction, and regeneration of the starting molecule.

Carbon Fixation

In the first stage, carbon dioxide from the atmosphere is attached to a five-carbon sugar called ribulose bisphosphate (RuBP) by the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). This reaction produces a six-carbon compound that immediately splits into two molecules of 3-phosphoglycerate (3-PGA).

Reduction

The second stage involves the reduction of 3-PGA into glyceraldehyde 3-phosphate (G3P) using ATP and NADPH. Some of the G3P molecules are used to produce glucose and other organic compounds.

Regeneration

In the final stage, the remaining G3P molecules are used to regenerate RuBP, allowing the cycle to continue. This process requires additional ATP molecules.

Significance

The Calvin-Benson Cycle is crucial for life on Earth as it is the primary pathway for the conversion of sunlight energy into chemical energy stored in glucose and other organic compounds. This process not only provides energy for plants but also forms the basis of the food chain for other organisms.

See Also

• Photosynthesis
• Light-dependent reactions
• Carbon fixation
• Melvin Calvin
• Andrew Benson