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How does the Calvin-Benson cycle turn carbon dioxide into sugar?

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Diagram of a tree leaf illustrating photosynthesis, with arrows showing sunlight, water, and carbon dioxide entering the leaf and sugars and oxygen being produced. A person is shown beside the tree to demonstrate the exchange of oxygen and carbon dioxide between plants and animals. — photosynthesis Diagram of photosynthesis showing how water, light, and carbon dioxide are absorbed by a plant to produce oxygen, sugars, and more carbon dioxide.

The Calvin-Benson cycle is a three-stage metabolic pathway occurring in the stroma of the chloroplast that converts carbon dioxide into sugar. The process is driven by energy and electrons provided by ATP and NADPH generated during the light reactions of photosynthesis.1

The cycle proceeds through three distinct stages:

Carboxylation: The enzyme ribulose 1,5-bisphosphate carboxylase (Rubisco) catalyzes the addition of carbon dioxide to the five-carbon compound ribulose 1,5-bisphosphate (RuBP). This creates an unstable six-carbon compound that immediately splits into two molecules of the three-carbon acid PGA.2
Reduction: Using energy from ATP and reducing power from NADPH, the PGA molecules are converted into glyceraldehyde-3-phosphate (Gal3P), a three-carbon sugar phosphate.1
Regeneration: The cycle undergoes a series of reactions to regenerate RuBP, allowing the process to continue.1

For every three molecules of carbon dioxide incorporated, one molecule of Gal3P is produced, which the plant may then convert into starch or export for use as energy.1