The Calvin Cycle: Detailed Process Analysis

The Calvin cycle operates through three interconnected phases that work together to convert carbon dioxide into useful sugar molecules. The process begins in the stroma of chloroplasts, where the Role of ATP and NADPH in Calvin cycle becomes crucial for energy provision and reduction reactions.

Definition: The Calvin cycle is a metabolic pathway that uses energy from ATP and reducing power from NADPH to convert CO₂ into sugar molecules.

Highlight: The cycle requires three ATP molecules and two NADPH molecules to fix one CO₂ molecule into organic matter.

Vocabulary: Rubisco (Ribulose-1,5-bisphosphate carboxylase/oxygenase) - The primary enzyme responsible for carbon fixation in the Calvin cycle.

Example: During carbon fixation, Rubisco attaches each CO₂ molecule to ribulose bisphosphate (RuBP), forming an unstable six-carbon intermediate that quickly splits into two three-carbon molecules.

The three phases of the Calvin cycle are:

1. Carbon Fixation: CO₂ is attached to RuBP by Rubisco, forming an unstable six-carbon compound that splits into two molecules of 3-phosphoglycerate.

2. Reduction: 3-phosphoglycerate is converted to G3P through phosphorylation by ATP and reduction by NADPH.

3. RuBP Regeneration: Five G3P molecules are rearranged using three ATP molecules to regenerate three RuBP molecules, allowing the cycle to continue.

Quote: "The Calvin Cycle occurs in the stroma, uses ATP + NADPH to convert CO₂ to the sugar, G3P and returns ADP, inorganic phosphates and NADP+ to light reactions."