Calvin Cycle Overview and Stages

Calvin Cycle Overview

• The Calvin cycle is a crucial part of photosynthesis
• It's a series of biochemical reactions that utilize energy from ATP and NADPH
• It converts inorganic carbon dioxide into organic molecules like glucose.

Calvin Cycle: Stages

• Carbon Fixation: CO₂ combines with RuBP (Ribulose-1,5-bisphosphate)
• An enzyme, RuBisCo, catalyzes this reaction producing a 6 carbon molecule that splits into 2 molecules of 3-PGA (3-phosphoglycerate). This step marks the point at which inorganic carbon is converted to an organic form.
• Reduction phase: ATP and NADPH from the light-dependent reactions are used to convert 3-PGA into G3P (glyceraldehyde-3-phosphate). One molecule of G3P exits the cycle to be used in making glucose; the remaining G3P molecules are recycled.
• Regeneration phase: The remaining G3P molecules are rearranged to regenerate RuBP, enabling the cycle to continue. ATP is also needed for this stage.

Key Players in the Calvin Cycle

• ATP: Provides energy for the cycle’s reactions, particularly in the reduction and regeneration phases.
• NADPH: Provides electrons for the reduction of 3-PGA to G3P.
• RuBisCo: The enzyme that catalyzes the crucial carbon fixation step in the cycle.

Energy Inputs and Output

• Energy inputs: ATP and NADPH are essential for the reduction and regeneration phases.
• Energy output: The net product is G3P, a 3-carbon sugar, used to produce glucose.

Pathways: Types of Photosynthesis

• C3 photosynthesis: This is the most common form
• CO₂ is directly fixed into 3PGA (3-phosphoglycerate). Efficient in cool and moist climates and less effective in hot, dry conditions due to photorespiration.
• C4 photosynthesis: This pathway minimizes photorespiration, allowing plants to thrive in high temperatures and low water availability. CO₂ is initially incorporated into a 4 carbon molecule (oxaloacetate), transported to a different cell type, then released to enter the Calvin Cycle.
• CAM photosynthesis: Plants using this pathway open their stomata at night to take in CO₂ which is stored as an acid. During the day, the stored CO₂ is released into the Calvin cycle, minimizing water loss.

Explore the Calvin cycle, a vital component of photosynthesis. This quiz covers its stages: carbon fixation, reduction, and regeneration, highlighting the biochemical reactions and energy sources involved. Test your knowledge on how inorganic carbon is converted into organic molecules like glucose.