Reduction phase

Definition

The reduction phase is a key stage in the Calvin cycle where ATP and NADPH are utilized to convert 3-phosphoglycerate (3-PGA) into glyceraldehyde-3-phosphate (G3P). This process is crucial for fixing carbon dioxide into organic molecules, allowing plants to produce sugars that serve as an energy source for growth and metabolism.

5 Must Know Facts For Your Next Test

1. During the reduction phase, each molecule of 3-PGA is phosphorylated by ATP and then reduced by NADPH, resulting in the formation of G3P.
2. For every three molecules of carbon dioxide that enter the Calvin cycle, six G3P molecules are produced, but only one G3P molecule exits the cycle to be used in glucose synthesis.
3. The reduction phase is essential for regenerating ribulose bisphosphate (RuBP), enabling the cycle to continue and fix more carbon dioxide.
4. The overall reaction in the reduction phase highlights the conversion of light energy stored as ATP and NADPH into chemical energy stored in carbohydrates.
5. Understanding the reduction phase helps illustrate how plants convert inorganic carbon into organic forms, which is fundamental for life on Earth.

Review Questions

• How does the reduction phase contribute to the overall function of the Calvin cycle?
  • The reduction phase is essential in transforming 3-phosphoglycerate (3-PGA) into glyceraldehyde-3-phosphate (G3P) using ATP and NADPH. This conversion is critical as it fixes carbon dioxide into organic molecules, allowing plants to produce sugars. These sugars serve as a primary energy source for various cellular processes, linking the light-dependent reactions with carbohydrate synthesis.
• What role do ATP and NADPH play during the reduction phase of the Calvin cycle?
  • ATP and NADPH are vital for the reduction phase as they provide the energy and reducing power needed to convert 3-PGA into G3P. Specifically, ATP phosphorylates 3-PGA, activating it for reduction, while NADPH donates electrons to reduce 1,3-bisphosphoglycerate into G3P. This process effectively harnesses energy captured from sunlight to drive the formation of carbohydrates from carbon dioxide.
• Evaluate the importance of G3P produced in the reduction phase in relation to plant metabolism and energy storage.
  • Glyceraldehyde-3-phosphate (G3P) produced during the reduction phase is critical for plant metabolism as it serves as a building block for glucose and other carbohydrates. These carbohydrates can be used immediately for energy or stored as starch for later use. The ability to convert carbon dioxide into G3P reflects how plants maintain energy balance and contribute to ecosystem productivity, emphasizing their role in global carbon cycling and energy flow.

Related terms

Calvin cycle: A series of biochemical reactions occurring in the stroma of chloroplasts that converts carbon dioxide and other compounds into glucose, driven by light energy.

NADPH:

A reducing agent produced during the light reactions of photosynthesis, which provides the necessary electrons for the reduction phase.

G3P: Glyceraldehyde-3-phosphate, a three-carbon sugar produced during the reduction phase of the Calvin cycle, which can be used to form glucose and other carbohydrates.