Calvin Cycle (C3 Pathway)
Carboxylation, reduction and regeneration with RuBisCO at the centre. (Biology › Photosynthesis in Higher Plants, NEET UG syllabus.)
What is Calvin Cycle (C3 Pathway)?
The metabolic pathway in the stroma of chloroplasts where atmospheric carbon dioxide is fixed and converted into glucose, using ATP and NADPH from the light-dependent reactions.
Key formula / rule: Overall Stoichiometry for 1 Glucose
Key points
- Describe the three main stages of the Calvin cycle (carboxylation, reduction, regeneration).
- Identify the key enzyme RuBisCO and its specific role in carbon fixation.
- List the inputs (CO2, ATP, NADPH) and outputs (G3P, ADP, NADP+) of the Calvin cycle.
- Explain the energy requirements (ATP and NADPH) for synthesizing one molecule of glucose.
Common exam trap
Confusing the Calvin cycle (C3 pathway) with the C4 pathway or CAM pathway.
Definitions
- Term
Calvin Cycle (C3 Pathway)
- Meaning
The metabolic pathway in the stroma of chloroplasts where atmospheric carbon dioxide is fixed and converted into glucose, using ATP and NADPH from the light-dependent reactions.
- Term
RuBisCO
- Meaning
Ribulose-1,5-bisphosphate carboxylase/oxygenase, the enzyme that catalyzes the carboxylation of RuBP with CO2, initiating the Calvin cycle.
- Term
RuBP (Ribulose-1,5-bisphosphate)
- Meaning
A five-carbon sugar that acts as the primary CO2 acceptor in the Calvin cycle.
- Term
3-PGA (3-Phosphoglycerate)
- Meaning
The first stable three-carbon compound formed after CO2 fixation in the Calvin cycle.
- Term
G3P (Glyceraldehyde-3-phosphate)
- Meaning
A three-carbon sugar phosphate that is the direct product of the reduction phase and can be used to synthesize glucose or regenerate RuBP.
- Term
Carboxylation
- Meaning
The initial step of the Calvin cycle where CO2 is incorporated into an organic molecule (RuBP).
- Term
Reduction
- Meaning
The stage in the Calvin cycle where 3-PGA is converted to G3P using ATP and NADPH.
- Term
Regeneration
- Meaning
The final stage of the Calvin cycle where RuBP is reformed from G3P, requiring ATP, to continue the cycle.
Learning objectives
Describe the three main stages of the Calvin cycle (carboxylation, reduction, regeneration).
Identify the key enzyme RuBisCO and its specific role in carbon fixation.
List the inputs (CO2, ATP, NADPH) and outputs (G3P, ADP, NADP+) of the Calvin cycle.
Explain the energy requirements (ATP and NADPH) for synthesizing one molecule of glucose.
Understand the significance of the Calvin cycle in converting inorganic carbon into organic compounds.
Relate the Calvin cycle to the overall process of photosynthesis.
Formulae
- Name
Overall Stoichiometry for 1 Glucose
- Note
This represents the net consumption of inputs and production of outputs for the synthesis of one glucose molecule in the Calvin cycle.
- Expression
6 CO2 + 18 ATP + 12 NADPH + 12 H2O → C6H12O6 + 18 ADP + 18 Π + 12 NADP+ + 6 H+
Prerequisites
Basic understanding of photosynthesis (light and dark reactions).
Knowledge of ATP and NADPH as energy carriers and reducing agents.
Familiarity with the structure of chloroplasts (stroma, thylakoids).
Basic concepts of carbon fixation and organic molecules.
Common mistakes
Confusing the Calvin cycle (C3 pathway) with the C4 pathway or CAM pathway.
Forgetting that while it's 'light-independent', it still requires products (ATP, NADPH) from the light-dependent reactions.
Incorrectly identifying the CO2 acceptor (RuBP) or the first stable product (3-PGA).
Miscalculating the ATP and NADPH requirements for synthesizing one molecule of glucose.
Not understanding the importance of the regeneration phase for cycle continuity.
Keywords
Calvin Cycle
C3 Pathway
Photosynthesis
Dark Reaction
Stroma
RuBisCO
RuBP
3-PGA
G3P
Carboxylation
Reduction
Regeneration
ATP
NADPH
Carbon Fixation
Glucose
Practice preview
How many molecules of ATP and NADPH are required to fix one molecule of CO2 in the Calvin cycle?…
medium
What is the correct sequence of the three main stages of the Calvin cycle?…
medium
What is the primary fate of the glyceraldehyde-3-phosphate (G3P), also known as triose phosphate, produced during the reduction phase of the Calvin cycle?…
hard