Carboxylation Phase
The initial step of CO2 fixation where RuBP combines with CO2, catalyzed by the enzyme RuBisCO, forming two molecules of 3-PGA.
What is Carboxylation Phase?
The addition of carbon dioxide to a molecule.
Key formula / rule: Carboxylation Reaction
Key points
- Understand the role of the carboxylation phase in the Calvin cycle.
- Identify the substrate (RuBP) and enzyme (RuBisCO) involved.
- Recognize the immediate product (3-PGA) and its significance.
- Explain the process of CO2 fixation in C3 plants.
Common exam trap
Confusing RuBP with RuBisCO.
Definitions
- Term
Carboxylation
- Meaning
The addition of carbon dioxide to a molecule.
- Term
RuBisCO
- Meaning
Ribulose-1,5-bisphosphate carboxylase/oxygenase, the enzyme that catalyzes the first step of carbon fixation in photosynthesis.
- Term
3-Phosphoglycerate (3-PGA)
- Meaning
A three-carbon molecule that is the first stable product of carbon fixation in the Calvin cycle.
- Term
Ribulose-1,5-bisphosphate (RuBP)
- Meaning
A five-carbon sugar molecule that acts as the primary CO2 acceptor in the Calvin cycle.
Learning objectives
Understand the role of the carboxylation phase in the Calvin cycle.
Identify the substrate (RuBP) and enzyme (RuBisCO) involved.
Recognize the immediate product (3-PGA) and its significance.
Explain the process of CO2 fixation in C3 plants.
Formulae
- Name
Carboxylation Reaction
- Note
This is a simplified representation; the reaction involves the enzyme RuBisCO and an unstable intermediate.
- Expression
Ribulose-1,5-bisphosphate + CO2 → 2 x 3-Phosphoglycerate
Prerequisites
Photosynthesis: Overall process and location.
Chloroplast structure and function.
Enzymes: Role and specificity.
Basic organic molecules: Carbon compounds.
Common mistakes
Confusing RuBP with RuBisCO.
Forgetting that the initial product breaks down into two molecules.
Misidentifying the enzyme or substrate.
Not recognizing that this is the *first* step of CO2 fixation.
Keywords
Calvin Cycle
C3 Pathway
Carboxylation
CO2 Fixation
RuBisCO
RuBP
3-PGA
Photosynthesis
Stroma
Chloroplast
Practice preview
Which enzyme catalyzes the carboxylation of RuBP during the Calvin cycle?…
easy
Which enzyme catalyzes the carboxylation of Ribulose-1,5-bisphosphate (RuBP) during the Calvin cycle?…
easy
The product formed immediately after the carboxylation of RuBP in the Calvin cycle is:…
easy