Energy and Reducing Power Requirements
Quantification of ATP and NADPH consumed for each turn of the Calvin cycle and for the synthesis of one glucose molecule.
What is Energy and Reducing Power Requirements?
The light-independent reactions of photosynthesis where carbon dioxide is fixed and reduced to form carbohydrates, occurring in the stroma of chloroplasts.
Key formula / rule: ATP and NADPH requirement per 3 CO2 fixation (net G3P production)
Key points
- Quantify the ATP and NADPH required for the fixation of three CO2 molecules.
- Determine the ATP and NADPH requirement for the synthesis of one net G3P molecule.
- Calculate the total ATP and NADPH consumed for the production of one glucose molecule.
- Understand the role of ATP and NADPH in different stages of the Calvin cycle.
Common exam trap
Confusing the number of ATP and NADPH required per CO2 molecule versus per G3P or glucose molecule.
Definitions
- Term
Calvin Cycle
- Meaning
The light-independent reactions of photosynthesis where carbon dioxide is fixed and reduced to form carbohydrates, occurring in the stroma of chloroplasts.
- Term
Glyceraldehyde-3-phosphate (G3P)
- Meaning
A three-carbon sugar phosphate that is the direct product of the Calvin cycle; two molecules of G3P can be combined to form glucose.
- Term
ATP (Adenosine Triphosphate)
- Meaning
The primary energy currency of the cell, used to power various cellular processes, including the Calvin cycle.
- Term
NADPH (Nicotinamide Adenine Dinucleotide Phosphate)
- Meaning
An electron carrier that provides reducing power (electrons) for biosynthetic reactions, such as the reduction step in the Calvin cycle.
Learning objectives
Quantify the ATP and NADPH required for the fixation of three CO2 molecules.
Determine the ATP and NADPH requirement for the synthesis of one net G3P molecule.
Calculate the total ATP and NADPH consumed for the production of one glucose molecule.
Understand the role of ATP and NADPH in different stages of the Calvin cycle.
Formulae
- Name
ATP and NADPH requirement per 3 CO2 fixation (net G3P production)
- Note
This is the fundamental stoichiometric requirement for one turn of the cycle producing a net output.
- Expression
9 ATP, 6 NADPH
- Name
ATP and NADPH requirement per Glucose molecule synthesis
- Note
Since one glucose molecule requires two G3P molecules, the requirement is doubled.
- Expression
18 ATP, 12 NADPH
Prerequisites
Light-dependent reactions of photosynthesis (ATP and NADPH production)
Enzymes involved in the Calvin cycle (e.g., RuBisCO)
Basic understanding of chemical energy (ATP) and reducing power (NADPH)
Common mistakes
Confusing the number of ATP and NADPH required per CO2 molecule versus per G3P or glucose molecule.
Forgetting that ATP is also required for the regeneration of RuBP.
Incorrectly calculating the total ATP and NADPH for a glucose molecule (which requires two G3P).
Assuming that all ATP and NADPH produced in light reactions are used solely for the Calvin cycle.
Keywords
Calvin Cycle
C3 Pathway
Photosynthesis
ATP
NADPH
G3P
Glucose Synthesis
Carbon Fixation
Reduction
Regeneration
RuBP
RuBisCO
Practice preview
In the Calvin cycle, which step directly consumes ATP and NADPH?…
easy
How many molecules of ATP and NADPH are consumed in the Calvin cycle for the fixation of one molecule of CO2?…
easy
What is the total requirement of ATP and NADPH for the synthesis of one molecule of glucose (C6H12O6) via the Calvin cycle?…
easy