Concept 10.4: The Calvin cycle uses the chemical energy of ATP and NADPH to reduce carbon dioxide to sugar

Flashcards from Concept 10.4 of Pearson's Campbell Biology, Twelfth Edition.

Calvin cycle

An anabolic process within the stroma of the chloroplast that builds sugar from smaller molecules using ATP with the reducing power of electrons carried by NADPH

• Has the three phrases of carbon fixation, reduction, and regeneration of the CO₂ acceptor (RuBP)

• Consumes 9 ATP and 6 NADPH overall to make 1 G3P molecule for other molecular synthesis processes, which are regenerated with light reactions

Glyceraldehyde 3-phosphate (G3P)

The sugar that is produced from carbon that enters as CO₂

• One of these requires three complete cycles to fix three CO₂ molecules

Carbon fixation

The binding of CO₂ to a five-carbon sugar named ribulose biphosphate, catalyzed by RuBP carboxylase-oxygenase (rubisco)

• This is then split into two molecules of 3-phosphoglycerate for each CO₂ fixed

Rubisco

Enzyme that catalyzes the binding of CO₂ to ribulose biphosphate in carbon fixation

Reduction

The phosphorylation of each molecule of 3-phosphoglycerate by six ATP and six NADPH to produce a G3P sugar

• Results in a 3:6 CO₂ input to G3P output ratio

• Only one G3P molecule can be counted as a net gain of carbohydrate as it is passed on, the rest remain to regenerate the CO₂ acceptor RuBP

Regeneration of RuBP

The rearrangement of the five molecules of G3P in a complex series of reactions to yield three molecules of RuBP

• This uses three additional ATP molecules