5.3 The Calvin Cycle

This flashcard set covers the key terms, molecular components, and chemical stages of the Calvin cycle as described in the Concepts of Biology text.

Calvin cycle

The reactions of photosynthesis that use the energy stored by the light-dependent reactions to form glucose and other carbohydrate molecules.

Calvin-Benson cycle

An alternative name for the Calvin cycle, including the name of scientist Andrew Benson.

Stroma

The site of the Calvin cycle reactions in the chloroplast where sugar is synthesized.

Stomata

Openings in the leaf through which carbon dioxide ($CO_2$) enters and diffuses into mesophyll cells.

Ribulose bisphosphate (RuBP)

A molecule that has five atoms of carbon and a phosphate group on each end, used to initiate the Calvin cycle.

RuBisCO

The enzyme that catalyzes a reaction between $CO_2$ and RuBP to form a six-carbon compound.

Carbon fixation

The process of "fixing" $CO_2$ from its inorganic form into organic molecules.

Reduction reaction

A type of reaction involving the gain of an electron by an atom or molecule.

3-PGA

A three-carbon compound that is converted into G3P using energy from ATP and NADPH.

G3P

A three-carbon compound formed in the reduction stage; some molecules leave the cycle to form glucose while others regenerate RuBP.

Six turns

The number of turns of the Calvin cycle required to fix six carbon atoms to make one carbohydrate molecule such as glucose ($C_6H_{12}O_6$).

Regeneration

The third stage of the Calvin cycle where remaining G3P molecules and ATP are used to reform RuBP.

Cyanobacteria

A type of photosynthetic prokaryote that lacks membrane-bound organelles but uses infoldings of the plasma membrane for photosynthesis.

Photosynthesis reaction

$$6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$$

Cellular respiration reaction

$$6O_2 + C_6H_{12}O_6 \rightarrow 6CO_2 + 6H_2O$$

Energy requirement for one glucose

$12$ ATP molecules and $12$ NADPH molecules in the reduction step, and $6$ ATP molecules in the regeneration step.