Photosynthesis and the Calvin Cycle

Vocabulary terms and definitions covering the mechanisms of C3 photosynthesis, chloroplast structure, light-dependent reactions, and the phases of the Calvin cycle.

C3 photosynthesis

The most common version of photosynthesis which uses anabolic redox reactions to generate glyceraldehyde 3-phosphate (G3P).

Glyceraldehyde 3-phosphate (G3P)

An important precursor to the carbohydrate glucose ($C_6H_{12}O_6$) and other biomolecules; two molecules of this are required to create one molecule of glucose.

Chloroplasts

Specialized organelles located within the cells of green plant tissues where photosynthesis occurs.

Mesophyll

A type of leaf tissue found between layers of epidermis and a waxy cuticle where chloroplasts are found in abundance.

Stomata

Openings in the leaf that allow for the diffusion of $CO_2$ and $O_2$ to and from chloroplasts through the protective epidermis and cuticle.

Thylakoids

Membrane-bound sacs inside the chloroplast where light-dependent reactions take place.

Granum

A stack of thylakoids; multiple stacks are referred to as grana.

Lumen

The internal space of each thylakoid, also referred to as the thylakoid space.

Stroma

The fluid-filled space surrounding the thylakoids where light-independent reactions (Calvin cycle) take place.

Photosystem II (PS II)

The initial phase of photosynthesis in which water molecules are broken down into hydrogen ions ($H^+$), electrons ($e^-$), and oxygen.

ATP-synthase

An enzyme that facilitates chemiosmosis by allowing $H^+$ to flow back into the stroma, joining ADP with phosphate to form ATP.

Photosystem I (PS I)

The second phase of photosynthesis where electrons from Photosystem II are re-energized by sunlight and transferred to the enzyme NADP-reductase.

NADPH

A reduced coenzyme produced when the enzyme NADP-reductase attaches electrons from Photosystem I and $H^+$ from the stroma to NADP+.

Calvin cycle

Light-independent reactions occurring in the stroma that begin with the intake of atmospheric $CO_2$ to eventually yield G3P.

Carbon Fixation

The first phase of the Calvin cycle where three molecules of $CO_2$ are combined with three molecules of RuBP by the enzyme RubisCO.

RuBP

A five-carbon molecule ($C_5$) used to restart the Calvin cycle after being combined with $CO_2$.

RubisCO

The enzyme responsible for combining CO2 and RuBP during the Carbon Fixation phase of the Calvin cycle.

3PG (3-PGA)

Six three-carbon molecules produced immediately after the unstable six-carbon intermediate metabolite breaks down during Carbon Fixation.

Reduction (Calvin Cycle Phase)

The second phase of the Calvin cycle where six molecules of ATP and NADPH are used to reduce 3PG into BPG and then into G3P.

Regeneration (Calvin Cycle Phase)

The third phase of the Calvin cycle where five remaining molecules of G3P are converted back into RuBP using three molecules of ATP.