Page 171 - Algae Anatomy, Biochemistry, and Biotechnology

154 Algae: Anatomy, Biochemistry, and Biotechnology

FIGURE 3.9 Schematic drawing of the three phases of CBB cycle.

a huge amount of their available nitrogen into making this one protein. As a result, RuBisCO is
the most abundant protein in the biosphere. The resulting 6-carbon product splits into two
identical 3-carbon products. These products are 3-phosphoglycerate, or simply 3-PG. At this
point in the cycle, CO 2 has been “fixed” into an organic product but no energy has been added
to the molecule.

Reduction

The second step in the Calvin cycle is the reduction of 3-PG to the level of carbohydrate. This reac-
tion occurs in two steps: (1) phosphorylation of 3-PG by ATP to form a 1,3-biphosphoglycerate
(1,3-BPG) and (2) reduction of 1,3-BPG by NADPH to form glyceraldehyde-3-phosphate (G3P),
a simple 3-carbon carbohydrate, and its isomers collectively called triose phosphates. This reaction
requires both ATP and NADPH, the high energy chemical intermediates formed in the light
reactions.
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The NADP and ADP formed in this process return to the thylakoids to regenerate NADPH and
ATP in the light reactions.