C3 Pathway
C3 carbon fixation is one of the three metabolic pathways involved in carbon fixation in photosynthesis; the others are C4 and CAM. The plants that contain C3 photosynthesis are called C3 plants, and they include 95% of all plants on earth. Plants that exhibit this process depend on those areas where sunlight intensity is moderate, temperature is moderate, and CO2 is around 200 ppm or higher.
- Carboxylation: In C3 fixation, ribulose 1,5-bisphosphate (RuBP) is carboxylated to form three-carbon compounds by activity of RuBisCO. Then, the CO2 molecule condenses with RuBP to produce a transient six-carbon intermediate that hydrolyzes into two molecules of 3-phosphoglycerate (PGA).
- Reduction: PGA is the first stable compound to contain three carbon atoms; this process is called C3 fixation. This reaction leads to the regeneration of ribulose 1,5-bisphosphate with the net production of glyceraldehyde 3-phosphate for the synthesis of sucrose and starch. Three molecules of CO2 are fixed by RuBisCO to produce six molecules of PGA, which will give one molecule of glyceraldehyde 3-phosphate which is a triose phosphate.
- Regeneration: After forming six molecules of 3-phosphoglycerate, six ATPs and six NADPH are used to generate six molecules of glyceraldehyde 3-phosphate. Only one of these molecules of glyceraldehyde 3-phosphate is then used to form fructose 6-phosphate and starch. The other five molecules of glyceraldehyde 3-phosphate are converted in a series of steps to three molecules of ribulose 5-phosphate which are then phosphorylated using three molecules of ATP to form three molecules of ribulose 1,5-bisphosphate, for another cycle. After completion of one cycle, taking three molecules of CO2 as one molecule of glyceraldehyde 3-phosphate, requires 6+3=9 ATPs and 6 NADPHs.
C3 and C4 Pathways
C3 and C4 are photosynthetic pathways present in terrestrial plants. C3 plants use the C3 pathway or Calvin cycle, and C4 plants use the C4 pathway, or Hatch-Slack pathway, for the dark reaction of photosynthesis. Photosynthesis is the process in which different bacteria like cyanobacteria and eukaryotes like green plants, and algae can convert solar energy to chemical energy. In this process, solar energy is absorbed and used to synthesize carbohydrates from carbon dioxide and water.
Table of Content
- What are C3 and C4 Pathways?
- C3 Pathway
- C4 Pathway
- Difference Between C3 and C4 Pathway
- FAQs on C3 And C4 Pathways
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