College

Which compound is produced during carbon fixation?

A. PGA
B. G3P
C. RuBP
D. C6H12O6

Answer :

In the process of photosynthesis, carbon fixation is a crucial step where inorganic carbon dioxide (CO₂) is converted into organic compounds. This takes place in the Calvin cycle, also known as the light-independent reactions or the dark reactions.

During carbon fixation, carbon dioxide is incorporated into an organic molecule. Here’s a step-by-step outline of the process:

1. Carbon Fixation Begins: CO₂ is combined with a 5-carbon sugar named ribulose bisphosphate (RuBP). This reaction is catalyzed by an enzyme called ribulose bisphosphate carboxylase/oxygenase, commonly known as RuBisCO.

2. Formation of an Unstable 6-Carbon Intermediate: The combination of CO₂ and RuBP quickly forms a very unstable 6-carbon compound. Due to its instability, this compound breaks down almost immediately.

3. Production of 3-Phosphoglycerate (PGA): The unstable 6-carbon compound splits into two 3-carbon molecules. These molecules are known as 3-phosphoglycerate (PGA).

Therefore, during the process of carbon fixation in the Calvin cycle, the first stable compound that is produced is 3-phosphoglycerate (PGA).