Carboxylation is a process of combining a coenzyme with carbon dioxide.Explanation Carboxylation is the chemical reaction where carbon dioxide (CO₂) is added to a molecule, often with the help of a coenzyme, such as biotin.Example: In photosynthesis, carbon dioxide is added to ribulose bisphosphate (RuBP) with the help of the enzyme Rubisco, forming a 6-carbon compound.In metabolism, biotin acts as a coenzyme in carboxylation reactions (like converting pyruvate to oxaloacetate).