Free nucleotides must be available in a cells nucleus to produce mrna strands. where do these free nucleotides come from

All four nucleotides (adenine, guanine, thymine, cytosine) are synthesized in the liver. The nucleotides can be synthesized de novo or recycled through salvage pathways. The synthesis occurs in the cytoplasm of the cell, not within a specific organelle. The components which are used for the nucleotide synthesis are derived from biosynthetic precursors of carbohydrate and amino acid metabolism, and from ammonia and CO2.