Question: where does de novo synthesis of purine occur
[{'answer': 'attached to ribose', 'provenance': [{'wikipedia_id': '5670575', 'title': 'De novo synthesis', 'start_paragraph_id': 4, 'start_character': 206, 'end_paragraph_id': 4, 'end_character': 224, 'bleu_score': 1.0, 'section': 'Section::::Nucleotide.\n'}]}, {'provenance': [{'wikipedia_id': '5670575', 'title': 'De novo synthesis', 'start_paragraph_id': 4, 'start_character': 0, 'end_paragraph_id': 4, 'end_character': 376, 'bleu_score': 0.6941563627394071, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 14319787464817869407}, 'section': 'Section::::Nucleotide.\n'}]}]