Question: how many levels of protein structure are there
[{'answer': 'four', 'provenance': [{'wikipedia_id': '969126', 'title': 'Protein structure', 'start_paragraph_id': 5, 'start_character': 10, 'end_paragraph_id': 5, 'end_character': 14, 'bleu_score': 1.0, 'section': 'Section::::Levels of protein structure.\n'}]}, {'provenance': [{'wikipedia_id': '969126', 'title': 'Protein structure', 'start_paragraph_id': 5, 'start_character': 0, 'end_paragraph_id': 5, 'end_character': 51, 'bleu_score': 0.7598356856515921, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 15651982943496696295}, 'section': 'Section::::Levels of protein structure.\n'}]}, {'provenance': [{'wikipedia_id': '969126', 'title': 'Protein structure', 'section': 'Section::::Levels of protein structure.\n', 'start_paragraph_id': 5, 'end_paragraph_id': 5, 'meta': {'evidence_span': ['There are four distinct levels of protein structure.', 'There are four distinct levels of protein structure.', 'There are four distinct levels of protein structure.']}}]}, {'provenance': [{'wikipedia_id': '50520262', 'title': 'Mosaic protein', 'section': 'Section::::Abstract.', 'start_paragraph_id': 1, 'end_paragraph_id': 1, 'meta': {'evidence_span': ['Proteins are made up of amino acids which connect by peptide bonds and form into polypeptide chains. There are four levels of protein organization: primary structure- the amino acid sequences; secondary structure- different types of folded shapes (ex: alpha helices and beta sheets); tertiary structure- includes all the different folding that happens on one polypeptide chain; quaternary structure- the combination of multiple polypeptide chains. (Note: not all proteins reach this fourth level of organization).', 'There are four levels of protein organization: primary structure- the amino acid sequences; secondary structure- different types of folded shapes (ex: alpha helices and beta sheets); tertiary structure- includes all the different folding that happens on one polypeptide chain; quaternary structure- the combination of multiple polypeptide chains.', 'There are four levels of protein organization: primary structure- the amino acid sequences; secondary structure- different types of folded shapes (ex: alpha helices and beta sheets); tertiary structure- includes all the different folding that happens on one polypeptide chain; quaternary structure- the combination of multiple polypeptide chains.']}}]}]