{"knowledge_schema": {"broad_category": "Biochemistry \u2192 Protein Analysis \u2192 Mass Spectrometry", "refinement": "This problem involves understanding the effects of post-translational modifications, specifically phosphorylation, on the mass-to-charge ratio (m/z) of peptides during mass spectrometry analysis.", "specific_scope": "The focus is on identifying the correct m/z value that corresponds to the phosphorylated form of the peptide AVDLTKSIR, taking into account the addition of a phosphate group to the serine residue.", "goal": "Determine which m/z value indicates the presence of a phosphorylated serine in the peptide sequence."}, "summary": "This problem relates to biochemistry and mass spectrometry, specifically the analysis of protein modifications. The phosphorylation of serine in the peptide AVDLTKSIR alters its mass, and the task is to identify the m/z value that reflects this modification. The correct answer, 518.271, indicates the mass of the phosphorylated peptide, which includes the additional mass of the phosphate group."}