The pyrimidine ring system is shown below.What is the source of the N-3 during the de novo biosynthesis of pyrimidines? 
Definitions:
Ritalin
is a medication primarily used to treat Attention Deficit Hyperactivity Disorder (ADHD) by stimulating the central nervous system.
Child Psychopathology
The study of mental disorders and behavioral problems in children and adolescents.
Anna Freud
A psychoanalyst known for her work with children and contributions to ego psychology.
Melanie Klein
A psychoanalyst known for her work in child psychology and psychoanalytic theory, particularly for her theories on object relations.
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