Nutrient sources involving amino acids are either imported or synthesized de novo and enter one carbon metabolism. One carbon metabolism can be viewed as a set of two modular units (i.e. two pathways existing separately from one another) involing the Folate Cycle and Methionine Cycle. Through these metabolic cycles, nutrients are processed. Upon processing, multiple outputs can be generated including nucleotides, proteins, lipids, reducing power, and substrates for methylation reactions.