Cell biologists view the terrain of organelles using dyes and microscopy, while biochemists try to unlock functional clues by smashing up organellar compartments via density gradient centrifugation. Proteomic scientists have further refined the recipe: take organelle-enriched fractions, then sequence peptides with mass spec. It’s been a successful tactic — databases are brimming with cytoplasmic and nuclear organelle data — but it’s not perfect.