As in bacteria, the cytoplasm of eucaryotes is a 20% aqueous protein solution, containing dissolved ions, small molecules, and many enzymes. In eucaryotic cells, cytoplasm also is the suspension medium for the nucleus, mitochondria, and other organelles.

It is a viscous fluid with some degree of structure. Filaments 40 in diameter and 200--diameter microtubules can be seen anchoring various organelles to one another.

Many important chemical reactions take place in the cytoplasm, including glycolysis as far as pyruvate, gluconeogenesis from phosphoenolpyruvate back to glucose, fatty-acid synthesis from acetyl coenzyme A, biosynthesis of the amino acids that the cell can make (this varies from one organism to another), synthesis of porphyrin and other organic molecules, and the priming of tRNA with amino acids for protein synthesis.