At one time, it was believed that the cytoplasm intervening between the discrete organelles and deposits was unstructured. This belief was reinforced by the use of homogenization and centrifugation of the homogenates to yield fractions consisting of recognizable membrane-bound organelles. The final supernatant produced by this process, after the separation of organelles, is called the cytosol. The cytosol constitutes about half the total volume of the cell. Homogenization of cells disrupts a delicate microtrabecular lattice that incorporates filaments of actin, microtubules, intermediate filaments, enzymes, and other soluble constituents into a structured cytosol. The cytosol coordinates the intracellular movements of organelles and provides an explanation for the viscosity of the cytoplasm. Soluble (not membrane-bound) enzymes, such as those of the glycolytic pathway, for example, function more efficiently when organized in a sequence instead of having to rely on random collisions with their substrates. The cytosol provides a framework for this organization. It contains thousands of enzymes that produce building blocks for larger molecules and break down small molecules to liberate energy. All machinery to synthesize proteins (rRNA, mRNA, tRNA, enzymes, and other factors) is contained in the cytosol.
Cell Components & Diseases