In eukaryotic cells, the cytoplasm is the area between the plasma membrane and the nuclear envelope. Since prokaryotic cells lack a nucleus, the cytoplasm refers to everything enclosed within the plasma membrane. In both cell types, the cytoplasmic space is filled up by a gel-like matrix called the cytosol. The cytosol is an aqueous solution that contains many soluble ions, small molecules, and macromolecules. The cytoplasm of eukaryotic cells also includes numerous membrane-bound organelles that perform specialized cellular functions, such as the mitochondria, the endoplasmic reticulum, and the Golgi apparatus. A framework of protein fibers present in the cytoplasm – the cytoskeleton, gives the cell its shape and structure. It also helps in intracellular transport and cell motility. In addition, many non-organelle cellular functions, such as protein synthesis, also take place in the cytoplasm. The aqueous nature of the cytoplasm facilitates protein folding by repelling hydrophobic amino acid side-groups into the protein core. Some cells also store insoluble metabolic products like glycogen in their cytoplasm in the form of inclusions.