In this section we will discuss the intracellular components that are not organelles. The cytoskeleton
and cytosol are structural elements that help provide the cell with its structure. The cytoskeleton is
composed of protein filaments and is found throughout the inside of a eukaryotic cell. The cytosol is
the main component of the cytoplasm, the fluid that fills the inside of the cell. The cytoplasm is
everything in the cell except for the cytoskeleton and membrane-bound organelles. Both structures,
the cytoskeleton and cytosol, are "filler" structures that do not contain essential biological molecules
but perform structural functions within a cell.
The interior of a cell is composed of organelles, the cytoskeleton, and the cytosol. The cytosol often
comprises more than 50% of a cell's volume. Beyond providing structural support, the cytosol is the
site wherein protein synthesis takes place, and the provides a home for the centrosomes and
centrioles. These organelles will be discussed more with the cytoskeleton.
Figure %: Location of the cytosol within a cell.
The cytoskeleton is similar to the lipid bilayer in that it helps provide the interior structure of the cell
the way the lipid bilayer provides the structure of the cell membrane. The cytoskeleton also allows
the cell to adapt. Often, a cell will reorganize its intracellular components, leading to a change in its shape. The cytoskeleton is responsible for mediating these changes. By providing "tracks" with its
protein filaments, the cytoskeleton allows organelles to move around within the cell. In addition to
facilitating intracellular organelle movement, by moving itself the cytoskeleton can move the entire
cells in multi-cellular organisms. In this way, the cytoskeleton is involved in intercellular
The cytoskeleton is composed of three different types of protein filaments: actin, microtubules, and
Actin is the main