Eukaryotic cells have a wide variety of distinct shapes and internal
organizations. Cells are capable of changing their shape, moving organelles, and
in many cases, move from place to place. This requires a network a protein
filaments placed in the cytoplasm known as the cytoskeleton.
The two most important protein filaments are called the actin filaments and
the microtubules. The actin is responsbile for contraction (like in muscles) and
the microtubules are for structural strength.