Centrioles are located within animal cells within the cell’s centrosome, which is an area near the nucleus where the cell’s microtubules are initiated. Centrioles are about 250 nm in diameter and are composed of nine sets of triplet microtubules arranged in a ring. Before a cell divides, centrioles replicate and are therefore involved in cell division. Under an electron microscope, the centrioles appear as long cylinders from the longitude section’s viewpoint, and they appear as hollowed stars from the cross section’s viewpoint.