A centriole is a specialized organelle, also called a cell body, that is found in the cells of most animals. It is roughly tubular in shape and plays an important role in cell division. These cell structures are so tiny that their details cannot be seen without the assistance of an electron microscope; during cell division, their activity can clearly be seen under magnification.
There are many organelles, including centrioles, that help a eukaryotic cell to run smoothly. A eukaryotic cell is a complex cell with a number of tiny organs that all serve different functions. It also has a cell nucleus and a complex physical structure that sets it aside from prokaryotic cells, like those of bacteria. Humans, among other animals, are made from eukaryotic cells, and these cells periodically divide to renew themselves so that their larger hosts can grow and remain healthy.
In animals that have centrioles, each cell has a pair. Their shape is actually quite fascinating and beautiful; they consist of nine triplets of microtubules arranged in a pinwheel shape around a central cylinder. The two collectively make up a structure in the cell which is called the centrosome, with one centriole aligned in an orientation that is perpendicular to the other. This organelle is at the core of cell division.
When a cell divides, the centrosome replicates itself, and the two move to opposite ends of the cell. Each then sends out spindles, which are supposed to separate the cell's DNA, differentiating a cell into two copies of itself that can then split into fresh cells. An error during this process can create a mutated cell, which may harmlessly die off or become more malignant, depending on the mutation.
The existence of the centrosome was discovered by Theodor Boveri in 1888, and Boveri also put forward an early theory that cancer was caused by errors during cell division. Although mocked at the time, he was later proved correct. In addition to playing an important role in cell division, a centriole also helps to provide structural support for its parent cell. It would also appear that this organelle has its own unique genetic code that is distinct from the code of the cell; scientists believe that this code allows the centrosome to divide and carry out its various functions in the cell.