Centriole

Tiny parts live inside your cells.

These parts are shaped like small tubes. They are found in most living things. Some plants do not have them.

These tubes help the cell divide. They help make tiny tails for movement. These tails help sperm swim.

One part is called the mother. A new daughter part grows next to it. This helps the cell make more parts.

These little parts are very busy! They help your body work well.

Inside most cells, there are tiny parts shaped like tubes. We call these parts centrioles.

They are made of a protein called tubulin. Most centrioles are made of nine sets of small tubes. These small tubes are called microtubules.

Centrioles help the cell in many ways. They help the cell divide into two new cells. They also help make cilia and flagella. These are tiny tails that help cells move.

In sperm, these tails help the cell swim.

Centrioles can also make copies of themselves. A cell usually has two centrioles. One is an older mother centriole. The other is a younger daughter centriole. During cell division, a new centriole grows on each one. This way, the cell makes more parts for the new cells.

Most living things have centrioles. However, some plants like flowering plants do not have them. Some tiny animals like fruit flies also have different types of centrioles. These parts are very important for how life works.

Inside many living cells, there are tiny, tube-shaped parts called centrioles.

They are mostly made of a protein called tubulin. Most centrioles are found in a pair within a structure called a centrosome. This centrosome is surrounded by a dense mass of material called the pericentriolar material, or PCM. Centrioles are very important for organizing the inside of a cell. They help decide where the nucleus sits in the cell. They also help arrange the cell's shape and layout.

Centrioles work in a very specific way to help cells grow and move. Most centrioles are built from nine sets of microtubule triplets. These triplets are small tubes arranged in a cylinder shape. Some living things have slightly different patterns. For example, fruit flies have nine doublets instead of triplets. The tiny worm C. elegans has nine single tubes. During cell division, centrioles can make copies of themselves. A cell starts with an older mother centriole and a younger daughter centriole. A new centriole grows at the end of both existing ones.

Scientists have been studying these tiny parts for a long time. Walther Flemming and Edouard Van Beneden discovered the centrosome in 1875 and 1876. In 1883, Van Beneden saw that centrosomes were made of two centrioles at a right angle. Theodor Boveri later gave us the name "centrosome" in 1888. He also named the "centriole" in 1895. Another scientist, Theodor Wilhelm Engelmann, named the basal body in 1880. Later, in 1950, Étienne de Harven and Joseph G. Gall figured out how centrioles duplicate.

Centrioles perform many vital jobs for different living things. They help create cilia and flagella, which are tiny hairs or tails. These tails allow cells to move through their environment. In sperm cells, centrioles help form the tail that lets them swim. They also help a new embryo grow after fertilization. If centrioles do not work right, it can lead to diseases like Meckel-Gruber syndrome.

Not every living thing has them, though. Flowering plants and conifers do not have centrioles at all. Most fungi also lack these tiny structures.

You can think of centrioles as the tiny construction managers of the cell. Just as a manager helps organize a building site, centrioles organize the cell's parts. They make sure everything is in the right place before a cell divides. Without them, the cell might not know how to split into two healthy parts. Even though they are too small to see without special tools, they run the show. They are a key reason why many living things can grow and move.

A centriole is a cylindrical organelle found within most eukaryotic cells. It is primarily composed of a protein called tubulin. These tiny structures are essential for organizing the internal layout of a cell. They play a critical role in determining the position of the nucleus. Centrioles also help manage the spatial arrangement of the cell's components.

Centrioles usually exist in pairs within a larger structure called a centrosome. This centrosome is surrounded by a dense, highly ordered mass of material known as the pericentriolar material, or PCM. The two centrioles in a centrosome are typically attached to one another at a right angle, which is called an orthogonal arrangement. This organized structure helps the cell manage its internal environment and prepare for division.

Most centrioles follow a specific structural pattern. They are built from nine sets of microtubule triplets arranged in a cylinder. However, there are notable deviations from this standard design in nature. For example, the fruit fly *Drosophila melanogaster* has nine microtubule doublets. The tiny worm *Caenorhabditis elegans* uses nine singlets in its sperm cells and early embryos.

Centrioles undergo a specific process of self-replication during the cell cycle. Before DNA replication begins, a cell contains one older mother centriole and one younger daughter centriole. During cell division, a new centriole grows at the proximal end of both existing centrioles. After this duplication, the two new pairs remain attached orthogonally until mitosis occurs. At that point, an enzyme called separase helps the mother and daughter centrioles separate.

Our understanding of these structures grew through many scientific discoveries. Walther Flemming and Edouard Van Beneden jointly discovered the centrosome in 1875 and 1876. In 1883, Van Beneden observed that centrosomes consisted of two orthogonal centrioles. Theodor Boveri later introduced the term "centrosome" in 1888 and the term "centriole" in 1895. Additionally, Theodor Wilhelm Engelmann named the basal body in 1880. Finally, Étienne de Harven and Joseph G. Gall independently worked out the pattern of centriole duplication around 1950.

The functions of centrioles are vital for reproduction and movement. During interphase, they are responsible for producing cilia, which are hair-like structures on cells. In sperm cells, centrioles are necessary to form the flagellum, or the tail that allows for movement. The sperm also provides the centriole required to create the centrosome and microtubule system in a new zygote.

Errors in centriole function can lead to serious biological consequences. If cells cannot use centrioles to build functional flagella or cilia, it can cause genetic diseases. Specifically, the inability of centrioles to migrate properly before ciliary assembly is linked to Meckel–Gruber syndrome. While some experiments show cells can survive without centrioles via a process called *de novo* synthesis, mutant flies lacking them die shortly after birth because they lack cilia.

Centrioles are not universal to all life. They are absent in conifers, flowering plants, and most fungi. They only appear in the male gametes of specific groups like bryophytes and certain seedless vascular plants. This suggests that the last common ancestor of all eukaryotes, known as LECA, was a ciliated cell with centrioles. This evolutionary history shows how these small organelles have shaped the diversity of life on Earth.