Centriole – Structure & Functions

Centriole is a cell organelle found in animals and some lower plants like Chlamydomonas. It plays a crucial role in several cellular processes, including cell division regulation and cytoskeletal organization. Centriole structure is constituted by a protein known as tubulin.

Centrioles produce spindle fibers that bond to the centromeres of chromosomes, facilitating the separation of sister chromatids to opposite cell poles during the anaphase stage of mitosis. This article discusses the definition of centrioles, their structure, the functions of centrioles in animal cells, and centriole replication.

Centriole Definition

Centrioles are cylindrical or barrel-shaped cell organelles that help animal cells copy themselves. Centriole also plays a vital role in the cell cycle and other cell developmental processes.

What is Centriole?

Centrioles are cylindrical or barrel-shaped cell organelles that have essential roles in the formation of centrosomes, cilia, and flagella. A Belgian embryologist, Edouard van Beneden, discovered centrioles in the late 19th century. He was studying the eggs of marine invertebrates when he observed these structures.

In animal cells, centrioles are usually present in pairs; this pair is located within a centrosome. Within the centrosome, the centrioles are angled perpendicular to each other. The cells undergo division via mitosis where the centrioles form areas that are responsible for the formation of mitotic spindle.

Diagram of Centriole

The labelled diagram of centriole is given below:

Centriole Structure

Centrioles are composed of nine sets of triplet microtubules. These microtubules are arranged in a circle, with each triplet consisting of three microtubules. These triplet microtubules are connected via connecting fibres. These fibres help maintain the structural integrity and stability of the centriole. Additionally, these connecting fibres provide support and maintain the cylindrical shape of the centriole.

However, some organisms are exceptions to this conformation, for example, the embryos of Drosophila melanogaster and C. elegans. In Drosophila melanogaster, nine pairs of microtubules form instead of triplets, while the early embryos and sperm cells of C. elegans contain nine individual microtubules.

Centrioles Function

Centrioles play essential roles in various cellular processes. Some of the main functions of centrioles include:

• Centrioles aid in microtubule formation, vital for the cytoskeleton. Microtubules maintain cell shape and support intracellular transport.
• Centrioles play a crucial role in forming cilia and flagella. Cilia are short, hair-like structures on the cell surface, while flagella are longer, whip-like extensions.
• Centrioles assist in spindle fiber formation for cell division, separating chromosomes into daughter cells.
• In cells with cilia or flagella, centrioles serve as basal bodies, anchoring and supporting the growth of these structures.
• The centrosome, containing centrioles, organizes cellular components by developing microtubules, crucial for intracellular transport and positioning.

Centriole Replication

Centriole replication occurs in S-phase of cell division and helps in the formation of the mitotic spindle fibres. These fibres are an essential component of cell division as they help in the segregation of chromosomes. The steps involved in centriole replication are:

1. Inititation: In the S phase of the cell cycle, DNA replication occurs. The duplication of the centriole is coordinated with DNA replication to make sure cell division occurs properly.
2. Duplication: In this phase, the centriole duplicates to form a new centriole adjacent to it. This results in the centrosome, which contains two centrioles.
3. Elongation: Certain proteins help in the assembly of centrioles, and the polymerization of tublin helps in the formation of microtubules. The centrioles elongate, resulting in a cylindrical shape.
4. Maturation: As the centrioles mature, they become capable of acting as MTOCs (Microtubule Organizing Centers).
5. Cell division: After maturation, the centrioles help in the proper arrangement of the mitotic spindle apparatus, thus enabling proper chromosome segregation during mitosis and meiosis. During cell division, centrioles in animal cells move to the opposite pole and help in the formation of spindles.
6. Regulation: This whole process of centriole replication is governed by certain checkpoints in the cell cycle and various regulatory proteins. Any disruption in centriole replication can lead to genomic instability, thus resulting in diseases like cancer.

Conclusion: Centriole

The centriole is a specialized organelle in animal cells and certain lower plants. Centriole plays a crucial role in numerous cellular processes. They aid in the formation of the centrosome and contribute significantly to cell division. Additionally, centrioles are instrumental in constructing cilia and flagella, facilitating cellular movement and sensory functions. Their involvement extends to maintaining the cytoskeleton, ensuring cellular organization, and orchestrating intracellular transport. Fundamentally, centrioles are essential for cellular structure, function, and organization.

FAQs – Centriole

What is a pair of centrioles called?

A pair of centrioles is known as a diplosome. This paired structure of centrioles is found within the centrosome.

How many centrioles are there in a cell?

The number of centrioles in a cell varies depending on the type of cell and the stage of the cell cycle but typically an animal cell contains two centrioles.

What is the difference between a centriole and a centrosome?

Centrioles are cylindrical structures that are formed of microtubules, these microtubules act as the foundation for centrosomes. The centrosome is a more complex structure that is constituted by two centrioles enveloped by a protein-rich matrix.

What is a centriole made of?

A Centrioles is made up of microtubule triplets and the microtubules are composed of a polymerized globular protein called tubulin.

What are the two main functions of centrioles?

The two main functions centrioles perform include cell division and ciliogenesis. In cell division, centrioles help in the formation of spindle fibers while in ciliogenesis, centrioles help in the formation of cilia and flagella.

During which phase of mitosis do centrioles replicate?

The centrioles replicate during the first stage of mitosis known as interphase. This stage occurs just before cell division, which marks the start of mitosis and meiosis in cell cycle.