Centrioles: Definition, Structure, Function, Parts, Roles

Centrioles are cylindrical organelles made up of a protein called tubulin.

Tiny construction specialists are indispensable for the processes of cell division and construction.

What is Centriole?

Centrioles are cylindrical organelles of eukaryotic cells which are made of microtubule triplets of a particular kind. It has a critical function in cell division, where they position microtubules to create the spindle fibres during mitosis and meiosis; this is to guarantee the proper distribution of chromosomes. In the same measure, they anchor sites for ciliation and fractionation, which are crucial for cell locomotion and instinctual apparatuses like cilia and flagella.

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Centrioles are usually double, provided they are in the centrosome area which is close to the nucleus of the cell. Like replication, their reproduction is very controlled, having clear and strict structures that are fundamentally important for cell health and functionality in different species and at different stages of development.

Centrioles Structure

The structure of centrioles is discussed below:

Basic Structure

Centrioles are cylindrical structures usually ranging in diameter to about 200 nm and in length to 500 nm in the human cell.

Each centriole is made of nine triplets of microtubules disposed of in a circle, thus it represents a barrel shape.

Diagram of Centriole Structure

Ultrastructure

Centrioles are comprised of microtubule triplets; each of the triplets has a complete microtubule known as the Atubule and two demarcated microtubules, the Btubule and the Ctubule.

Tubulin proteins are the main chromosome of centrioles; however, certain proteins like pericentrin and centrin are involved in the stability of centrioles.

Diagram showing detailed microtubule arrangement

Centrioles Function

The functions of centrioles are discussed below:

Role in Cell Division

One of centrioles' main functions is in the formation of spindle fibres, which is instrumental in the separation of chromosomes during the division period.

In mitosis and meiosis, centrioles play a significant role in assembling the spindle apparatus thereby affecting proper orientation and segregation of chromosomes as well as cell division.

Formation of Cilia and Flagella

Centrioles act as basal bodies to help in the process of growth of cilia and flagella which are important in the movement and sensory organelles of the cell.

Organisation of the Mitotic Spindle

Centriole replication is semiconservative in which each new pair of centrioles consists of one old, or mother, centriole, and one new, or daughter, centriole.

Diagram of centrosome organisation during cell division

Centriole Duplication and Cycle

The centrosome duplication is discussed below:

Duplication Process

Replication starts in the S phase of the cell cycle for new centrioles to start forming alongside older ones.

Phases:

In the G2 phase, the new centrioles begin to grow and reach maturation during this phase. In the Mphase, a centriole pair gets separated so that each of the two daughter cells gets a centrosome.

Diagram of centriole duplication cycle

Regulation of Duplication

Proteins, including SAS6 and STIL, are important in the start and correct development of new centrioles in the course of duplication.

The centrosome cycle is tightly controlled and accurately coordinated with the cell cycle for achieving accurate centriole duplication and transportation, which is very important for genome stability as well as the efficient functioning of the cell.

Centrioles and Centrosomes

Centrioles and Centrosomes are discussed below-

Definition of Centrosome

The centrosome is a small organelle located in the cytoplasm and consists of two centrioles surrounded by a granule material called pericentriolar material (PCM). Serving as the primary focusing centre of the microtubules in the cell, it is primarily responsible for the arrangement of microtubules and their segregation during cell division.

Diagram of centrosome with centrioles

Relationship Between Centrioles and Centrosomes

Centrioles are part of centrosomes and play a crucial role in centrosome duplication.

Role in microtubule organisation

Centrioles are also involved in the organisation of microtubules in the centrosome contributing to the formation of mitotic spindle during cell division and structural framework of the cell.

Abnormalities and Diseases Related to Centrioles

The abnormalities are discussed below:

Centriole Defects

Damage to centrioles causes improper cell division and aneuploidy or genomic instability, which are related to different diseases. Also, centriole ultrastructure alterations may influence cilia development and the latter’s performance, which results in numerous cellular abnormalities.

Defects are associated with several diseases such as microcephaly, which is a result of reduced brain size by improper cell division, and different types of cancer which involve abnormal cell division and instability of the genome.

Centrosome Amplification

Centrosome duplication in which at least one cell has more than two centrosomes can cause multipolar mitoses that in turn cause chromosome segregation disorders causing aneuploidy. This condition is frequently detected in cancer cells and is linked with the advancement of the disease and worse outcomes.

Diagram showing abnormal centrosome amplification

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