Centrosome: Overview, Structure, Functions, Diagram
The centrosome is an organelle found in animal cells that functions as the cell's microtubule-organising centre. It also helps to regulate the cell cycle. A centrosome consists of two centrioles. Centrosome is a topic of the chapter Cell: The Unit of Life in Biology.
What are Centrosomes?
The centrosome is the structure of the cell that was most accurately identified with the help of these markers. The microtubule organising centre also called the centrosome, is one of the most important structures in the cell; it is responsible for cell shape control, and microtubule orientation to form a proper network and accurate cell division.
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It is made up of two centrioles enclosed by a matrix of proteins; the centrosome plays the role of making sure that the chromosomes split properly during mitosis. First identified in the 1800s by Theodor Boveri and Edouard van Beneden, the role of the centrosome in organising the cell and dividing it continues to be seen as crucial to cell biology.
Structure of Centrosomes
The structure of centrosomes is given below:
Centriole Pair
Detailed structure:
A typical centrosome houses two centrioles which are cylindrical structures that have nine microtubule triplets within a cartwheellike formation. These triplets produce a frame for the formation of microtubules and are involved in the process of ciliogenesis and flagellogenesis.
Pericentriolar Material (PCM)
Composition and role:
Around the centrioles, there exists pericentriolar material which is a dense proteinaceous material containing among other components gamma-tubulin, pericentrin, and others. PCM is involved in the nucleation and the anchoring of microtubules since it offers the correct conditions for microtubule elongation.
Centrosome Matrix
Around the centrioles, there exists pericentriolar material which is a dense proteinaceous material containing among other components gamma-tubulin, pericentrin, and others. PCM is involved in the nucleation and the anchoring of microtubules since it offers the correct conditions for microtubule elongation.
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Functions of Centrosomes
The functions of centrosomes are discussed below:
Microtubule Organization
One of the significant components of the PCM is the centrosome matrix from which the cell’s MTOC is derived. It controls the formation and addition of microtubules and maintains the cell integrity, vehicular transport, and sometimes the mitotic spindle of the cells.
Microtubule Nucleation and Anchoring:
The Centrosome is the main MTOC of animal cells organizing the network of microtubules that gives structural support and also plays a role in the transport of particles.
Cell Division
Role in mitosis and meiosis:
Not only that, it initiates the formation of new microtubules, besides organizing and strengthening them in the cell. Similarly, the centrosome also duplicates and sets as the poles of the mitotic spindle that are scattered throughout the chromatids accurately.
Formation of the mitotic spindle:
It also directs the formation of the mitotic spindle: this is a structure that is composed of microtubes and is instrumental in the separation of chromosomes to the daughter cells in mitosis and meiosis.
Cell Cycle Regulation
Centrosome cycle and its coordination with the cell cycle:
Centrosome cycling, which includes duplication and maturation, is well-regulated with another cell cycle so that each daughter cell contains one centrosome to retain the order and functionality of a cell.
Intracellular Transport
Role in the trafficking of vesicles and organelles:
The centrosome helps in the transport of vesicles and organelles within a cell by aligning the tracks formed by microtubules, where molecular motors transport the structures to their required destinations with the help of the tracks, thus assisting in intracellular transport.
Centrosome Cycle
The centrosome cycle is discussed below:
Duplication
Centrosome replication takes place at the beginning of the S phase and results in the duplication of the centrosomes to two by the time the cell begins to divide. This process is controlled strictly by the proteins involved in the cell cycle like cyclins and cyclin-dependent kinases to avoid the mistakes that can cause abnormal cell division and aneuploidy.
Separation
In prophase, the centrosomes that have reproduced start to migrate and position themselves at the poles of the cell. This is spearheaded by motor proteins like the dynein and the kinesin that run along the microtubules. By the end of metaphase, the centrosomes ensure that they are located at the spindle poles where they aid in the formation of the mitotic spindle that enables the segregation of chromosomes.
Function in Cytokinesis
The centrosomes need to be positioned correctly and to function in cytokinesis in which the cells are divided into halves by the breakup of the cytoplasm to create two daughter cells. They assist in the organization of the contractile ring and the cleavage furrow that is required for the proper separation of daughter cells thereby increasing the chances of cell division success.
Centrosomes in Different Organisms
The following describes the centrosome in different organisms:
Animal Cells
The animal cell centrosomes are generally present and include two centrioles surrounded by pericentriolar material (PCM). It is the main microtubule organizing center also known as centrosome and plays a significant role in cell division and organization. It can also manifest itself in different types of cells and at different stages of its development as a result of functional needs.
Plant Cells
Unlike animal cells, plant cells do not contain centrosomes and unipolar spindles of plant cells extend from each pole during cell division. Nonetheless, it involves other microtubule organizing centre (MTOCs) scattered all over the cell. They are centrosomes which are analogous to MTOCs and they help in the organization of microtubules as well as proper cell division The nuclear surface is usually a site of microtubule nucleation during mitosis.
Yeast and Other Eukaryotes
Thus, based on the described characteristics, it is found that yeast cells do not contain centrosomes, whereas their MTOCs are known as the spindle pole bodies (SPBs). Thus, in other eukaryotes, different centrosomes or structurally and functionally similar organelles may be present depending on the organism’s necessities. Such adaptations show how different species provide different solutions to the problems of assembling microtubules and dividing the cell.
Centrosome Related Diseases and Disorders
The disorders are discussed below:
Cancer
Centrosome hyperplasia, the state in which cells contain more than two centrosomes, is manifested in cancer very frequently. It can cause defects in spindle formation, chromosome segregation, and antisepsis which are responsible for tumorigenesis and cancer development.
Microcephaly
The improper regulation of some genes that are involved in centrosome duplication and function also hit human beings leading to microcephaly, a situation where an individual has a small brain. These mutations interfere with cell division and the development of the brain which in turn results in serious neurological complications.
Other Disorders
Abnormality of the centrosome can also underlie other diseases including ciliopathies as well. Centrosomes are involved in the formation and function of cilia and if this structure is affected through defects in proteins associated with the centrosome the functions of cilia are affected leading to diseases like polycystic kidney disease, respiratory diseases, and retinal degeneration.
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Frequently Asked Questions (FAQs)
The centrosome in a cell is mostly involved with the manipulation of microtubules and the management of a cell cycle. It is the principal structure required for nucleation of microtubules necessary in the maintenance of cell form, movement of organelles and objects within the cell, and information of the spindle during mitosis.
Centrosomes play an important role in prokaryotic and eukaryotic cell division since the microtubules are used during mitosis and meiosis anchored by the centrosomes. They initiate and orchestrate the formation of the mitotic spindle which is important in the correct division of chromosomes into the newly formed daughter cell.
The main structures that form a centrosome include two centrioles; they are cylindrical structures that consist of microtubule triplets. Around the centrioles, there is the pericentriolar material or PCM, which is a proteinaceous matrix dense composed of various proteins attached to microtubules and involved in the control of its polymerization and depolymerization.
Centrosome replication happens during the cell division cycle in association with longitudinal DNA synthesis in the S phase. Centrosome also duplicates and the two centrosomes are pulled apart and move to the proximal poles of the cell during mitosis. This process is very strictly controlled to achieve the correct course of the formation and operation of the mitotic spindle.
Some of the diseases related to centrosomes include cancer; for instance, centrosome amplification is evident in cell lines and is associated with chromosome instability and tumor progression. Other associated genes include microcephaly, which is also associated with mutations that affect centrosome function in the formation of the brain; and ciliopathies which are characteristic of mutation that affects the ciliary function in the development of the brain.
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