Centrosomes

Centrosomes are cell organelles that act as the main microtubule-organising centres (MTOCs) in animal cells. Located near the nucleus, they play a key role in cell division by organising the spindle fibres that pull chromosomes apart.

Structurally, a centrosome consists of two centrioles surrounded by pericentriolar material. While centrosomes are well-defined in animal cells, most plant cells lack typical centrosomes but still organise microtubules through similar regions during cell division.

Structure of the Centrosomes

The mother centriole and the daughter centriole, which are perpendicular to one another and connected by interconnecting fibres, make up the centrosome. It is made up of a protein complex that helps in the production of extra microtubules.

• The centrioles are encased in an amorphous pericentriolar matrix.
• Cytoplasmic microtubules are formed and anchored as a result of it.
• Animal cells' centrosomes closely resemble DNA. One centrosome from the parent cell is transmitted to each daughter cell during cell division.
• Centrosome division begins in proliferating cells before the S-phase does. The newly formed centrosomes organise the mitotic spindles.
• The centrosome arranges an astral ray of microtubules during interphase, which helps in intracellular transport, cell adhesion, cell polarity, etc.
• The mother centriole and daughter centriole, which are the mature and immature centrioles, respectively, in post-mitotic cells, make up the centrosome.

Centrosome Cycle

There are four stages in the centrosome cycle:

1. Centrosome duplication takes place at the G1 stage.
2. The centrosome develops during the G2 stage.
3. Where centrosome division takes place during the mitotic phase.
4. Where the chromosomal confusion occurs, late mitotic stage.

Characteristics of the Centrosomes

Characteristics of the centrosomes are given below:

• Centrosomes are cell organelles that serve as the main place for sorting microtubules in animal cells. Two barrel-shaped microtubule clusters, known as "centrioles," and a collection of proteins that help in the shaping of more microtubules are used to create centrosomes.
• Centrosomes are not found in plant cells. Instead, plant cells use other structures to organise their microtubules.
• Centrosomes are usually found close to the nucleus inside animal cells. They act as the cell's organising centre. They help to arrange structures called microtubules during cell division.

Function of the Centrosomes

The major functions of the centrosome are given below:

• Microtubule Organisation: Centrosomes act as the main microtubule-organising centres (MTOCs), helping to organise the microtubule network within the cell.
• Cell Division: They play a crucial role in forming the mitotic spindle during cell division, ensuring proper segregation of chromosomes.
• Chromosome Number Monitoring: Centrosomes help to monitor and maintain the correct chromosome number during cell division.
• Cytoskeletal Arrangement: They control the movement and arrangement of cytoskeletal elements, facilitating changes in cell shape and structure.
• Cell Polarity and Motility: Centrosomes contribute to establishing cell polarity and directing cell movement.
• Intracellular Transport: They help in the intracellular transport of organelles and vesicles by organising microtubules as tracks for motor proteins.

Centrosomes in an Animal Cell

Animal cells include centrosomes. When cells divide, centrioles play a significant role. The centrioles and various centrosome segments are duplicated during the interphase of an animal cell; however, it is unclear how this duplication takes place at this time.

• The two sets of centrioles are initially close together, but as mitosis progresses, the first centrosome separates, and the sets are split apart, resulting in one pair of centrioles being located in each of the new microtubule-sorting centres.
• Asters, star-shaped clusters of microtubules, emerge from these new foci.
• The centrioles help the microtubules form an axle-shaped development that travels the length of the cell as the cilia migrate to constrict the cell shafts.
• The centrosome helps in the formation of the mitotic spindle but does not participate in cell division in the majority of animal cells.
• Due to chromosome instability or the capacity of cancer cells to spread through the body, centrosome malfunction in humans can result in cancer.

Centrosomes in Plant Cells 

Plant cells include centrosomes to organise microtubules. Plants and other growths without centrosomes need MTOC structures. Except for the male gametes, which are completely present in a few blooming plants, plant cells do not include axle post bodies or centrioles (conifers).

• The crucial MTOC abilities for shaft attachment and microtubule nucleation give the impression of being absorbed by the plant cell's nuclear envelope during mitosis.
• Both fungi and plants lack centrosomes. Except for the flagellated male gametes that are exclusively seen in a few flowering plants, plant cells do not have spindle pole bodies or centrioles.
• The nuclear envelope appears to perform the primary role of MTOC for spindle organisation and microtubule nucleation during plant cell mitosis.
• The primary cytoskeletal components that help in the regulated movement are shared by animal and plant cells.

Microtubules Organising Centre

During cell division, the spindle fibres made of microtubules are crucial. It is not a component of every cell because it is not present in plant cells. As the primary microtubule-organising centre (MTOC) in animal cells, the centrosome coordinates interphase cell movement, bonding, and polarity and helps mitotic spindle pole organisation.

Mitosis During Fertilisation

A new cell called a zygote is created during fertilisation when the sperm and egg cells join. Chromosomes from both the sperm and the egg cells are present in the zygote. After conception, the zygote continues to go through cell division, and after a few weeks, it grows into a human embryo, ultimately becoming a baby.

Centrosome Alterations in Cancer Cells

Centrosomes are the major organising centres of microtubules in mammalian cells and form spindle poles during mitosis. In our current ultrastructural analysis of 31 human breast tumours, we found that the centrosomes of most tumours displayed significant alterations compared to those of normal breast tissue. These changes include: 

• Excess centrioles, 
• Excess pericentrosomal material, 
• Disturbance of the centriole barrel structure, 
• Unintegrated microtubule complexes, 
• The centriole, which functions as the ciliary basal body, and 
• Wrong centrosome. 

Centrosomes vs Centrioles

The difference between centrosomes and centrioles is:

Related Articles:

• Anaphase
• Microbodies
• Centriole
• Difference Between Centromere and Kinetochore
• Cell Organelles