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Centrosomes

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An organelle is a specialized subunit with a particular function that is typically found within a cell in cell biology. The name organelle is diminutive because it refers to the idea that these structures are components of cells, much like organs are to the body. Organelles are either spatially discrete functional entities without a surrounding lipid bilayer or they are individually encased within their own lipid bilayers (also known as membrane-bound organelles) (non-membrane bound organelles). Although most organelles are functional components of cells, some functional components that extend outside of cells—such as cilia, the flagellum and archaellum, and the trichocyst—are frequently referred to as organelles.

Centrosomes

Centrosomes are organelles that serve as the main hubs for sorting microtubules in animal cells. Two barrel-shaped microtubule clusters, known as “centrioles,” and a collection of proteins that aid in the shaping of more microtubules are used to create centrosomes.

Structure of Centrosomes

The mother centriole and the daughter centriole, which are perpendicular to one another and connected by interconnecting fibers, make up the centrosome. It is made up of a protein complex that aids 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 recently formed centrosomes organize the mitotic spindles. The centrosome arranges an astral ray of microtubules during interphase, which aids 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

 

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.

Centrosomes in 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 centers. 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 Astros migrate to constrict the cell shafts. The organization of the chromosomes as they separate later on during cell division is helped by these shaft strands. The centrosome aids 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. However, there isn’t any solid proof to support this.

Centrosomes in Plant Cells 

Plant cells include centrosomes In order to organize 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 off the impression of being absorbed by the plant cell’s atomic 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 organization and microtubule nucleation during plant cell mitosis.

The primary cytoskeletal components that aid in the regulated movement are shared by animal and plant cells. Plants lack organelle-like centrosomes, but they can generate spindles and have cytoskeletal arrays including the preprophase band, cortical arrays, and phragmoplast that are involved in the basic growth processes.

Centrosome-Microtubules Organizing Centre

During cell division, the spindle fibers made of microtubules are crucial. It is not a component of every cell because they are not present in plant cells. As the primary microtubule-organizing center (MTOC) in animal cells, the centrosome coordinates interphase cell movement, bonding, and polarity and aids mitotic spindle pole organization.

Centrosome- Mitosis during Fertilization

A new cell called a zygote is created during fertilization 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 organizing centers of microtubules in mammalian cells and form spindle poles during mitosis. Centrosome defects have been implicated in disease and tumor progression and are associated with defects in the p53 tumor suppressor gene. In our current ultrastructural analysis of 31 human breast tumors, we found that the centrosomes of most tumors displayed significant alterations compared to those of normal breast tissue. These changes include: 

  1. Excess centrioles, 
  2. Excess pericentrosomal material, 
  3. Disturbance of the centriole barrel structure, 
  4. Unintegrated microtubule complexes, 
  5. Centrosomes of abnormal length, 
  6. The centriole, which functions as the ciliary basal body, and 
  7. Wrong centrosome. 

These changes are associated with altered cell polarity, altered cell and tissue differentiation, and chromosome missegregation due to multipolar mitosis. Importantly, the presence of excess pericentrosomal material was associated with the highest frequency of abnormal mitosis. Centrosome abnormalities can confer a mutator phenotype on tumors, and occasionally cells with a selective advantage emerge and proliferate, driving the tumor into a more aggressive state.

Function 

  1. When a cell divides, the centrosomes assist.
  2. They keep track of the chromosomal count as the cell divides.
  3. Phagocytosis, also promote changes in the cell membrane’s structure.
  4. It aids in the organization of the microtubules during mitosis, ensuring that the centrosomes are dispersed among all of the daughter cells.
  5. They control the movement of cytoskeletal elements and microtubules, enabling adjustments to the animal cell membrane’s shape.

FAQs on Centrosome

Question 1: What are the functions of Spindle Filaments?

Answer:

The variety of different uses of the axle strand finishes attests to the finesse and complexity of the mitotic process. Although it resembles a “back-and-forth,” it must be extremely well-organized in order to ensure that division “passes through” the precise center of each chromosome pair and that every female cell receives precisely one chromosome from each pair.

Question 2: What are the phases of the centrosome cycle?

Answer:

There are four stages in the centrosome cycle:

  • Centrosome duplication occurs during the G1 phase.
  • Centrosome maturation occurs during the G2 phase.
  • The centrosome separates during the division phase.
  • A late mitotic phase during which chromosomal misalignment occurs.

Question 3: What occurs if a cell lacks centrosomes?

Answer:

Centrosomes don’t play a significant role in plants and fungi, but they do in humans because they facilitate cell division. In some extremely unusual situations, chromosomes might perform the duties of centrosomes. People who lack centrosomes may also experience some physical and psychological issues.

Question 4: What is the anatomy of centrosomes?

Answer:

The mother centriole and the daughter centriole, which are perpendicular to one another and connected by interconnecting fibers, make up the centrosome. Its proteins assist cells in performing as they should.

Question 5: What is the role of the centrosome in cell division?

Answer:

Cell science urgently needs to study cell division. Centrosomes play a crucial part in this process. Remember that a solitary centrosome has two centrioles, which are positioned right edges to one another, indicating that the microtubules in these centrioles would be displayed in one of two frequently opposed headings. Review that the two centrosomes of a cell that are now not yet separating are located on the outermost margins of the interphase cell.

This geometry has the effect that as the axle strands of mitosis begin to form, they spread or “fan” outward in the range of bearings from each centrosome itself as well as outward from each side (or “post”) of the cell toward its interior, where cell division is finally clearly visible. Try holding your hands together and clenching with your fingers spread out toward one another as you progressively open your hands. This will give you a general idea of what happens at the centrosomes as mitosis progresses.

Question 6: How is a centrosome different from a centromere?

Answer:

The organelle that houses two centrioles is called the centrosome. In contrast, the centromere is a tightly packed area of the chromosome. In contrast to the centromere, which keeps the sister chromatids of a replicated chromosome together, a centrosome is a microtubule-organizing center.



Last Updated : 12 Jan, 2024
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