Centrosome

Centrosomes are organelles that serve as the main organisational centres of microtubules for animal cells.

Centrosomes are made up of the arrangement of two barrel-shaped clusters of microtubules, called “centrioles”, and a complex of proteins that help form additional microtubules.

These proteins allow centrosomes to initiate and stop the formation of microtubule proteins. This allows them to control the formation of mitotic spindle fibres and other structures that play an important role in cell development.

Centrosomes help with several important functions, including:

• Organising changes in the shape of the cell membrane that allow the membrane to be “pinched” in two during the cell division.
• Ensuring that chromosomes are properly distributed to daughter cells by the creation and shortening of mitotic spindle fibres.
• Monitoring other important changes in cell membrane shape, such as those observed in the phagocytosis.

In animal cells, centrosomes are treated in the same manner as the DNA.

Each cell The daughter cell obtains a centrosome from the mother cell during cell division. The centrosome is then copied during cell cycle so that the cell can give one to each daughter cell when it divides.

During cell division, when chromosomes line up and then push towards opposite ends of the cell, it is the centrosomes that are responsible.

Centrosomes, which migrate to opposite “poles” of the cell as the cell prepares for division, direct the mitotic spindle fibres. These spindle fibres separate the sister chromatids and ensure that one copy of each chromosome ends in each daughter cell.

The following graphic shows a cell in the middle of the telophase of cell division. You can see that your DNA has already been pulled by mitotic spindle fibres to opposite sides of the mother cell, and that the cytoskeleton is now beginning to “pinch” the cell in two.

In the absence of centrosomes, some animal cells can still complete this variety of DNA, but the process is less reliable. Some animal species can develop normally without centrosomes; but in most species, cells can begin to divide incorrectly or stop dividing if centrosomes are destroyed.

Mutations that impair centrosome function are associated with cancer rates in some species, which is consistent with failures in correct DNA sorting. Biologists believe that some cancers are due to errors in chromosome copying and distribution.

Centrosomes are not necessary in plant and fungal cells; because these cells do not change the shape of their cell membranes during cell division. These cells have rigid cell walls and materials that prevent them from changing the shape of their membrane to “pinch” in two during cell division. mitosis.

Function of centrosomes

Centrosomes are sometimes referred to as the “MTOC” or “microtubule-organising centre” of the cell.

They serve to direct the movements of microtubules and other cytoskeletal structures and proteins, ultimately allowing for major changes in the shape of animal cell membranes.

Animal cells are unique among cell types because they are very flexible, giving animals their soft tissues and very versatile bodies. But they also have the ability to have structure and change their shape, allowing movement and many other functions.

When animal cells want to change their shape, protein complexes move cell membranes along a network of microtubules, rigid “skeletal” fibres that can bend and change shape in response to intra- and extracellular signals.

The biggest changes in the shape of a cell’s membrane occur during mitosis, when the entire cell divides in two to form daughter cells.

Mitosis is also when centrosomes play a major role as organisers of the microtubules that separate the sister chromatids, ensuring that each daughter cell gets a full complement of the parent cells’ DNA.

Centrosomes can also orchestrate major changes in cell membrane shape in other circumstances, such as phagocytosis.

This process, which comes from the Greek words for “cell-eating”, occurs when the cell changes shape to completely engulf and “swallow” another cell or element in its environment.

Controversy over the need

For many years, it was believed that animal cells could not divide successfully without centrosomes coordinating sister chromatid separation, changes in the cytoskeleton, and so on. In keeping with this theory, it was observed that some cells in the laboratory stopped dividing altogether, or divided incorrectly, when their centrosomes were destroyed.

But in recent years, it has been discovered that some animal species can develop normally, even if they are genetic mutants that have no centrosomes. Fruit flies and flatworms are among those that achieve successful cell division without centrosomes.

This has raised questions about the actual usefulness of centrosomes and whether the cell can “compensate” for their absence by other mechanisms. Some scientists propose that centrosomes may assist the processes described in this article, but not be vital to them.

More data are needed before scientists can say with certainty whether centrosomes are essential for cell division and what they can do that cells don’t have other ways to accomplish. But in the meantime, it’s better to assume they are important than not!

• Cell cycle: The cycle by which cells grow from being one newborn “daughter” cell to dividing into two, becoming the “parents” of two “daughter” cells of their own.
• Microtubules: microscopic tubular proteins that form the “cytoskeleton”, the “cytoskeleton”, the skeleton rigid, but dynamic and changing. of a animal cell.
• Mitosis: process by which cells divide in two and produce two daughter cells.