What Happens During Mitosis and How Is It Controlled?

Mitosis is an important part of the cell cycle. It helps living things grow, develop, and fix themselves. During mitosis, one cell divides to create two new cells that are identical to the first one. Let's take a closer look at what happens during this process and how the division is carefully controlled.

The Steps of Mitosis

Mitosis happens in a series of stages:

1. Prophase:

   • The DNA in the cell becomes thicker and forms visible structures called chromosomes.
   • Each chromosome has two parts called sister chromatids that are connected in the middle.
   • The protective layer around the nucleus starts to break down, and a structure called the spindle apparatus begins to form.

2. Metaphase:

   • The chromosomes line up in the middle of the cell.
   • Tiny fibers, called spindle fibers, attach to the center of each chromosome to keep them lined up.

3. Anaphase:

   • The sister chromatids are pulled apart by the spindle fibers, moving toward opposite sides of the cell.
   • This ensures that each new cell will get the same set of chromosomes.

4. Telophase:

   • The now-separated sister chromatids reach the ends of the cell, and new protective layers form around each set of chromosomes.
   • The chromosomes start to turn back into a less visible form called chromatin, and the cell gets ready to divide.

5. Cytokinesis (not technically part of mitosis):

   • This is when the rest of the cell, called the cytoplasm, divides, creating two separate daughter cells.
   • In animal cells, a pinch forms to divide the cells, while in plant cells, a new wall forms between them.

How Mitosis Is Controlled

Mitosis is carefully controlled so cells only divide when they should. Here are some important ways this control happens:

• Cell Cycle Checkpoints:

  • There are specific points in the cell cycle (G1, G2, and M checkpoints) where the cell checks if everything is ready for division.
  • If something is wrong, the cell can pause or start repairs.

• Cyclins and CDKs:

  • Cyclins are proteins that change amounts during the cell cycle. They activate other proteins called CDKs to help the cell move forward.
  • For example, a Cyclin B-CDK complex is very important for the cell to move from G2 to mitosis.

• Apoptosis:

  • If a cell has damaged DNA and can’t be fixed, it may undergo a process called programmed cell death (apoptosis) instead of dividing.
  • This prevents unhealthy cells from multiplying.

Conclusion

In conclusion, mitosis is a carefully organized process that makes sure a cell divides correctly to produce two identical daughter cells. It is controlled by checkpoints, cyclins, CDKs, and processes like apoptosis, which help keep cells healthy. Understanding mitosis and how it is controlled is essential for knowing how living things grow and repair their tissues!