Mitosis

The nuclear division followed by a cell division.

What are the stages of Mitosis?

The stages of Mitosis are Prophase, Metaphase, Anaphase, Telophase, and Cytokenesis.

What occurs during prophase?

During Prophase, the chromosomes start to condense, making them very compact and easy to pull apart. During this time, the mitotic spindle begins to form.

-The spindle is a structure made of microtubules, which are strong fibers that are part of the cell's skeleton. The spindles' job is to organize and move the chromosomes around during mitosis. The spindle grows between the centrosomes as they move apart.

The nucleolus disappears, which is a sign that the nucleus is getting ready to break down. The cell's nuclear envelope breaks down, releasing the chromosomes. The microtubules then bind to chromosomes at the kinetochore, a patch of protein found on the centromere of each sister chromatid.

-Centromeres are the regions of DNA where the sister chromatids are most tightly connected.

What occurs during Metaphase?

During Metaphase, the spindle has captured all the chromosomes in the cell and lined them up at the middle. All the chromosomes align at the metaphase plate.

-The metaphase plate is a term for the plane where the chromosomes line up.

At this time, the two kinetochores of each chromosome should attach to the microtubules from opposite spindle poles. But before moving to anaphase, the cell checks that all the chromosomes are at the metaphase plate. They inspect if the chromosomes are with their kinetochores correctly attached to microtubules.

-This is called the spindle checkpoint and helps ensure that the sister chromatids split evenly between the two daughter cells when they separate in the next step.

-If a chromosome is not correctly aligned or attach, the cell will halt division until the problem is solved.

What occurs during Anaphase?

During Anaphase, the sister chromatids separate from each other and are pulled towards opposite ends of the cell.

-The protein that holds the sister chromatids together breaks down to allow them to separate. In which each is now its chromosome.

-The chromosomes of each pair are pulled towards opposite ends of the cell.

The microtubules that are not attached to chromosomes elongate and push apart. Thus separating the poles and making the cell longer. All of these processes are handle by motor proteins. Motor proteins are molecular machines that can “walk” along microtubule tracks and carry cargo.

-In mitosis, motor proteins are essential because they carry chromosomes or other microtubules as they walk.

What occurs during Telophase?

During Telophase, the mitotic spindle breaks down into its building blocks, and two new nuclei form, one for each set of chromosomes. The nuclear membranes and nucleoli reappear, and the chromosomes begin to de-condense and return to their “stringy” form. This state of manner is known as chromatin.

What occurs during Cytokenesis?

During Cytokenesis, the cytoplasm divides to form two new cells. The new cells overlap with the final stages of mitosis.

-It can occur either in Anaphase or Telophase, depending on the cell. The process finishes shortly after Telophase.

In animal cells, Cytokinesis is contractile. It pinches the cell in two like a coin purse with a drawstring.

-The “drawstring” is a group of filaments made of a protein called actin. The pinch crease is known as the cleavage furrow.

Unlike animal cells, plant cells can’t be divide like this. It is due to their cell wall and their stiffness.

-Instead, a structure called the cell plate forms down the middle of the cell, splitting it into two daughter cells separated by a new wall.

When Cytokinesis finishes, we end up with two new cells, each with a complete set of chromosomes identical to those of the mother cell.

-The daughter cells can now begin their cellular “lives” and – depending on what they are – may undergo mitosis themselves, repeating the cycle.

Overview

Mitosis: the cell division that creates two genetically identical daughter cells.

- Mitosis processes are Prophase, Metaphase, Anaphase, Telophase, and Cytokenesis.

- During Prophase, the duplicated chromosomes condense and become visible as distinct sister chromatids. The nuclear envelope, the membrane surrounding the nucleus, breaks down, and the chromosomes move towards the poles of the cell. The mitotic spindle, made of microtubules, attach to a specialized structure called the kinetochore. The kinetochore is at the centromere of each replicated chromosome.

- During Metaphase, the replicated chromosomes align at the metaphase plate of the cell.

- During Anaphase, the sister chromatids separate. In which they move towards the opposite poles of the cell by the spindle. The movement causes the cell to elongate towards its poles.

- During Telophase, the cell continues to elongate, and the mitotic spindle breaks down. A new nuclear envelope forms at each end of the cell and the chromosomes within begin to unfold into chromatin.

- During Cytokenesis, the cytoplasm and organelles are evenly divided between the two new cells completing cell division. Yet cytokinesis differs with animal and plant cells. In animal cells, it is easier to pinch together to form two new cells. While in plant cells, it is harder to grasp together to create two new cells. It's more intricate due to the cell's wall and its stiffness.