Cell division is the process by which a cell splits into two or more daughter cells. Each new cell receives a complete set of genetic material that allows the organism to grow, repair damaged tissues, and reproduce. There are two main types of cell division: mitosis, which results in identical cells, and meiosis, which creates cells with unique combinations of genetic traits. This process is essential for the development and maintenance of life in all living organisms. In this blog, let us learn in detail about mitosis and the different phases of mitosis.
What is Mitosis?
Mitosis is a process where a cell’s nucleus divides into two, and then the parent cell splits into two identical daughter cells. The word “mitosis” means “threads,” which describes the thread-like shape of chromosomes before cell division. Earlier scientists noticed this structure in a microscope and they also saw a network of tiny tubes called spindles that help with the division process. These spindles grow from areas called centrosomes and play a key role in splitting the cell.
During mitosis, two centrosomes will be at opposite ends of the cell. When the mitosis process happens, microtubules attach to the chromosomes, which have already copied their DNA and lined up in the middle of the cell. The microtubules then shorten and move towards the cell’s ends by pulling one copy of each chromosome with them. This ensures that each new cell gets an exact copy of the original cell’s DNA.
Mitosis is a process that helps living things grow and replace old or damaged cells. In simple organisms like yeast, mitosis creates new individuals. In humans, mitosis helps bodies grow and repair themselves by creating new cells.
What are the Phases of Mitosis?
Before a cell divides or the phases of mitosis begin, it goes through a growth period called Interphase, which takes up about 90% of its life cycle. Interphase has three stages:
G1 (first gap phase): The cell grows and prepares for division.
S (synthesis phase): The cell copies its DNA.
G2 (second gap phase): The cell makes more proteins and grows some more.
After interphase, the cell enters mitosis, which has five stages: Prophase, Prometaphase, Metaphase, Anaphase, and Telophase. During these stages, the chromosomes line up and separate. Finally, the cell splits into two through a process called cytokinesis.
Here, let us take a look at the various stages of mitosis.
Prophase
Prophase is the initial stage of mitosis. It will happen after the cell has finished growing in the G2 phase. During this stage, the parent cell’s chromosomes, which were duplicated during the S phase, will undergo condensation. This condensation process will transform the chromosomes into X-shaped structures that will be visible under a microscope. Each X-shaped structure will consist of two identical sister chromatids joined at a point called the centromere.
Special proteins called cohesin and condensin will help the condensation process. Cohesin will form rings that hold the sister chromatids together, while condensin will create rings that coil the chromosomes into tight forms.
As prophase continues, a structure called the mitotic spindle will form. The two centrosomes will move to opposite ends of the cell, and microtubules will grow between them to create a network. This network will eventually separate the duplicated chromosomes and play a key role in cell division.
Prometaphase
During prometaphase, the second stage of mitosis, the nuclear membrane will break down into small vesicles due to the action of certain enzymes. This breakdown will allow the spindle microtubules to access the cell’s genetic material directly.
Each microtubule will be highly active and will extend outward from the centrosome and retract as it searches for a chromosome to attach to. Eventually, the microtubules will find their targets and will connect to the chromosomes at a specific region called the kinetochore, a complex of proteins that is located at the centromere.
The number of microtubules that will attach to a kinetochore can vary between species. However, microtubules from each end of the cell will typically connect to each chromosome’s kinetochore. This connection will cause the chromosomes to move back and forth between the two poles.
Metaphase
When the metaphase begins, the chromosomes will align at the center of the cell. Microtubules will attach to each chromosome, extending from its kinetochore, with at least one microtubule connecting to each end of the cell.
The cell’s internal tension will reach a state of balance. At this point, the chromosomes will stabilize and cease moving back and forth. Then, the spindle will fully form, and three distinct groups of spindle microtubules will become visible.
There will be three types of microtubules: kinetochore microtubules will connect the chromosomes to the spindle pole; interpolar microtubules will extend from the spindle pole to the equator and overlap with microtubules from the opposite pole; and astral microtubules will project from the spindle pole to the cell membrane.
Anaphase
Following metaphase, the cell will enter anaphase, where the sister chromatids of each chromosome will separate and move to opposite ends of the cell. To make this separation possible, Enzymes will break down cohesin, a protein that previously held the sister chromatids together. Once separated, each chromatid will become a distinct chromosome.
Concurrently, alterations in microtubule length will drive chromosome movement. Specifically, during the initial phase of anaphase (anaphase A), kinetochore microtubules will shorten, pulling chromosomes toward the spindle poles. Subsequently, in the next phase (anaphase B), astral microtubules anchored to the cell membrane will pull the poles apart, while interpolar microtubules will slide past each other, generating additional force to separate the chromosomes.
Telophase
In telophase, the chromosomes will arrive at the cell poles, and the mitotic spindle will disassemble. Vesicles containing fragments of the parent nuclear membrane will collect near the two sets of chromosomes. The lamins at each end of the cell will undergo phosphorylation by phosphatases, triggering the formation of a new nuclear membrane around each group of chromosomes. This process will effectively re-establish the nuclear envelope, enclosing the chromosomes within two separate nuclei.
Cytokinesis
Cytokinesis is the last stage in the mitosis process, where the parent cell will split into two identical daughter cells. This process will begin when the cell membrane pinches inward at the equator, creating a small opening called the cleavage furrow. Specific microtubules, namely astral and interpolar microtubules, which will have been established during anaphase, will determine the position of the furrow.
The cleavage furrow will form as a result of a contractile ring composed of overlapping actin and myosin filaments. As these filaments slide past one another, the ring will contract, much like tightening a drawstring. When the ring reaches its smallest point, the cleavage furrow will divide the cell into two halves, resulting in the creation of two separate daughter cells of equal size.
The process of cytokinesis differs between plants and animals. In animals, a band of contractile filaments constricts the cell. In plants, the cell creates a new cell wall between the two daughter cells by forming a cell plate. The Golgi apparatus produces tiny sacs that merge along the middle of the cell, forming a flat, disk-shaped structure that becomes the new cell wall.
Wrapping Up
By now, you will have gained a better knowledge of mitosis and its different stages. In case, you still require more details about mitosis or cell division processes, then contact a biology assignment expert from our team. The professionals on our platform are knowledgeable of different concepts related to botany and zoology and hence they can offer you cheap and the best biology assignment help to fetch top grades.
