Phases of Mitosis — Definition

Definition

Imagine your body needs to grow, or you get a cut and your skin needs to heal. How does your body make more cells? It uses a process called mitosis! Mitosis is like a carefully choreographed dance that a cell performs to make two exact copies of itself.

It's how one 'parent' cell divides into two 'daughter' cells that are genetically identical to the parent and to each other. This process is super important for almost all living things to grow, replace old or damaged cells, and even for some organisms to reproduce without a partner.

Before mitosis even begins, the cell spends most of its life in a stage called Interphase. During Interphase, the cell grows, carries out its normal functions, and most importantly, duplicates all its genetic material (DNA). So, by the time mitosis starts, each chromosome in the cell has already made an identical copy of itself, and these two copies, called sister chromatids, are joined together.

Mitosis itself is divided into four main acts, or phases, which flow seamlessly into one another:

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Prophase (The Preparation Phase): — Think of this as the cell getting ready for the big show. The long, thread-like DNA, which was spread out like spaghetti in a bowl, starts to coil up and condense. It becomes super compact and visible under a microscope as distinct chromosomes. The nuclear envelope, which is like the membrane surrounding the cell's nucleus, starts to break down. Also, tiny structures called centrosomes (which help organize the cell's internal skeleton) move to opposite ends of the cell, and spindle fibers (made of microtubules) begin to form between them, like ropes stretching across the cell.

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Metaphase (The Middle Phase): — This is where everything lines up perfectly. The condensed chromosomes, each still made of two sister chromatids, move and align themselves precisely at the very center of the cell. This imaginary line is called the metaphase plate or equatorial plate. The spindle fibers, which are now fully formed, attach to a specific point on each sister chromatid called the kinetochore. It's like each chromosome is hooked onto a rope, ready to be pulled.

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Anaphase (The Apart Phase): — This is the dramatic moment of separation! The sister chromatids, which were once joined, finally pull apart. The spindle fibers shorten, effectively pulling one chromatid from each pair towards one pole of the cell and its identical sister chromatid towards the opposite pole. Now, each separated chromatid is considered a full-fledged chromosome. The cell temporarily has double the usual number of chromosomes, but they are rapidly moving to opposite ends.

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Telophase (The Two Nuclei Phase): — The cell starts to reverse the changes made during prophase. Once the chromosomes arrive at their respective poles, they begin to decondense, becoming less compact and returning to their thread-like chromatin form. New nuclear envelopes start to form around each set of chromosomes at the poles, creating two distinct nuclei within the single parent cell. The spindle fibers disappear.

Finally, after these four phases of nuclear division (karyokinesis), the cell's cytoplasm also divides in a process called Cytokinesis. In animal cells, the cell membrane pinches inward, forming a cleavage furrow, eventually splitting the cell into two. In plant cells, a new cell wall, called a cell plate, forms in the middle, growing outwards until it divides the cell. The result of mitosis and cytokinesis is two genetically identical daughter cells, each ready to begin its own life cycle.