What Is Mitosis? | Let's Talk Science

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Ever wonder how your skin repairs itself when your scrape your knee? Or how a baby grows into an adult? These complicated processes start on a microscopic level, in your cells.

Cells are living things. They carry out life functions while they’re alive. And they eventually break down and die.

Each type of cell has a different life span. Some, like white blood cells, live for less than a day. Others, like the neurons in your brain, can last survive you entire life! But most of the cells in your body need to be replaced at some point.

Where do cells come from?

Cells are created through cell division. And mitosis is an important part of this process. Mitosis creates identical copies of cells. For example, it creates new skin cells to replace dead skin cells.

Misconception Alert

Gametes are the cells needed for reproduction. Unlike other cells, they are not produced through mitosis. Instead, sex cells are produced through meiosis.

Mitosis: The Amazing Cell Process that Uses Division to Multiply! (2016) by Amoeba Sisters (8:26 min.).

But before mitosis, cells go through interphase. In fact, interphase takes up about 90% of a cell’s life. That leaves just 10% for mitosis!

Cell before mitosis showing the location of the centrioles, microtubules, nuclear membrane, nucleolus, and DNA (Let’s Talk Science using an image by Aldona via iStockphoto).

Interphase has three stages: G1, S and G2. During the G1 stage, the cell prepares for division by increasing its mass. During the S stage, the cell synthesizes more DNA. And during the G2 stage, the cell synthesizes proteins as it continues to grow.

Before it can divide, a cell also needs to have its long uncoiled strands of DNA condensed into chromosomes. Otherwise, cell division would be like trying to split a plate of spaghetti in half. Chromosomes are made of bundles of DNA and protein. This makes them much easier to move around.

Graphic showing how the DNA double helix condenses to form chromosomes
Graphic showing how the DNA double helix condenses to form chromosomes (Source: Let’s Talk Science, adapted from illustration by KES47 via Wikimedia Commons).

Misconception Alert

Cells don’t always follow the process of mitosis. For example, genetic or environmental conditions can cause cancer, which leads to uncontrolled cell division.

Stages of Mitosis

Once interphase is complete, the cell is ready to go through the four stages of mitosis. The acronym “PMAT” can help you remember the different stages.

P is for prophase

Prophase is the first stage of mitosis. The cell’s nucleus remains, but the nucleolus disappears. The nucleolus is the envelope that holds the genetic material inside the nucleus.

Centrioles and microtubules make up the centrosomes. They move to opposite ends of the cell. Each end is called a pole. The microtubules begin to form the mitotic spindle. It attaches to the centrioles. The P in prophase can help you remember that the centrioles are now located at the cell’s poles.

Cell during prophase, showing the location of the centrioles, early microtubule spindles and chromosomes
Cell during prophase, showing the location of the centrioles, early microtubule spindles and chromosomes (Let’s Talk Science using an image by Aldona via iStockphoto).

M is for metaphase

When metaphase begins, the membrane of the nucleus dissolves. The mitotic spindle becomes fully formed and attaches to the centromeres of the chromosomes. The M in metaphase can help you remember that by the end of this phase, the spindles pull the chromosomes to the middle of the cell. This area is called the metaphase plate.

Cell during metaphase showing the location of the centrioles, spindles, chromosomes, nuclear membrane and metaphase plate
Cell during metaphase showing the location of the centrioles, spindles, chromosomes, nuclear membrane and metaphase plate (Let’s Talk Science using an image by Aldona via iStockphoto).

A is for anaphase

During anaphase, the mitotic spindle contracts. The two halves of the chromosomes—called chromatids—get pulled away from each other. This creates daughter chromosomes. The A in anaphase can help you remember that during this phase, the microtubules pull the daughter chromosomes away from each other and toward the poles. As a result, the cell gets begins to lengthen.

Cytokinesis also begins during anaphase. The cytoplasm starts to split apart as two new cells form.

Cell during anaphase showing the daughter chromosomes and how the cell begins to stretch out toward its poles
Cell during anaphase showing the daughter chromosomes and how the cell begins to stretch out toward its poles (Let’s Talk Science using an image by Aldona via iStockphoto).

T is for Telophase

During telophase, the daughter chromosomes reach the opposite poles of the cell. Two new nuclear membranes begin to form, one at each pole. The cell continues to elongate and begins to narrow at the centre. Both sets of chromosomes begin to relax and open up. The T in telophase can help you remember that at the end of this stage, there will be two new sets of genetic material.

Cell during anaphase showing the formation of two new nuclear membranes around the daughter chromosomes. The cell continues to stretch out toward its poles
Cell during anaphase showing the formation of two new nuclear membranes around the daughter chromosomes. The cell continues to stretch out toward its poles (Let’s Talk Science using an image by Aldona via iStockphoto).

Telophase also marks the end of cytokinesis. The cell breaks apart at the cleavage furrow. That’s the narrow point at the middle of the cell that started to form during anaphase. The cell divides into two identical daughter cells, each with its own nucleus and cytoplasm.

Cell after cytokinesis, showing the two identical daughter cells
Cell after cytokinesis, showing the two identical daughter cells (Let’s Talk Science using an image by Aldona via iStockphoto).

Understanding mitosis is important to understanding how organisms—like you!—grow and repair themselves. For example, when you cut your knee, skin cells start dividing to repair the damage. And just think of how many new cells your body has created since you were a baby!

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