Division of a Cell Nucleus

Instructor: Dominic Corsini
How do cells replicate themselves? How do they copy their DNA into new cells? In this lesson, we will explore the division of a cell nucleus. Test your knowledge after the lesson with a quiz.

What is a Cell Nucleus?

Most people know that they're made of cells. However, did you know that your cells are structurally different than cells in bacteria? That's because the cells in your body contain a nucleus while the cells in bacteria do not. The nucleus is the membrane-bound organelle inside a cell that holds DNA, our genetic material. In order for your cells to reproduce they must be capable of dividing into new cells. This means they must be able to divide the nucleus. This occurs during a process called mitosis. Mitosis is the process of splitting the cell's genetic material into two new nuclei. To understand the bigger picture, we need to recognize how mitosis fits into the cell's life cycle.

The Cell Cycle

Scientists refer to the series of events occurring during the cell's life as the cell cycle. This cycle consists of four major phases: the G1, S, G2 and M phases. Each of these phases is important to the cell, but S phase and M phase are especially vital to division of the cell nucleus. S phase is when DNA is replicated. M phase, also referred to as mitosis, is when the cell nucleus actually divides into two new cells. Below you'll find a diagram of the cell cycle.

Cell Cycle
Cell Cycle

How the Nucleus Divides

Division of the cell nucleus occurs during multiple steps. When studying this division, people often focus only on M phase of the cell cycle. This is understandable since M phase is when the actual division takes place. However, to understand division we cannot overlook S phase. S phase, also known as synthesis, is when DNA is replicated. This is vital to the process of division because without replication cells cannot provide each new cell with adequate amounts of DNA. Therefore, as we begin examining how M phase works, please remember that we're working with two sets of identical DNA that were created during S phase.

As aforementioned, M phase is also called mitosis. If you remember, mitosis is the process of dividing a cell's genetic material (DNA) into two new nuclei. The process of mitosis is generally subdivided into multiple steps. Have a look at the image below.


The initial part of this image represents S phase, where DNA is replicated. Notice how each chunk of our hypothetical DNA doubles in size following replication. The shape of the DNA within our illustration represents two different chromosomes. Chromosomes are structures built from DNA that contain the instructions for making a living organism. Humans have 46 chromosomes, so this illustration is simplified to provide clarity.

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