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Video:What Is Mitosis?

with Jim Shields

Mitosis is the process by which eukaryotic cells split in order to form new cells. This video form About.com will teach you the phases of mitosis.See Transcript

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Transcript:What Is Mitosis?

Hi, I'm Jim Shields from About.com, and today I'm going to teach you about Mitosis. 

Definition of Mitosis

How do living things grow? When a snake sheds its skin, where does the new skin come from? We are made up of a collection of cells, and these cells need to reproduce. They do that through something called mitosis. Mitosis is the term for the cycle of asexual reproduction of a single "mother" cell into two "daughter" cells, which are identical in every way.

When we talk about a cycle, we are referring to a process that has a series of steps that happen over and over in a predictable order. Mitosis happens surprisingly quickly when you think about how many steps there are in the cycle. 

Mitosis Cycle: Interphase

The first step in mitosis is called interphase, and it is the step where the cell is growing before it divides into two identical cells. This step is important since the mother cell needs enough mass and genetic material to share equally with each of the twin daughter cells.

During interphase, the DNA is replicating, but it is still loosely organized strands called chromatin. During interphase, centrioles are produced. Centrioles are sets of microtubules, organized in a star-like configuration, which form outside of the nucleus of the cell. 

Mitosis Cycle: Prophase

Next comes prophase, when the cell begins organizing itself to divide. During this step, the replicated DNA gets organized into separate chromosomes. Each one of the chromosomes is made up of a pair of chromatids attached at the center by a centromere.

At the start of prophase, the nucleus is still intact to protect the DNA, but it begins to break down by the end to allow the separation of the chromosomes. Also during prophase, the centrioles move to opposite ends of the cell, sending out fibers that create a structure called the mitotic spindle. These fibers begin reaching out toward the center of the cell to attach to the chromosomes. 

Mitosis Cycle: Metaphase

This step is followed by metaphase. During metaphase, the spindle fibers attach to each chromosome at its centromere at a special place called the kinetocore. Each chromatid in the chromosome has its own kinetocore. The fibers start to align the chromosomes along the center of the cell in preparation for separation during anaphase. 

Mitosis Cycle: Anaphase

Anaphase is the next step, and it's about separating the genetic material. The centrioles use their spindle fibers to begin dragging the chromosomes to each side of the cell, equally dividing them into identical sets. At this point, the cell begins to elongate and stretch in preparation for telophase. 

Mitosis Cycle: Telophase

In telophase, now that all the DNA, in the form of chromosomes, is divided into the two ends of the cell, the cell membrane closes to divide itself into two new matching cells. After telophase, each of the new cells enters interphase again, replicating its genetic material and growing to prepare for a new cycle of reproduction. It's important to note that mitosis only happens in eukaryotic cells. 

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