Centromere: Definition & Structure

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  • 0:01 Definition of a Centromere
  • 0:21 Centromere Functions
  • 2:07 Centromere Localization
  • 3:52 Centromere Structure
  • 5:30 Lesson Summary
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Lesson Transcript
Instructor: Katy Metzler

Katy teaches biology at the college level and did her Ph.D. work on infectious diseases and immunology.

Eukaryotic chromosomes use special non-coding DNA sequences to carry out important tasks. In this lesson, you'll learn about one of these sequences, the centromere, and its roles in making sure chromosomes separate properly into daughter cells.

Definition of Centromere

In eukaryotes, a centromere is a region of DNA that is responsible for the movement of the replicated chromosomes into the two daughter cells during mitosis and meiosis. There is one centromere on each chromosome, and centromeres are responsible for two major functions.

Centromere Functions

One major function of a centromere is joining the sister chromatids. The two copies of a replicated chromosome are called sister chromatids, and they must stay joined together until it is time for them to be physically pulled into the two future daughter cells. This ensures that each daughter cell will get exactly one copy of each chromosome.

Cohesins are proteins that keep the chromatids stuck together. At the beginning of mitosis, the cohesins are distributed evenly along the chromatids, so they are stuck together along their whole lengths. By metaphase, when all the chromosomes are lined up at the middle of the cell just before they separate, the cohesins are only located at the centromere regions, so the sister chromatids are only connected there. In this diagram, you can see what this looks like.

The other major function of the centromere is attaching the microtubules in the mitotic spindle. In this function, the centromere directs the formation of the kinetochore, which is a special protein structure that attaches to the microtubules in the mitotic spindle. On each chromatid, the kinetochore forms at the centromere region of the DNA. Once all of the chromatids are attached to the mitotic spindle, the microtubules pull the sister chromatids apart into the two future daughter cells.

With this information, you can see why it's so important that each chromosome has exactly one centromere. If a chromosome had two centromeres, it could be broken apart by being pulled in two different directions during mitosis. If it had no centromeres, it would assort randomly into the daughter cells and would eventually be lost.

Centromere Localization

On a condensed, duplicated chromosome it is easy to see where the centromere is located. It's the part where the two chromatids are connected and form an X shape. Even on a single condensed chromosome, the centromere forms a constriction that can be seen in the microscope. 'Centro' means center and 'mere' means part, but centromeres are not always located right at the center of a chromosome. They can have various different positions, as shown in this diagram.

When the centromere is approximately in the center of a chromosome, it is called metacentric. 'Meta' means middle, so this makes sense. Submetacentric centromeres are closer to one end of the chromosome than the other. Their name means that they are not quite at the middle. Centromeres that are very close to one end of the chromosome are called acrocentric. 'Acro' means top or extremity. Telocentric centromeres are positioned at the very end of a chromosome. 'Telo' means last or end. You can compare this word to 'telomeres,' which are specialized regions of DNA at the very ends of chromosomes.

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