Prometaphase: Definition & Concept

Lesson Transcript
Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

Have you ever heard of prometaphase? Some texts avoid this term, but this lesson goes over the six key events that occur during this specific phase of mitosis.

What Is Prometaphase?

Don't you hate it when one science textbook tells you one thing and another science textbook doesn't even mention that one thing at all? Science is hard enough to understand, but it becomes even more confusing when scientists can't come to a consensus on what to call or label something. Such is the case with prometaphase, the phase of mitosis that begins when the nuclear envelope starts to break down.

Some textbooks identify prometaphase as a distinct phase of mitosis, the part of the cell cycle that involves the separation of chromosomes and other cellular constituents into two daughter cells. Other textbooks completely avoid mentioning prometaphase as a term. Instead, they include the concepts involved in prometaphase as a part of late prophase or late prophase and early metaphase. So just keep that tidbit in mind in case you are cross-referencing things.

In any case, this lesson focuses on prometaphase as a distinct phase of the cell cycle. Just know that as described herein, prometaphase of mitosis follows open mitosis, which applies to plants and animals. Closed mitosis, which applies to the likes of yeast and slime molds, is not discussed.

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  • 0:02 What Is Prometaphase?
  • 1:20 Early Prometaphase
  • 3:22 Late Prometaphase
  • 4:24 Lesson Summary
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Early Prometaphase

The difference between the two lies, in part, with the nuclear envelope. In closed mitosis, chromosome separation occurs in an intact nuclear envelope. In open mitosis, the chromosomes separate after the nuclear envelope disintegrates. That latter sentence should remind you of our definition for prometaphase, as it is a phase of mitosis that begins when the nuclear envelope disassembles into vesicles and begins to sort of look like the smooth endoplasmic reticulum as it does so. If it hasn't already, prior to prometaphase, the nucleolis completely disappears at this point as well. Thus, the first part of early prometaphase involves the disassembly of the nuclear envelope.

The nuclear envelope now looks like a really old t-shirt full of holes and tears. While not pretty, it's pretty important. That's because the holes allow for the penetration of the nuclear envelope by microtubules, cylindrical structures made of a protein called tubule, which supports cellular structures and functions as tracks for the movement of intracellular components. These microtubules grow from the spindle poles towards the nuclear envelope and penetrate the envelope, so the second part of early prometaphase involves the growth of microtubules.

Once the microtubules make their way into the disintegrating nuclear envelope, they superglue themselves onto structures called kinetochores, button-like protein-based structures located on the surface of the centromere. The centromere is a structure that holds together the two sister chromatids of a replicated chromosome. Each sister chromatid has its own kinetochore located at opposite sides of the chromosome. Thus, the third part of early prometaphase involves the attachment of microtubules to kinetochores.

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