Prometaphase
McGraw-Hill Science & Technology Dictionary:
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prometaphase
(prō′med·ə′fāz)
(cell and molecular biology) A stage between prophase and metaphase in mitosis in which the nuclear membrane disappears and the spindle forms.
American Heritage Stedman's Medical Dictionary:
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pro·met·a·phase
(prō-mĕt'ə-fāz')
n.
n.
The stage of mitosis or meiosis in which the nuclear membrane disintegrates, the centrioles reach the poles of the cell, and the chromosomes continue to contract.
Oxford Dictionary of Biochemistry:
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prometaphase
the stage in mitosis or meiosis, following prophase, during which the nuclear envelope is disrupted and breaks into membrane vesicles, and the spindle microtubules enter the nuclear region. Kinetochores mature on each centromere and attach to some of the spindle microtubules; these are then called kinetochore microtubules while those to which kinetochores do not attach are called polar microtubules; microtubules outside the spindle are called astral microtubules. Kinetochore microtubules begin the process of aligning chromosomes in one plane halfway between the poles.
| prolyl oligopeptidase, prolyl, prolixin-S | |
| promiscuous DNA, promoter, promoter escape |
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Prometaphase
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This article does not cite any references or sources. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (May 2009) |
Prometaphase is the phase of mitosis following prophase and preceding metaphase, in eukaryotic somatic cells. Prometaphase is sometimes simply included as part of the end of prophase and early metaphase.
In Prometaphase, the nuclear membrane breaks apart into a bunch of "membrane vesicles". Microtubules emerging from the centrosomes at the poles (ends) of the spindle reach the chromosomes, now highly condensed. At the centromere region, each sister chromatid has a protein structure called a kinetochore. Some of the spindle microtubules attach to the kinetochores, throwing the chromosomes into agitated motion. Other spindle microtubules make contact with microtubules coming from opposite pole. Forces exerted by protein "motors" associated with spindle microtubules move the chromosomes toward the center of the cell.
Open and closed mitosis
In "open mitosis", microtubules which have radiated from the two centrosomes located at the opposite poles of the cells invade the nuclear space as the nuclear membrane disassembles. This allows the microtubules to reach for the chromosomes and attach to their kinecticores.
Most fungi and many protists, such as algae, undergo a variation called "closed mitosis" where the microtubules are able to penetrate an intact nuclear envelope through a spindle pole body.
Metaphase, the next step in mitosis, is where the chromosomes align.
Types of microtubules
The microtubules are composed of two types, kinetochore microtubules and non-kinetochore microtubules.
- Kinetochore microtubules begin searching for kinetochores to attach to.
- A number of non-kinetochore microtubules or polar microtubules find and interact with corresponding nonkinetochore microtubules from the opposite centrosome to form the mitotic spindle.
Transition from prometaphase to metaphase
The role of prometaphase is completed when all of the kinetochore microtubules have attached to their kinetochores, upon which metaphase begins. An unattached kinetochore, and thus a non-aligned chromosome, even when most of the other chromosomes have lined up, will trigger the spindle checkpoint signal. This prevents premature progression into anaphase by inhibiting the anaphase-promoting complex until all kinetochores are attached and all the chromosomes aligned.
Early events of metaphase can coincide with the later events of prometaphase, as chromosomes with connected kinetochores will start the events of metaphase individually before other chromosomes with unconnected kinetochores that are still lingering in the events of prometaphase.
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McGraw-Hill Science & Technology Dictionary
McGraw-Hill Dictionary of Scientific and Technical Terms. Copyright © 2003, 1994, 1989, 1984, 1978, 1976, 1974 by McGraw-Hill Companies, Inc. All rights reserved.
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The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company.
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Oxford Dictionary of Biochemistry
Oxford University Press. Oxford Dictionary of Biochemistry and Molecular Biology © 1997, 2000, 2006 All rights reserved.
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