Mitosis: Metaphase, Anaphase And Telophase
Mitosis is the process in which a cell breaks apart its chromosome to eventually produce two identical daughter cells. The cell spends 10% of its time in mitosis. The cell goes through four stages in order to complete this task. The stages are Prophase, Metaphase, Anaphase and Telophase. Mitosis only occurs in eukaryotic cells and the process is different for different species. Mitosis is fast and very complex.
The first phase is Prophase. In prophase, the chromosomes the chromosomes start to coil, shorten, and become distinct. The nucleoli disappear and each replicated chromosomes appear as the identical sister chromatids join together. The spindle fibers begin to form and it`s made of the centrosomes and the microtubules that extend from …show more content…
them. The centrosomes move away from each other, propelled by the microtubules between them. The chromosomes are held together by centromeres. Centrosomes are very important in mitosis; the centrosomes will be pushed apart to opposite ends of the cell nucleus by the action of molecular motors acting on the microtubules. Basically, the chromatin in the nucleus coils into chromosomes. The nucleolus disintegrates and the centrosomes move to opposite poles of the cell, forming a bridge of spindle fibers. When prophase is complete, the cell moves o metaphase.
Second is Metaphase; Metaphase is longest stage of mitosis, lasting about 20 minutes.
The centrosomes are now at opposite ends of the cell. The chromosomes convene on the metaphase plate, an imaginary plane that is equidistant between the spindle`s the poles. The chromosomes centromeres lie on the metaphase plane. Each chromosome, the kinetochores of the sister chromatids are attached to kinetochore microtubules coming from the opposite poles. A cell cannot enter anaphase unless all the chromosomes have aligned themselves. The line in which the chromosome line up is called the spindle equator. When metaphase is completed, the cell moves to …show more content…
anaphase.
The third phase is Anaphase, where the chromosomes split and the sister chromatids move to opposite ends of the pole. Each chromatid becomes a full-fledged chromosome. Anaphase accounts for ~1% of the cell cycles time. The cell elongates as the nonkinetochore microtubules lengthen. Cohesion, which is a protein that is responsible for holding the sister chromatids is released and broken down to allow them to separate. While the chromosomes are drawn to each side of the cell, the non-kinetochore spindle fibers push against each other, in a ratcheting action, which stretches the cell into an oval. When anaphase is complete, the cell moves to Telophase.
The fourth stage is Telophase, where the effects of prophase are reversed.
Two daughter nuclei form in each daughter cell, forming nuclear envelopes around each nucleus. There are two theories as to how this happens: vesicle fusion-when fragments of the nuclear membrane fuse to rebuild the nuclear membrane. Reshaping of the endoplasmic reticulum-where the parts of the ER containing absorbed nuclear membrane envelop the nuclear space, reforming closed membrane. The chromosomes are become less condensed. As the nuclear membranes re-form around each set of chromatids, the nucleoli also reappear. The chromosomes also unwind back into the expanded chromatin that is present during interphase. Telophase accounts for approximately 2% of the cell cycle 's duration. Chromosomes are uncoiled from spindle fibers and lengthened. Spindle fibers degenerate. The division of one nucleus into toe genetically identical nuclei, is now
complete. ‘’ AsTomomi Kiyomitsu, a postdoctoral researcher in Whitehead Member Iain Cheeseman’s lab,watched mitosis unfold in symmetrically dividing human cells, he noticed that when the spindle oscillates toward the cell’s center, a partial halo of the protein dynein lines the cell cortex (a layer of proteins covering the inside of the cell membrane) on the side farther away from the spindle. Kiyomitsu determined that the motor protein dynein is anchored to the cell cortex by a complex that includes the protein LGN, short for leucine-glycine-asparagine-enriched protein. The stationary dynein acts as a winch to pull on the spindle pole, and the microtubules and chromosomes attached to it, toward the cell cortex. Kiyomitsu found that when a spindle pole comes within close proximity to the cell cortex, a signal from a protein called Polo-like kinase 1 (Plk1) emanates from the spindle pole, knocking dynein off of LGN and the cell cortex, stopping the spindle pole’s forward motion, and freeing dynein to move to the opposite side of the cell. Kiyomitsu also noticed that a layer of LGN extends all around the cell cortex, except in the areas that are closest to the chromosomes. After testing a couple of signaling molecules associated with chromosomes, Kiyomitsu determined that a signal from the chromosomes, involving the ras-related nuclear protein (Ran), blocks LGN, and therefore dynein, from attaching to the cell cortex closest to the chromosomes. His work suggests a key role for Ran in directing spindle orientation. The process of mitotic cell division has been studied intensely for more than 50 years. Using fluorescence microscopy, today’s scientists can see the tug-of-war cells undergo as they move through mitosis. Thread-like proteins, called microtubules, extend from one of two spindle poles on either side of the cell and attempt to latch onto the duplicated chromosomes. This entire “spindle” structure acts to physically distribute the chromosomes, but it is not free floating in the cell. In addition to microtubules from both spindle poles that attach to all of the chromosomes, astral microtubules that are connected to the cell cortex; a protein layer lining the cell membrane; act to pull the spindle poles back and forth within the cell until the spindle and chromosomes align down the center axis of the cell. Then the microtubules tear the duplicated chromosomes in half, so that ultimately one copy of each chromosome ends up in each of the new daughter cells.
REFERENCES http://01.edu-cdn.com/files/static/mcgrawhillprof/9780071623247/MITOSIS_01.GIF http://biology.clc.uc.edu/courses/bio104/mitosis.htm
Campbell, Neil A., Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, and Robert B. Jackson. AP Edition Biology. New York: Benjamin/Cummings, 2008. Print.
"Mitosis -." Wikipedia, the Free Encyclopedia. N.p., n.d. Web. 21 Sept. 2013. .
http://wi.mit.edu/news/archive/2012/mitosis-mystery-solved-how-chromosomes-align-perfectly-dividing-cell
The first phase is Prophase. In prophase, the chromosomes the chromosomes start to coil, shorten, and become distinct. The nucleoli disappear and each replicated chromosomes appear as the identical sister chromatids join together. The spindle fibers begin to form and it`s made of the centrosomes and the microtubules that extend from …show more content…
them. The centrosomes move away from each other, propelled by the microtubules between them. The chromosomes are held together by centromeres. Centrosomes are very important in mitosis; the centrosomes will be pushed apart to opposite ends of the cell nucleus by the action of molecular motors acting on the microtubules. Basically, the chromatin in the nucleus coils into chromosomes. The nucleolus disintegrates and the centrosomes move to opposite poles of the cell, forming a bridge of spindle fibers. When prophase is complete, the cell moves o metaphase.
Second is Metaphase; Metaphase is longest stage of mitosis, lasting about 20 minutes.
The centrosomes are now at opposite ends of the cell. The chromosomes convene on the metaphase plate, an imaginary plane that is equidistant between the spindle`s the poles. The chromosomes centromeres lie on the metaphase plane. Each chromosome, the kinetochores of the sister chromatids are attached to kinetochore microtubules coming from the opposite poles. A cell cannot enter anaphase unless all the chromosomes have aligned themselves. The line in which the chromosome line up is called the spindle equator. When metaphase is completed, the cell moves to …show more content…
anaphase.
The third phase is Anaphase, where the chromosomes split and the sister chromatids move to opposite ends of the pole. Each chromatid becomes a full-fledged chromosome. Anaphase accounts for ~1% of the cell cycles time. The cell elongates as the nonkinetochore microtubules lengthen. Cohesion, which is a protein that is responsible for holding the sister chromatids is released and broken down to allow them to separate. While the chromosomes are drawn to each side of the cell, the non-kinetochore spindle fibers push against each other, in a ratcheting action, which stretches the cell into an oval. When anaphase is complete, the cell moves to Telophase.
The fourth stage is Telophase, where the effects of prophase are reversed.
Two daughter nuclei form in each daughter cell, forming nuclear envelopes around each nucleus. There are two theories as to how this happens: vesicle fusion-when fragments of the nuclear membrane fuse to rebuild the nuclear membrane. Reshaping of the endoplasmic reticulum-where the parts of the ER containing absorbed nuclear membrane envelop the nuclear space, reforming closed membrane. The chromosomes are become less condensed. As the nuclear membranes re-form around each set of chromatids, the nucleoli also reappear. The chromosomes also unwind back into the expanded chromatin that is present during interphase. Telophase accounts for approximately 2% of the cell cycle 's duration. Chromosomes are uncoiled from spindle fibers and lengthened. Spindle fibers degenerate. The division of one nucleus into toe genetically identical nuclei, is now
complete. ‘’ AsTomomi Kiyomitsu, a postdoctoral researcher in Whitehead Member Iain Cheeseman’s lab,watched mitosis unfold in symmetrically dividing human cells, he noticed that when the spindle oscillates toward the cell’s center, a partial halo of the protein dynein lines the cell cortex (a layer of proteins covering the inside of the cell membrane) on the side farther away from the spindle. Kiyomitsu determined that the motor protein dynein is anchored to the cell cortex by a complex that includes the protein LGN, short for leucine-glycine-asparagine-enriched protein. The stationary dynein acts as a winch to pull on the spindle pole, and the microtubules and chromosomes attached to it, toward the cell cortex. Kiyomitsu found that when a spindle pole comes within close proximity to the cell cortex, a signal from a protein called Polo-like kinase 1 (Plk1) emanates from the spindle pole, knocking dynein off of LGN and the cell cortex, stopping the spindle pole’s forward motion, and freeing dynein to move to the opposite side of the cell. Kiyomitsu also noticed that a layer of LGN extends all around the cell cortex, except in the areas that are closest to the chromosomes. After testing a couple of signaling molecules associated with chromosomes, Kiyomitsu determined that a signal from the chromosomes, involving the ras-related nuclear protein (Ran), blocks LGN, and therefore dynein, from attaching to the cell cortex closest to the chromosomes. His work suggests a key role for Ran in directing spindle orientation. The process of mitotic cell division has been studied intensely for more than 50 years. Using fluorescence microscopy, today’s scientists can see the tug-of-war cells undergo as they move through mitosis. Thread-like proteins, called microtubules, extend from one of two spindle poles on either side of the cell and attempt to latch onto the duplicated chromosomes. This entire “spindle” structure acts to physically distribute the chromosomes, but it is not free floating in the cell. In addition to microtubules from both spindle poles that attach to all of the chromosomes, astral microtubules that are connected to the cell cortex; a protein layer lining the cell membrane; act to pull the spindle poles back and forth within the cell until the spindle and chromosomes align down the center axis of the cell. Then the microtubules tear the duplicated chromosomes in half, so that ultimately one copy of each chromosome ends up in each of the new daughter cells.
REFERENCES http://01.edu-cdn.com/files/static/mcgrawhillprof/9780071623247/MITOSIS_01.GIF http://biology.clc.uc.edu/courses/bio104/mitosis.htm
Campbell, Neil A., Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, and Robert B. Jackson. AP Edition Biology. New York: Benjamin/Cummings, 2008. Print.
"Mitosis -." Wikipedia, the Free Encyclopedia. N.p., n.d. Web. 21 Sept. 2013. .
http://wi.mit.edu/news/archive/2012/mitosis-mystery-solved-how-chromosomes-align-perfectly-dividing-cell