What is meant by the "division of the nucleus"? What do you think this colorful picture
shows? If you guessed that it’s a picture of a cell undergoing cell division, you are right. But more specifically, the image is a lung cell stained with fluorescent dyes undergoing mitosis, during early anaphase. During mitosis, when the nucleus divides, the two chromatids
that make up each chromosome separate from each other and move to opposite poles of the cell. This is shown in Figure below. You can watch an animation of the process at the following link:http://www.biology.arizona.edu/Cell_bio/tutorials/cell_cycle/MitosisFlash.html. Mitosis is the phase of the eukaryotic cell cycle that occurs between DNA replication and the formation of two daughter cells. What happens during mitosis? Mitosis actually occurs in four phases. The phases are called prophase, metaphase, anaphase, and telophase. They are shown in Figure below and described in greater detail in the following sections. Mitosis in the Eukaryotic Cell Cycle. Mitosis is the multi-phase process in which the nucleus of a eukaryotic cell divides. ProphaseThe first and longest phase of mitosis is prophase. During prophase, chromatin condenses into chromosomes, and the nuclear envelope, or membrane, breaks down. In animal cells, thecentrioles near the nucleus begin to separate and move to opposite poles (sides) of the cell. As the centrioles move, a spindle starts to form between them. The spindle, shown in Figurebelow, consists of fibers made of microtubules.
Spindle. The spindle starts to form during prophase of mitosis. Kinetochores on the spindle attach to the centromeres of sister chromatids. MetaphaseDuring metaphase, spindle fibers attach to the centromere of each pair of sister chromatids (see Figure below). The sister chromatids line up at the equator, or center, of the cell. This is also known as the metaphase plate. The spindle fibers ensure that sister chromatids will separate and go to different daughter cells when the cell divides. Chromosomes, consisting of sister chromatids, line up at the equator or middle of the cell during metaphase. AnaphaseDuring anaphase, sister chromatids separate and the centromeres divide. The sister chromatids are pulled apart by the shortening of the spindle fibers. This is like reeling in a fish by shortening the fishing line. One sister chromatid moves to one pole of the cell, and the other sister chromatid moves to the opposite pole. At the end of anaphase, each pole of the cell has a complete set of chromosomes. TelophaseDuring telophase, the chromosomes begin to uncoil and form chromatin. This prepares the genetic material for directing the metabolic activities of the new cells. The spindle also breaks down, and new nuclear membranes (nuclear envelope) form. CytokinesisCytokinesis is the final stage of cell division in eukaryotes as well as prokaryotes. During cytokinesis, the cytoplasm splits in two and the cell divides. Cytokinesis occurs somewhat differently in plant and animal cells, as shown in Figure below. In animal cells, the plasma membrane of the parent cell pinches inward along the cell’s equator until two daughter cells form. In plant cells, a cell plate forms along the equator of the parent cell. Then, a new plasma membrane and cell wall form along each side of the cell plate.
Cytokinesis is the final stage of eukaryotic cell division. It occurs differently in animal (left) and plant (right) cells. The phases of mitosis are discussed in the video: http://www.youtube.com/watch?v=LLKX_4DHE3I. The four phases of mitosis. Can you describe what happens in each phase? Summary
Explore MoreExplore More IUse this resource to answer the questions that follow.
Review
What is the phase where sister chromatids are pulled towards the opposite pole?Anaphase II: During anaphase II, the centromere splits, freeing the sister chromatids from each other. At this point, spindle fibers begin to shorten, pulling the newly-separated sister chromatids towards opposite ends of the cell.
Are sister chromatids pulled toward opposite poles in mitosis?Mitosis: In Summary
In anaphase, sister chromatids (now called chromosomes) are pulled toward opposite poles. In telophase, chromosomes arrive at opposite poles, and nuclear envelope material surrounds each set of chromosomes. Finally, in cytokenesis, the two daughter cells are separated.
During what phase of mitosis would the sister chromatids are separated and pulled to opposite poles of the cell by the spindle apparatus during a process called disjunction?During early anaphase, the sister chromatids begin to separate to opposite poles via kinetochore attachment to the spindle microtubules. Normally, sister kinetochores attach to microtubules with opposite orientations, known as amphitelic attachment.
Which stage of mitosis is occurring when sister chromatids are pulled towards opposite poles of the cell by the spindle apparatus?Anaphase. The sister chromatids separate from one another and are pulled towards opposite poles of the cell. The microtubules that are not attached to chromosomes push the two poles of the spindle apart, while the kinetochore microtubules pull the chromosomes towards the poles.
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