DNA replication and thus chromosome duplication occurs during the interphase , the part of the cell cycle in which the cell is not dividing. It is important to know that the interphase is not part of mitosis. Here is your typical cell cycle:. As shown here, DNA replicates during the S phase synthesis phase of interphase , which is not part of the mitotic phase. When DNA replicates, a copy of each chromosome is produced, so chromosomes duplicate. During which stage of mitosis do chromosomes duplicate?
Henry W. During prometaphase, the nuclear membrane disintegrates and the mitotic spindle gains access to the chromosomes. During this phase, a protein structure called the kinetochore is associated with the centromere on each sister chromatid. Stringlike structures called microtubules grow out from the spindle and connect to the sister chromatids at their kinetochores; one microtubule from one side of the spindle attaches to one sister chromatid in each chromosome, and one microtubule from the other side of the spindle attaches to the other sister chromatid Figure 3a.
Figure 3: a Metaphase and b Anaphase. In metaphase a , the microtubules of the spindle white have attached and the chromosomes have lined up on the metaphase plate.
During anaphase b , the sister chromatids are pulled apart and move toward opposite poles of the cell. Figure Detail. After metaphase is complete, the cell enters anaphase. During anaphase, the microtubules attached to the kinetochores contract, which pulls the sister chromatids apart and toward opposite poles of the cell Figure 3c.
At this point, each chromatid is considered a separate chromosome. Figure 4: During telophase, two nuclear membranes form around the chromosomes, and the cytoplasm divides. Finally, once anaphase is complete, the cell enters the last stage of the division process — telophase.
During telophase, the newly separated chromosomes reach the mitotic spindle and a nuclear membrane forms around each set of chromosomes, thus creating two separate nuclei inside the same cell. As Figure 4 illustrates, the cytoplasm then divides to produce two identical cells. Why is mitosis important? As previously mentioned, most eukaryotic cells that are not involved in the production of gametes undergo mitosis. These cells, known as somatic cells , are important to the survival of eukaryotic organisms, and it is essential that somatic parent and daughter cells do not vary from one another.
With few exceptions, the mitotic process ensures that this is the case. Therefore, mitosis ensures that each successive cellular generation has the same genetic composition as the previous generation, as well as an identical chromosome set.
Watch this historic video from to see mitosis in action. Key Questions How do centromeres work? Key Concepts chromosomes replication meiosis. Topic rooms within Genetics Close. No topic rooms are there. Browse Visually. Other Topic Rooms Genetics. Student Voices.
Thus, the amount of DNA in the cell has effectively doubled, even though the ploidy , or chromosome count, of the cell remains at 2 n. Note: Chromosomes double their number of chromatids post replication but the nuclei remains diploid as the number of centromeres and chromosomes remains unchanged. Hence, the number of chromosomes in the nucleus, which determines the ploidy, remains unchanged from the beginning to the end of the S phase.
Following S phase, the cell enters G 2 phase. During G 2 , the cell synthesizes a variety of proteins. Of particular significance to the cell cycle, most microtubules — proteins that are required during mitosis — are produced during G 2.
Not all cells are continually replicated.
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