cell division
Cell division consists of two processes: mitosis and cytokinesis. Mitosis— division of the nucleus and its chromosomes— is divided into five phases:prophase, prometaphase, metaphase, anaphase, and telophase. Mitosis is followed by cytokinesis, when the cytoplasm splits to form two separate daughter cells.
The cytoplasm of a cell in late interphase contains two centrosomes, each of which may contain a pair of centrioles. In the nucleus, the chromosomeshave been replicated during S phase, but are still dispersed in the form ofchromatin. One or more nucleoli are present.
During prophase, the nucleoli disappear and chromatin fibers coil up to become discrete chromosomes. Each chromosome consists of two identical sister chromatids, joined at the centromere. Microtubules grow out from the centrosomes, initiating formation of the mitotic spindle.
During prometaphase, the nuclear envelope breaks into fragments. Some of the spindle fibers reach the chromosomes and attach to kinetochores, structures made of proteins and specific sections of DNA at thecentromeres. Nonkinetochore microtubules overlap with those coming from the opposite pole.
At metaphase, the mitotic spindle is fully formed, and the microtubulesattached to kinetochores move the chromosomes to the metaphase plate, an imaginary plane equidistant from the poles.
Anaphase begins when the two centromeres of each chromosome come apart, separating the sister chromatids. Once separate, each sister chromatid is considered a full-fledged daughter chromosome. Motor proteins of the kinetochores "walk" the daughter chromosomes along thespindle microtubules toward opposite poles, and the microtubules shorten. At the same time, the spindle microtubules not attached to chromosomes lengthen, pushing the two poles farther apart and elongating the cell.
During telophase, nuclear envelopes form around the identical sets ofchromosomes at the two poles of the cell. The chromosomes uncoil andnucleoli appear in the two new
The cytoplasm of a cell in late interphase contains two centrosomes, each of which may contain a pair of centrioles. In the nucleus, the chromosomeshave been replicated during S phase, but are still dispersed in the form ofchromatin. One or more nucleoli are present.
During prophase, the nucleoli disappear and chromatin fibers coil up to become discrete chromosomes. Each chromosome consists of two identical sister chromatids, joined at the centromere. Microtubules grow out from the centrosomes, initiating formation of the mitotic spindle.
During prometaphase, the nuclear envelope breaks into fragments. Some of the spindle fibers reach the chromosomes and attach to kinetochores, structures made of proteins and specific sections of DNA at thecentromeres. Nonkinetochore microtubules overlap with those coming from the opposite pole.
At metaphase, the mitotic spindle is fully formed, and the microtubulesattached to kinetochores move the chromosomes to the metaphase plate, an imaginary plane equidistant from the poles.
Anaphase begins when the two centromeres of each chromosome come apart, separating the sister chromatids. Once separate, each sister chromatid is considered a full-fledged daughter chromosome. Motor proteins of the kinetochores "walk" the daughter chromosomes along thespindle microtubules toward opposite poles, and the microtubules shorten. At the same time, the spindle microtubules not attached to chromosomes lengthen, pushing the two poles farther apart and elongating the cell.
During telophase, nuclear envelopes form around the identical sets ofchromosomes at the two poles of the cell. The chromosomes uncoil andnucleoli appear in the two new