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Most cell division results in genetically identical daughter cells

The genetic material (DNA) of a cell—its genome—is partitioned among chromosomes. Each eukaryotic chromosome consists of one DNA molecule associated with many proteins that maintain chromosome structure and help control the activity of genes. Together, the complex of DNA and associated proteins is called chromatin. The chromatin of a chromosome exists in different states of condensation at different times. In animals, gametes have one set of chromosomes and somatic cells have two sets.

Cells replicate their genetic material before they divide, ensuring that each daughter cell can receive a copy of the DNA. In preparation for cell division, chromosomes are duplicated, each one then consisting of two identical sister chromatids joined along their lengths by sister chromatid cohesion and held most tightly together at a constricted region at the centromeres of the chromatids. When this cohesion is broken, the chromatids separate during cell division, becoming the chromosomes of the new daughter cells. Eukaryotic cell division consists of mitosis (division of the nucleus) and cytokinesis (division of the cytoplasm).

The mitotic phase alternates with interphase in the cell cycle

Between divisions, a cell is in interphase: the G1, S, and G2 phases. The cell grows throughout interphase, but DNA is replicated only during the synthesis (S) phase. Mitosis and cytokinesis make up the mitotic (M) phase of the cell cycle.

The mitotic spindle is an apparatus of microtubules that controls chromosome movement during mitosis. In animal cells, the spindle arises from the centrosomes and includes spindle microtubules and asters. Some spindle microtubules attach to the kinetochores of chromosomes and move the chromosomes to the metaphase plate. In anaphase, sister chromatids separate, and motor proteins move them along the kinetochore microtubules toward opposite ends of the cell. Meanwhile, motor proteins push nonkinetochore microtubules from opposite poles away from each other, elongating the cell. In telophase, genetically identical daughter nuclei form at opposite ends of the cell.

• Mitosis is usually followed by cytokinesis. Animal cells carry out cytokinesis by cleavage, and plant cells form a cell plate

• During binary fission in bacteria, the chromosome replicates and the two daughter chromosomes actively move apart. Some of the proteins involved in bacterial binary fission are related to eukaryotic actin and tubulin.

• Since prokaryotes preceded eukaryotes by more than a billion years, it is likely that mitosis evolved from prokaryotic cell division. Certain unicellular eukaryotes exhibit mechanisms of cell division that may be similar to those of ancestors of existing eukaryotes. Such mechanisms might have been intermediate steps in the evolution of mitosis from bacterial binary fission.

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This book is dedicated to...

Gene Scronce

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Most cell division results in genetically identical daughter cells

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"The Cell Cycle"

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This book provides an overview of cell division, including mitosis, cytokinesis, and the eukaryotic cell cycle. It also discusses the regulation of the cell cycle and its implications in cancer.

(16 pages)

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