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Mitosis

Cytokinesis

Cell division is not finished, however. During cytokinesis, the cytoplasm of a cell is physically divided to form two daughter cells housing the newly formed nuclei. In addition to dividing up the cytoplasm, cytokinesis distributes cellular organelles equally to the daughter cells. The binding of some molecules or organelles to the chromosomes or spindle microtubules ensures that each daughter cell will receive a fair share of cytoplasmic components.

A belt of microfilaments constricts the cell, pinching it in two. In plants, a cell plate forms, growing outward until it reaches the cell membrane and fuses with it. Cellulose is laid down on the new membranes, forming a strong new cell wall.

Resources

Books

Arms, Karen, and Pamela S. Camp. Biology. 3rd ed. Philadelphia: Saunders College Publishing, 1987.

Beck, William S., Karel F. Liem, and George G. Simpson. Life, an Introduction to Biology. 3rd ed. New York: Harper-Collins, 1991.

Campbell, N., J. Reece, and L. Mitchell. Biology. 5th ed. Menlo Park: Benjamin Cummings, Inc. 2000.

Starr, Cecie, and Ralph Taggart. Biology, The Unity and Diversity of Life. Belmont, CA: Wadsworth Publishing Company, 1992.

Elaine Friebele

KEY TERMS

Centriole: —An arrangement of microtubules found in most animal cells and in cells of some lower plants and fungi.
Centromere: —A constricted region of the chromosome joining two sister chromatids. The centromere is composed of highly repeated DNA sequences approximately 220 units in length.
Chromatin: —The name given to loose tangle of DNA strands in the nuclei of cells during periods when they are not dividing. As a cell prepares to divide, chromatin strands condense into compact chromosomes.
Chromosomes: —Structures in the eukaryotic cell nucleus consisting of heavily coiled DNA and proteins and carrying genetic information.
Cytokinesis: —The physical division of the cytoplasm of a eukaryotic cell to form two daughter cells, each housing a newly formed nuclei.
Cytoskeleton: —A network of assorted protein filaments attached to the cell membrane and to various organelles that makes up the framework for cell shape and movement.
DNA: —Strands of DNA, or deoxyribonucleic acid, are like long sentences of words composed of a four letter alphabet of nucleotide base pairs: A (adenine); T (thymine); G (guanine); and C (cytosine). The "words" contain the instructions for sequences of amino acids making up proteins.
Eukaryotic cell: —A cell whose genetic material is carried on chromosomes inside a nucleus encased in a membrane. Eukaryotic cells also have organelles that perform specific metabolic tasks and are supported by a cytoskeleton which runs through the cytoplasm, giving the cell form and shape. In contrast, the more primitive prokaryotic cells are smaller than eukaryotes, and have no nucleus, distinct organelles, or cytoskeleton.
Kinetochore: —A disk of protein bound to the centromere to which microtubules attach during mitosis, linking each chromatid to the spindle.
Microtubule: —A hollow protein cylinder, about 25 nanometers in diameter, composed of subunits of the protein tubulin. Microtubules grow in length by the addition of tubulin subunits at the end and are shortened by their removal.
Nucleotide: —The "letters" or basic units of DNA, containing a phosphate group, a 5-carbon sugar, and a ring-shaped nitrogenous base.
Spindle apparatus: —An axis of microtubules formed between centrioles in animal cells that aids the equal distribution of chromosomes to new cells being formed.

Additional topics

Science EncyclopediaScience & Philosophy: Methane to Molecular clockMitosis - Prophase, Anaphase, Cytokinesis - Metaphase, Telophase