Chapt 8 Glossary

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Chapter 8

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GLOSSARY

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anaphase

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Of mitosis, stage when sister chromatids of each chromosome move to opposite spindle poles. Of anaphase I (meiosis), each duplicated chromosomes and its homologue move to opposite poles. Of anaphase II (meiosis), sister chromatids of each chromosome move to opposite poles.

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cell cycle

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Events by which a cell increases in mass, roughly doubles its cytoplasmic components, duplicates its DNA, then divides its nucleus and cytoplasm. Extends from the time a cell forms until it completes division.

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cell plate

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In a dividing plant cell, a disklike structure that becomes a crosswall with new plasma membrane on both sides.

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centriole

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Structure that gives rise to microtubules of cilia and flagella.

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centromere

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A constricted area of a chromosome that has attachment sites for spindle microtubules during nuclear division.

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chromosome

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[Gk. chroma, color, + soma, body] Of eukaryotic cells, a DNA molecule, duplicated or unduplicated, with many associated proteins. Of prokaryotic cells, a circular DNA molecule.

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chromosome number

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All chromosomes in a given type of cell. See haploidy; diploidy.

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cleavage furrow

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Ringlike depression defining cleavage plane for dividing animal cells.

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cytoplasmic division

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Cytokinesis; splitting of a parent cell into daughter cells.

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germ cell

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Animal cell of a lineage set aside for sexual reproduction; gives rise to gametes.

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HeLa cell

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Cancer cell of a lineage established for research; now used in many laboratories.

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histone

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Type of protein intimately associated with eukaryotic DNA and largely responsible for organization of eukaryotic chromosomes.

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interphase

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Of a cell cycle, interval between nuclear divisions when a cell increases in mass and roughly doubles the number of its cytoplasmic components. It also duplicates its chromosomes (replicates its DNA) during interphase, but not between meiosis I and II.

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meiosis

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[Gk. meioun, to diminish] Two-stage nuclear division process that halves the chromosome number of a parental germ cell nucleus, to the haploid number. Basis of gamete formation (and meiospore formation).

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metaphase

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Of meiosis I, stage when all pairs of homologous chromosomes have become positioned at the spindle equator. Of mitosis or meiosis II, all the duplicated chromosomes are positioned at the spindle equator.

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mitosis

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[Gk. mitos, thread] Type of nuclear division that maintains the parental chromosome number for daughter cells. The basis of growth in size, tissue repair, and often asexual reproduction for eukaryotes.

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motor protein

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Type of protein (e.g., myosin) attached to microfilaments and microtubules; used in cell movements (e.g., contraction).

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nucleosome

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A stretch of eukaryotic DNA looped twice around a spool of histone molecules; one of many units that give condensed chromosomes their structure.

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prophase

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Of mitosis, a stage when duplicated chromosomes start to condense, microtubules form a spindle, and the nuclear envelope starts to break up. Duplicated pairs of centrioles (if present) are moved to opposite spindle poles.

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reproduction

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Any process by which a parental cell or organism produces offspring. Among eukaryotes, asexual modes (e.g., binary fission, budding, vegetative propagation) and sexual modes. Bacteria use prokaryotic fission.

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sister chromatid

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Of a duplicated chromosome, one of two DNA molecules (and associated proteins) attached at the centromere until they are separated from each other at mitosis or meiosis; each is then a separate chromosome.

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somatic cell

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[Gk. soma-, body] Any body cell that is not a germ cell. (Germ cells are the forerunners of gametes.)

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spindle apparatus

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Dynamic, temporary array of microtubules that moves chromosomes in precise directions during mitosis or meiosis.

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telophase

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Of meiosis I, a stage when one member of each pair of homologous chromosomes has arrived at a spindle pole. Of mitosis and of meiosis II, the stage when chromosomes decondense into threadlike structures and two daughter nuclei form.