centromere
In a duplicated chromosome, the region on each sister chromatid where it is most closely attached to the other chromatid by proteins that bind to the centromeric DNA.
S phase
The synthesis phase of the cell cycle; the portion of interphase during which DNA is replicated.
sister chromatids
Two copies of a duplicated chromosome attached to each other by proteins at the centromere and, sometimes, along the arms. Make up one chromosome when joined.
telophase
The fifth and final stage of mitosis, in which daughter nuclei are forming and cytokinesis has typically begun.
transformation
The conversion of a normal cell into a cell that is able to divide indefinitely in culture, thus behaving like a cancer cell.
interphase
The period in the cell cycle when the cell is not dividing.
malignant tumor
A cancerous tumor containing cells that have significant genetic and cel- lular changes and are capable of invading and surviving in new sites.
metaphase
The third stage of mitosis, in which the spindle is complete and the chromosomes, attached to microtubules at their kinetochores, are all aligned at the center.
metaphase plate
An imaginary structure located at a plane midway between the two poles of a cell in mitosis on which the centromeres of all the duplicated chromosomes are located.
origin of replication
Site where the replication of a DNA molecule begins, consisting of a specific sequence of nucleotides.
prophase
The first stage of mitosis, in which the chromatin condenses into discrete chromosomes visible with a light microscope, the mitotic spindle begins to form, and the nucleolus disappears but the nucleus remains intact.
prometaphase
The second stage of mitosis, in which the nuclear envelope fragments and the spindle microtubules attach to the kinetochores of the chromosomes.
gamete
A haploid reproductive cell, such as an egg or sperm.
genome
The genetic material of an organism or virus; the complete complement of an organism's or virus's genes along with its noncoding nucleic acid sequences.
growth factor
A protein that must be present in the extracellular environment for the growth and normal development of certain types of cells.
G0 phase
A nondividing state occupied by cells that have left the cell cycle, sometimes reversibly.
G1 phase
The first gap, or growth phase, of the cell cycle, consisting of the portion of interphase before DNA synthesis begins.
G2 phase
The second gap, or growth phase, of the cell cycle, consisting of the portion of interphase after DNA synthesis occurs.
cleavage furrow
a shallow groove around the cell in the animal cell surface near the old metaphase plate.
cyclin
A cellular protein that occurs in a cyclically fluctuating concentration and that plays an important role in regulating the cell cycle.
cyclin-dependent kinase (Cdk)
A protein kinase that is active only when attached to a particular cyclin.
cytokinesis
The division of the cytoplasm to form two separate daughter cells immediately after mitosis, meiosis I, or meiosis II.
density-dependent inhibition
The phenomenon observed in normal animal cells that causes them to stop dividing when they come into contact with one another.
centrosome
A structure present in the cytoplasm of animal cells that functions as a microtubule-organizing center and is important during cell division.
checkpoint
A control point in the cell cycle where stop and go-ahead signals can regulate the cycle.
anaphase
The fourth stage of mitosis, in which the chromatids of each chromosome have separated and the daughter chromosomes are moving to the poles of the cell.
aster
A radial array of short microtubules that extends from each centrosome toward the plasma membrane in an animal cell undergoing mitosis.
cell cycle control system
A cyclically operating set of molecules in the eukaryotic cell that both triggers and coordinates key events in the cell cycle.
cell division
The reproduction of cells.
cell cycle
An ordered sequence of events in the life of a cell, from its origin in the division of a parent cell until its own division into two.
chromatin
The complex of DNA and proteins that makes up eukaryotic chromosomes.
chromosome
A cellular structure consisting of one DNA molecule and associated protein molecules.
benign tumor
A mass of abnormal cells with specific genetic and cellular changes such that the cells are not capable of surviving at a new site and generally remain at the site of the origin.
Cleavage
The process of cytokinesis in animal cells, characterized by pinching of the plasma membrane.
Centromere
In a duplicated chromosome, the region on each sister chromatid where it is most closely attached to the other chromatid by proteins.
Metastasis
The spread of cancer cells to locations distant from their original site.
MPF
a protein complex required for a cell to progress from late interphase to mitosis. The active form consists of cyclin and a protein kinase.
Anchorage dependence
The requirement that a cell must be attached to a substratum in order to initiate cell division
cell plate
A membrane-bounded, flattened sac located at the midline of a dividing plant cell, inside which the new cell wall forms during cytokinesis.
somatic cell
A cell in a multicellular organism, except a sperm or egg or their precursors
mitotic spindle
An assemblage of microtubules and associated proteins that is involved in the movement of chromosomes during mitosis.
kinetochore
A structure of proteins attached to the centromere that links each sister chromatid to the mitotic spindle.
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