AP BIO CH 12

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.

anchorage dependence

The requirement that to divide, a cell must be attached to the substratum.

aster

A radial array of short microtubules that extends from each centrosome toward the plasma membrane in a cell undergoing mitosis.

benign tumor

A mass of abnormal cells that remains at the site of origin.

binary fission

The type of cell division by which prokaryotes reproduce. Each dividing daughter cell receives a copy of the single parental chromosome.

cell cycle

An ordered sequence of events in the life of a eukaryotic cell, from its origin in the division of a parent cell until its own division into two; composed of the M, G1, S, and G2 phases.

cell cycle control system

A cyclically operating set of molecules in the cell that triggers and coordinates key events in the cell cycle.

cell division

The reproduction of cells.

cell plate

A double membrane across the midline of a dividing plant cell, between which the new cell wall forms during cytokinesis.

centromere

The centralized region joining two sister chromatids.

centrosome

Material present in the cytoplasm of all eukaryotic cells, important during cell division; the microtubule-organizing center.

checkpoint

A critical control point in the cell cycle where stop and go-ahead signals can regulate the cycle.

chromatin

The complex of DNA and proteins that makes up a eukaryotic chromosome. When the cell is not dividing, chromatin exists as a mass of very long, thin fibers that are not visible with a light microscope.

chromosome

A threadlike, gene-carrying structure found in the nucleus. Each chromosome consists of one very long DNA molecule and associated proteins. See chromatin.

cleavage

The process of cytokinesis in animal cells, characterized by pinching of the plasma membrane; specifically, the succession of rapid cell divisions without growth during early embryonic development that converts the zygote into a ball of cells.

cleavage furrow

The first sign of cleavage in an animal cell; a shallow groove in the cell surface near the old metaphase plate.

cyclin

A regulatory protein whose concentration fluctuates cyclically.

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.

density-dependent inhibition

The phenomenon observed in normal animal cells that causes them to stop dividing when they come into contact with one another.

G0 phase

A nondividing state in which a cell has left the cell cycle.

G1 phase

The first growth phase of the cell cycle, consisting of the portion of interphase before DNA synthesis begins.

G2 phase

The second growth phase of the cell cycle, consisting of the portion of interphase after DNA synthesis occurs.

gamete

A haploid cell, such as an egg or sperm. Gametes unite during sexual reproduction to produce a diploid zygote.

genome

The complete complement of an organism's genes; an organism's genetic material.

growth factor

A protein that must be present in the extracellular environment (culture medium or animal body) for the growth and normal development of certain types of cells; a local regulator that acts on nearby cells to stimulate cell proliferation and differentiation.

interphase

The period in the cell cycle when the cell is not dividing. During interphase, cellular metabolic activity is high, chromosomes and organelles are duplicated, and cell size may increase. Interphase accounts for 90% of the cell cycle.

kinetochore

A specialized region on the centromere that links each sister chromatid to the mitotic spindle.

M phase

See mitotic(M) phase.

malignant tumor

A cancerous tumor that is invasive enough to impair the functions of one or more organs.

meiosis

A two-stage type of cell division in sexually reproducing organisms that results in cells with half the chromosome number of the original cell.

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 metaphase plate.

metaphase plate

An imaginary plane during metaphase in which the centromeres of all the duplicated chromosomes are located midway between the two poles.

metastasis

The spread of cancer cells to locations distant from their original site.

mitosis

A process of nuclear division in eukaryotic cells conventionally divided into five stages: prophase, prometaphase, metaphase, anaphase, and telophase. Mitosis conserves chromosome number by equally allocating replicated chromosomes to each of the daughter nuclei.

mitotic (M) phase

The phase of the cell cycle that includes mitosis and cytokinesis.

mitotic spindle

An assemblage of microtubules and associated proteins that is involved in the movements of chromosomes during mitosis.

MPF

Maturation-promoting factor (M-phase-promoting factor); a protein complex required for a cell to progress from late interphase to mitosis. The active form consists of cyclin and a protein kinase.

origin of replication

Site where the replication of a DNA molecule begins.

prometaphase

The second stage of mitosis, in which discrete chromosomes consisting of identical sister chromatids appear, the nuclear envelope fragments, and the spindle microtubules attach to the kinetochores of the chromosomes.

prophase

The first stage of mitosis, in which the chromatin is condensing and the mitotic spindle begins to form, but the nucleolus and nucleus are still intact.

S phase

The synthesis phase of the cell cycle; the portion of interphase during which DNA is replicated.

sister chromatids

Replicated forms of a chromosome joined together by the centromere and eventually separated during mitosis or meiosis II.

somatic cell

Any cell in a multicellular organism except a sperm or egg cell.

telophase

The fifth and final stage of mitosis, in which daughter nuclei are forming and cytokinesis has typically begun.

transformation

(1) The conversion of a normal animal cell to a cancerous cell. (2) A change in genotype and phenotype due to the assimilation of external DNA by a cell.