Question | Answer |
Actin | A globular protein that links into chains, two of which twist helically about each other, forming microfilaments in muscle and other kinds of cells. |
anaphase | 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. |
binary fission | A method of asexual reproduction by “division in half.” In prokaryotes, binary fission does not involve mitosis; but in single-celled eukaryotes that undergo binary fission, mitosis is part of the process. |
cell cycle | ordered sequence of events in the life of a eukaryotic cell, composed of interphase (G1, S, & G2) and M phase (mitosis & cytokinesis) |
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 plate | A double membrane across the midline of a dividing plant cell, between which the new cell wall forms during cytokinesis. |
centromere | The specialized region of the chromosome where two sister chromatids are most closely attached. |
centrosome | Structure present in the cytoplasm of animal cells, important during cell division; functions as a microtubule-organizing center. A centrosome has two centrioles. |
checkpoint | A 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 in its dispersed form, as a mass of very long, thin fibers that are not visible with a light microscope. |
chromosome | A cellular structure carrying genetic material, found in the nucleus of eukaryotic cells. Each chromosome consists of one very long DNA molecule and associated proteins. |
cleavage | The process of cytokinesis in animal cells, characterized by pinching of the plasma membrane. |
cleavage furrow | The first sign of cleavage in an animal cell; a shallow groove in the cell surface near the old metaphase plate. |
cytokinesis | The division of the cytoplasm to form two separate daughter cells immediately after mitosis, meiosis I, or meiosis II. |
Down syndrome | A human genetic disease caused by the presence of an extra chromosome 21; characterized by mental retardation and heart and respiratory defects. |
G0 phase | A nondividing state occupied by cells that have left the cell cycle. |
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. |
gamete | A haploid reproductive cell, such as an egg or sperm. They unite during sexual reproduction to produce a diploid zygote. |
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. |
interphase | The period in the cell cycle when the cell is not dividing. Cellular metabolic activity is high, chromosomes and organelles are duplicated, and cell size may increase. Accounts for 90% of cell cycle. |
kinetochore | A structure of proteins attached to the centromere that links each sister chromatid to the mitotic spindle. |
metaphase | the spindle is complete and the chromosomes, attached to microtubules at their kinetochores, are all aligned at the equatorial plate. |
metaphase plate | An imaginary plane midway between the two poles of a cell in metaphase on which the centromeres of all the duplicated chromosomes are located. |
mitosis | nuclear division in eukaryotic cells conventionally divided into five stages: prophase, prometaphase, metaphase, anaphase, and telophase. Mitosis conserves chromosome number |
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. |
origin of replication | Site where the replication of a DNA molecule begins, consisting of a specific sequence of nucleotides. |
prometaphase | discrete chromosomes consisting of identical sister chromatids appear, the nuclear envelope fragments, and the spindle microtubules attach to the kinetochores of the chromosomes. |
prophase | chromatin condenses, the mitotic spindle begins to form, and the nucleolus disappears, but the nucleus remains intact. |
S phase | 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. While joined, two sister chromatids make up one chromosome |
somatic cell | Any cell in a multicellular organism except a sperm or egg. |
telophase | final stage of mitosis, in which daughter nuclei are forming and cytokinesis has typically begun. |