Intro To Biology

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binary fission

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asexual reproduction by division of one cell or body into two equal or nearly equal parts

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septum

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a wall between two cavities

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septation

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in prokaryotic cell division, the formation of a septum where new cell membrane and cell wall is formed to separate two daughter cells

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mitosis

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somatic cell division; nuclear division in which the duplicated chromosomes separate to form two genetically identical daughter nuclei

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heterochromatin

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the portion of a eukaryotic chromosome that is not transcribed into RNA; remains condensed in interphase and stain intensely in histological preparations.

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euchromatin

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that portion of a eukaryotic chromosome that is transcribed into mRNA; contains active genes that are not tightly condensed during interphase

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nucleosome

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a complex consisting of a DNA duplex wound around a core of eight histone proteins

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karyotype

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the morphology of the chromosomes of an organism as viewed with a light microscope

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haploid

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having only one set of chromosomes (n), in contract to diploid (2n)

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diploid

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having two sets of chromosomes

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homologous

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refers to a pair of the same kind of chromosome in a diploid cel

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homologue

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one of a pair of chromosomes of the same kind located in a diploid cell; one copy of each pair of homologues comes from each gamete that formed the zygote

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cohesin

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a protein complex that holds sister chromatids together during cell division. the loss of cohesins at the centromere allow the anaphase movement of chromosomes.

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chromatid

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one of the two daughter strands of a duplicated chromosome that is joined by a single centromere

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G0 phase

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the stage of the cell cycle occupied by cells that are not actively dividing

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centromere

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a visible point of constriction on a chromosome that contains repeated DNA sequences that bind specific proteins. These proteins make up the kinetochore to which microtubules attach during cell division

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kinetochore

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disk-shaped protein structure within the centromere to which the spindle fibers attach during mitosis or meiosis

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tubulin

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globular protein subunit forming the hollow cylinder of microtubules

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p53 gene

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the gene that produces the p53 protein that monitors DNA integrity and halts cell division if DNA damage is detected

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cancer

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the unrestrained growth and division of cells; it results from a failure of cell division control

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prophase

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the phase of cell division that begins when the condensed chromosomes become visible and ends when the nuclear envelope breaks down. the assembly of the spindle takes place during this phase

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aster

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in animal cell mitosis, a radial array of microtubules extending from the centrioles toward the plasma membrane, possibly serving to brace the centrioles for retraction of the spindle

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spindle

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the structure composed of microtubules radiating from the poles of dividing cell that will ultimately guide the sister chromatids to the two poles

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histone protein

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any of eight proteins with an overall positive charge that associate in a complex. the DNA duplex coils around a core of eight histone proteins, held by its negatively charged phosphate groups, forming a nucleosome

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condensin

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a protein complex involved in condensation of chromosomes during mitosis and meiosis

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G1 phase

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the phase of the cell cycle after cytokinesis and before DNA replication called the first "gap" phase. this phase is the primary growth phase of a cell

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interphase

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the period between two mitotic or meiotic divisions in which a cell grows and its DNA replicates

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cytokinesis

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division of the cytoplasm of a cell after nuclear division

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G2 phase

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the phase of the cell cycle between DNA replication and mitosis called the second "gap" phase. during this phase, the cell prepares for mitosis

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prometaphase

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the transitional phase between prophase and metaphase during which the spindle attaches to the kinetochores of sister chromatids

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metaphase

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the stage of mitosis or meiosis during which microtubules become organized into a spindle and the chromosomes come to lie in the spindle's equatorial plane

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anaphase

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in mitosis and meiosis II, the stage initiated by separation of sister chromatids, during which the daughter chromosomes move to opposite poles of the cell; in meiosis I, marked by separation of replicated homologous chromosomes

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telophase

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the phase of cell division during which the spindle breaks down, the nuclear envelope of each daughter cell forms, and the chromosomes uncoil and become diffuse

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cleavage furrow

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the constriction that forms during cytokinesis in animal cells that is responsible for dividing the cell into two daughter cells

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cell plate

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the structure that forms at the equator of the spindle during early telophase in the dividing cells of plants and a few green algae

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cyclin

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any of a number of proteins that are produced in synchrony with the cell cycle and combine with certain protein kinases, the cyclin-dependent kinases, at certain points during cell division

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cyclin-dependent kinase

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any of a group of protein kinase enzymes that control progress through the cell cycle. these enzymes are only active when complexed with cyclin

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G1/S checkpoint

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the primary control point at which a cell "decides" whether or not to divide.

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G2/M checkpoint

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the second cell-division control point, at which division can be delayed if DNA has not been properly replicated or is damaged

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M phase-promoting factor (MPF)

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a CDK enzyme active at the G2/M checkpoint

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spindle checkpoint

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the third cell-division checkpoint, at which all chromosomes must be attached to a spindle. passage through this checkpoint commits the cell to anaphase

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anaphase-promoting complex (APC)

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a protein complex that triggers anaphase; it initiates a series of reactions that ultimately degrades cohesin, the protein complex that holds the sister chromatids together. the sister chromatids are then released and move toward opposite poles in the cell

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tumor-suppressor gene

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a gene that normally functions to inhibit cell division; mutated forms can lead to the unrestrained cell division of cancer, but only when both copies of the gene are mutant

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oncogene

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a mutant form of a growth-regulating gene that is inappropriately "on", causing unrestrained cell growth and division

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proto-oncogene

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a normal cellular gene that can act as an oncogene when mutated

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retinoblastoma susceptibility gene

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a gene that, when mutated, predisposes individuals to a rare form of cancer of the retina; one of the first tumor-suppressor genes discovered