Chapter 12 - The Cell Cycle Flashcards
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. The eukaryotic cell cycle is composed of interphase (including G1, S, and G2 subphases) and M phase (including mitosis and cytokinesis).
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.
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. (A bacterial chromosome usually consists of a single circular DNA molecule and associated proteins. It is found in the nucleoid region, which is not membrane bounded.) <em>See also</em> chromatin.
chromatin
The complex of DNA and proteins that makes up eukaryotic chromosomes. 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.
somatic cell
Any cell in a multicellular organism except a sperm or egg or their precursors.
gamete
A haploid reproductive cell, such as an egg or sperm. Gametes unite during sexual reproduction to produce a diploid zygote.
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. Chromatids are eventually separated during mitosis or meiosis II.
centromere
In a duplicated chromosome, the region in each sister chromatid where they are most closely attached to each other by proteins that bind to specific DNA sequences; this close attachment causes a constriction in the condensed chromosome. (An uncondensed, unduplicated chromosome has a single centromere, identified by its DNA sequence.)
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 allocating replicated chromosomes equally to each of the daughter nuclei.
cytokinesis
The division of the cytoplasm to form two separate daughter cells immediately after mitosis, meiosis I, or meiosis II.
mitotic (M) phase
The phase of the cell cycle that includes mitosis and cytokinesis.
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 often accounts for about 90% of 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.
S phase
The synthesis phase of the cell cycle; the portion of interphase during which DNA is replicated.
G2 phase
The second gap, or growth phase, of the cell cycle, consisting of the portion of interphase after DNA synthesis occurs.
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.
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.
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.
telophase
The fifth and final stage of mitosis, in which the daughter nuclei are forming and cytokinesis has typically begun.
mitotic spindle
An assemblage of microtubules and associated proteins that is involved in the movement of chromosomes during mitosis.
centrosome
A structure present in the cytoplasm of animal cells that functions as a microtubule-organizing center and is important during cell division. A centrosome has two centrioles.
aster
A radial array of short microtubules that extends from each centrosome toward the plasma membrane in an animal cell undergoing mitosis.
kinetochore
A structure of proteins attached to the centromere that links each sister chromatid to the mitotic spindle.
metaphase plate
An imaginary structure located at a plane midway between the two poles of a cell in metaphase on which the centromeres of all the duplicated chromoes are located.
cleavage
(1) The process of cytokinesis in animal cells, characterized by pinching of the plasma membrane. (2) The succession of rapid cell divisions without significant growth during early embryonic development that converts the zygote into a ball of cells.
cleavage furrow
The first sign of cleavage in an animal [or human] cell; a shallow groove around the cell in the cell surface near the old metaphase plate.
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.
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.
origin of replication
Site where the replication of a DNA molecule begins, consisting of a specific sequence of nucleotides.
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.
checkpoint
A control point in the cell cycle where stop and go-ahead signals can regulate the cycle.
G0 phase
A nondividing state occupied by cells that have left the cell cycle, sometimes reversibly.
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.
MPF
Maturation-promoting factor (or 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.
growth factor
(1) A protein that must be present in the extracellular environment (culture medium or animal [or human] body) for the growth and normal development of certain types of cells.
density-dependent inhibition
The phenomenon observed in normal animal [and human] cells that causes them to stop dividing when they come into contact with one another.
anchorage dependence
The requirement that a cell must be attached to a substratum in order to initiate cell division.
transformation
(1) The conversion of a normal animal [or human] cell to a cancerous cell. (2) A change in genotype and phenotype due to the assimilation of external DNA by a cell. When the external DNA is from a member of a different species, transformation results in horizontal gene transfer.
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 tumor’s origin.
malignant tumor
A cancerous tumor containing cells that have significant genetic and cellular changes and are capable of invading and surviving in new sites. Malignant tumors can impair the functions of one or more organs.
metastasis
The spread of cancer cells to locations distant from their original site.
