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Chapter 12 - The Cell Cycle


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a cell's total hereditary endowment of DNA
Somatic cells
all body cells except for the reproductive cells;
reproductive cells;
sperm cells and egg cells;
DNA-protein complex that forms a long, thin fiber
Sister chromatids
each contains an identical copy of the chromosome's DNA molecule
a region that joins the sister chromatids together to form the chromosome
the division of the nucleus
the divsion of the cytoplasm
a variation of cell division which yields daughter cells that have half as many chromosomes as the parent cell;
occurs only in the gonads
Mitotic (M) phase
includes both mitosis and cytokinesis;
usually the shortest part of the cell cycle
the stage of mitosis in which the single centrosome replicates and separates
the stage of mitosis in which the mitotic spindle begins to form;
chromatin fibers become more coiled and condensed
Mitotic spindle
a structure that consists of fibers of microtubules that begin at the centrosomes and extends to the centromeres of each chromosome
The third stage of cell mitosis in which the two centrosomes are located opposite each other;
the nuclear envelope fragments;
chromosomes continue to condense
a structure of proteins and specific sections of chromosomal DNA at the centromere;
face in opposite directions on the chromosome and attach to the spindle fibers
the centromeres are at opposite poles of the cell;
chromosomes convene on the metaphase plate
stage of mitosis in which the paired centromeres separate and the sister chromatids are pulled to opposite poles of the cell
stage of mitosis in which the nuclear envolope begins to reform in each pole of the cell;
a cleavage furrow forms along what was once called the metaphase plate, cytoplasm begins to divide
Cleavage furrow
a region of the cell that begins as a shallow groove in the cell surface near the old metaphase plate;
cytoplamic side of furrow is a contractile ring of actin and myosin microfilaments that pinch off the cells much like a drawstring
Cell plate
region of cytoplasmic division in plant cells;
vesicles containing cell-wall material migrate to this area and lay down a cell wall
Binary fission
"division in half";
a type of cell division utilized by prokaryotes
Cell-cycle control system
a cyclically operating set of molecules in the cell that both triggers and coordinates key events in the cell cycle
a critical control point where stop and go-ahead signals can regulate the cycle
G0 Phase
a nondividing state that will be entered into if cells reach the restriction point and are not ready to replicate
a protein that gets its name from its cyclically fluctuating conc. in the cell;
attaches to and activates Cdk
Cyclin-dependent kinases (Cdk)
kinases that drive the cell cycle and are present in constant conc., but usually in an inactive form
MPF (maturation promoting factor)
triggers the cells passage past the G2 phase into the M phase;
initiates mitosis by phosphorylating a variety of proteins; also initiates itso own breakdown by hydrolysis
Growth factor
a protein released by certain body cells that stimulates other cells to divide
Density-dependent inhibition of cell division
a phenomenon in which crowded cells stop dividing;
once a cell population reaches a certain density, the amount of required growth factors and nutrientsavailable to each cell becomes insufficient to allow continued cell growth
Anchorage dependence
a phenomenon that most animal cells exhibit in which they must be attached to a substratum in order to divide
the process that converts a normal cell to a cancer cell
a mass of abnormal cells within an otherwise normal tissue
Benign tumor
a tumorous lump in which the cells remain at the original site;
most do not cause serious problems and can be completely removed by surgery
Malignant tumor
a tumor that becomes invasive enough to impair the functions of one or more organs;
can be fatal;
cells of these tumors are often abnormal in many ways, such as abnormal number of chromosomes, deranged metabolism, and loss of function
the spread of cancer cells beyond their original site

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