Mitosis is the process by which a eukaryotic cell separates the chromosomes in its cell nucleus into two identical sets, in two separate nuclei. It is generally followed immediately by cytokinesis, which divides the nuclei, cytoplasm, organelles and cell membrane into two cells containing roughly equal shares of these cellular components.
[During telophase and cytokinesis,] the chromosomes have moved close to the spindle pole regions, and the spindle midzone begins to clear. In this middle region of the spindle, a thin line of vesicles begins to accumulate. The vesicle aggregation event is a harbinger to the assembly of a new cell wall that will be positioned midway along the length of the original cell. It will form the boundary between the newly separating daughter cells. Vesicles movement and aggregation in the spindle midzone is facilitated by a microtubule network known as a phragmoplast. This basket shaped structure forms in late anaphase or early telophase and disassembles about the time that the vesicles begin to coalesce.
Mitosis is the process that facilitates the equal partitioning of replicated chromosomes into two identical groups. Before partitioning can occur, the chromosomes must become aligned so that the separation process can occur in an orderly fashion. The alignment of replicated chromosomes and their separation into two groups is a process that can be observed in virtually all eukaryotic cells.
One interesting offshoot of the study of mitosis is tissue culture. In tissue culture, the cells to be studied are removed from the organism’s body and grown on a sterile, artificial medium. When grown in this manner, typically normal cells grow one layer thick on the surface of the sterile medium and will undergo only 20 to 50 mitotic divisions then cease to be able to reproduce. Also, typically, when all cells are touching neighbors all around, they stop dividing. This phenomenon is known as contact inhibition.
Cells can divide, and in unicellular organisms, this makes more organisms. In multicellular organisms, cell division is used for growth, development, and repair of the organism. Cell division is controlled by DNA, but exact copies of the DNA must be given to the daughter cells (note use of “mother” and “daughter”). Bacteria reproduce by a simple process called binary fission. They have one chromosome which is attached to the cell membrane. This chromosome replicates, then the two copies are pulled apart as the cell grows. Eventually the cell pinches in two to make two cells. Eukaryotes do mitosis. In mitosis, each daughter cell gets about half of the cytoplasm from the mother cell and one set or copy of the DNA.
[During prophase,] the chromosomes coil. The nuclear membrane disintegrates. Spindle fibers (microtubles) form.
Mitosis produces two daughter cells that are identical to the parent cell. If the parent cell is haploid (N), then the daughter cells will be haploid. If the parent cell is diploid, the daughter cells will also be diploid.
Although some amoebas haven't been caught having sex, the authors' taxonomic work suggests amoebic ancestors did do it—just like the common ancestor that led to all modern eukaryotes. It's not certain what pushed some amoebas into celibacy, but they may have evolved in stable environments that didn't require the energy costs of, or genetic advantages conferred by sex. After dropping the ability to sexually shuffle their genes, perhaps they simply got by reproduction via mitosis.
Amoebas are single-celled blobs that house their DNA in nuclei, just like all of their eukaryotic relatives (humans included). Although some amoebas presumably cannot have sex and divide by mitosis, others are among the eukaryotes that can have sex—a process that can most simply be defined as ripping a genome in half and later recombining it.
Eukaryotic chromosomes occur in the cell in greater numbers than prokaryotic chromosomes. The condensed replicated chromosomes have several points of interest. The kinetochore is the point where microtubules of the spindle apparatus attach. Replicated chromosomes consist of two molecules of DNA (along with their associated histone proteins) known as chromatids. The area where both chromatids are in contact with each other is known as the centromere the kinetochores are on the outer sides of the centromere.
Mitosis is the process of forming (generally) identical daughter cells by replicating and dividing the original chromosomes, in effect making a cellular xerox... Mitosis deals only with the segregation of the chromosomes and organelles into daughter cells.
A new version of the Citelighter Toolbar is available.
We have updated some of the features and functions of Citelighter to improve the experience. The version of the Citelighter Toolbar that you have is older and might not function correctly.
You can get the newest version by pressing the button below.