To guarantee that every cell in the body has the same genetic information, cell reproduction occurs through the process called mitosis.
Cell reproduction means producing offspring that may or may not be exact copies of their parents. It is a part of a life cycle, which is a series of events wherein individuals grow, develop, and reproduce according to a program of instructions encoded in DNA, which they inherit from their parents. When cells divide, each daughter cell receives a complete copy of DNA and enough cytoplasmic machinery to start up its own operation. DNA contains the blueprints for making different proteins. Some of the proteins serve as structural materials. Others serve as enzymes for reactions by which carbohydrates, lipids and other substances are formed. Proteins, carbohydrates and lipids are used in building the membranes, organelles and other parts of each new cell. In all cells and some cells of the reproductive system cell division consists of mitosis and cytokinesis.
What is mitosis?
Mitosis is the division of cell nucleus, which results in the formation of two daughter nuclei with exactly the same genes as the mother nucleus. When the nucleus divides, each daughter cell ends up with exactly the same genetic information as the original mother and the original fertilized egg from which it came. The life cycle of a cell extends from the time that the cell is formed until its division has been completed. Mitosis is only a small part of the cycle; it lasts only for a few minutes or an hour or more. Typically, it takes for 2 hours. Mitosis provides the new cells for body growth in youth and vital to repair body tissues all through life. Disorganized mitosis is the basis for tumors and cancers. The cycle has two major periods: interphase and cell division. Interphase is the period in which the cell grows and carries on its usual metabolic activities. Cell division or mitotic phase is the period in which the cell reproduces itself. Mitosis is the same in all animal cells. Mitosis typically lasts about 2 hours, however It could take place from 5 minutes to several hours to complete depending on the type of tissue.
The chromosomes are in an extended form and seen as chromatin in the electron microscope and the nucleus is visible.
Stages of Mitosis
These are the stages of Mitosis:
The chromosomes are seen to consist of two chromatids joined by a centromere. The centrioles move apart toward opposite poles of the cell. Spindle fibers are produced and extend from each centrosome. The nuclear membrane starts to disappear and the nucleolus is no longer visible.
The chromosomes are lined up at the equator of the cell. The spindle fibers from each centriole are attached to the centromeres of the chromosomes and the nuclear membrane has disappeared.
During anaphase, sister chromatids of each chromosomes are separated. Microtubule-based mechanisms move the two chromatids of each pair to opposite poles.
Telophase is essentially prophase in reverse. Microfilaments begin to constrict at equatorial plane. New nuclear membranes start forming. The nucleus reappears. Cell division is nearly complete.
Images of the Stages of Mitosis
Cytokinesis or cytoplasmic division
Cytokinesis is the cytoplasmic division accompanying or following nuclear divisions. The onset of cytokines is marked by the appearance of scattered deposits of materials around microtubules at the spindle equator. The deposits then accumulate until they form a distinct layer across the cell. Then there is the appearance of a shallow ring-like depression at the plasma membrane called cleavage furrow. At the cleavage furrow, a ring of contractile microfilaments attached to the plasma membrane pulls the membrane inward eventually dividing the cytoplasm into two. Thus at the end of cell division, two identical daughter cells exist.
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Questions for Study and Review
1. Define and contrast mitosis and cytokinesis.
2. Name the process of cell division. What happens to the chromosomes during cell division? What about to the organelles?
Ivyespanola on December 20, 2015:
Ivory Española BSBA 3(1-4)
Cytokinesis is an eventual outcome of mitosis
when mitosis or cell division happens when all the DNA and proteins are already prepared the cytoplasm divides (cytokinesis) leading to 2 new cells and cytokinesis happens in certain phases of mitosis like anaphase and telophase.
The mitosis division process has several steps or phases of the cell cycle: interphase, prophase, prometaphase, metaphase, anaphase, telophase, and cytokinesis—to successfully make the new diploid cells. When a cell divides during mitosis, some organelles are divided between the two daughter cells.
Mariella Dela Paz on December 20, 2015:
Cell division depends on two complementary events- the replication of the DNA molecules taht make up the basic genetic material of all cells, and orderly separation of the products of this replication. In simple prokaryotes, where only a single unit of DNA exist, these two events are intimately coupled with an inward growth of the cell membrane.
In eukaryotes, the process is more complex. Here, the DNA is combined with histone protein and is separated into two or more discrete chromosomes that are enclosed in a distict nuclear membrane. Division of the nucleus thus precedes divison of the cytoplasm, and both are necessary for cell division. During nuclear division, the behavior of the individual chromosomes must be coordinated, both spatially and temporary. This is achieved by the assembly of two temporary sets of microtubules that together form a spindle. The products of chromosome replication are oriented and move within this system as a result of the activity of specialized chromosome regions, called kinetochores or centromeres.