Discovery Science: Earth – Evolution – Mitosis: Replication Of Cells

Earth Science: Biology – Evolution – Mitosis: Replication Of Cells

Multicellular organisms consist of a very large number of cells, but they always grow from one single cell, normally a fertilized egg.

Before eukaryotic cells can replicate, their nuclei must be divided. This is what mitosis does. The genetic in- formation of the cell is distributed evenly between the daughter cells so that, once mitosis is completed, each new cell has the same set of chromosomes as the original cell. This process may be divided into multiple phases.

During prophase, chromosomes coil up to prepare for transportation and division. The nuclear membrane begins to disintegrate. In metaphase, the chromosomes are already so condensed that they are visible in a light microscope. Tubular protein filaments (microtubules) form a spindle and the chromosomes align along the metaphase, or equatorial

During anaphase, the centromeres (the points where chromosomes attach to the spindle fibers) segregate and the spindles pull the chromatids of each chromosome toward opposite poles of the cell. Each pole gets one full set of chromatids. During the telophase, the spindle disintegrates, a new nuclear membrane forms around each set of chromatids, and the cytoplasm divides (cytokinesis).

New cell membranes form (as do cell walls in plants) and the chromosomes reassume their functional shape. The time between nuclear or cellular divisions (interphase) allows cells to grow and reach the size of their parent cells, as well as to form organelles. Furthermore, the chromatids double (identical replication) and the nucleus begins to regulate the metabolic activities of the cell, such as protein biosynthesis, before the process of replication begins all over again.


Cytostatic agents are used in cancer treatment to slow down the growth and division of tumor cells. Antimitotics—drugs that inhibit mitosis—are cytostatic agents that bind to the micro- tubular proteins (tubulin), thus temporarily blocking cell division.

The use of antimitotic agents requires careful consideration: healthy cells will also be affected to some extent.


Human bodies consist of about ten trillion (10^13) cells, all of which originate from a single maternal ovum that has developed into an organism by continuous cell division. In addition, the gastrointestinal tract contains about 100 trillion (10^14) cells of microorganisms, and there are another trillion (10^12) bacteria on the skin.

Despite their numbers, these extra cells add only 3.5 ounces (100 g) in weight, due to the large difference in size between the eukaryotic cells of the human body and prokaryotic bacterial cells