Learners will examine and sequence the phases of cell division and the functions of mitosis.
After completing this tutorial, you will be able to complete the following:
Mitosis is derived from the Greek word mitos, which means thread. In humans, it is the process where the nucleus of the cell divides, resulting in two sets of identical cells with identical chromosomes, i.e., clones. It is a type of cell division that is on going and produces new cells for growth or repair.
Within the human body, cells are constantly damaged, sloughed off and/or die, especially in the skin, blood and digestive tract. Mitosis occurs to replace these worn out, dead, or damaged cells within the body. However, when damaged cells are repaired, the new cells created must be exact copies in order to retain the normal function of that particular cell.
Thus, in mitosis, when a human cell divides, its 46 chromosomes must be copied or replicated. This process results in two new cells with one copy of each chromosome containing exactly the same genetic information.
Prior to the actual "mitosis" phase, all chromosomes must grow and duplicate. This is often referred to as interphase. Chromosomes spend a majority of their time in interphase. In fact, they spend almost 90% of their time in this phase. Even though interphase is part of the cell cycle, it is not considered to be an actual part of mitosis. This pre-mitosis phase is where the chromosomes duplicate, replicate, grow, and even rest. When the environment is favorable, a cell will proceed into the phase of mitosis. The diagram below shows the stages of the cell cycle, including interphase.
Since mitosis happens so frequently within humans, it has become a smooth, continuous process. To help study it, biologists have divided it into four phases: prophase, metaphase, anaphase and telophase.
The first stage of mitosis is called prophase. Remembering that the chromosomes have already duplicated during the interphase process, the chromosomes now begin to coil and thicken to become pairs. Once paired, they will combine in the middle to look like the letter X, held together in the center by a centromere, which is the point where the chromosomes meet.
Next, a spindle-like, tubular material forms that the chromosomes will eventually attach to. It lengthens and extends to each end or pole.
Lastly, the membrane that surrounds the nucleus fragments and disperses.
In the second mitosis stage, metaphase, the spindle attaches to the centromere in the center of the chromosome. The chromosomes line up and move to the center of the cell.
In the third of the mitosis stages, anaphase, the cell lengthens as it begins the process of division. The spindles shorten, which pulls the chromosome pairs apart and pulls the single chromosomes to opposite ends of the cell. These ends are referred to as the "poles."
In the fourth of the mitosis stages, telophase, the chromosomes reach the poles, and a new nuclear membrane forms around them. Two new cells form, each containing one set of the copied chromosomes. In other words, the cell contains the same number of chromosomes as the original cell.
Lastly, mitosis is accompanied by cytokinesis. Cytokinesis is the process in which the cell membrane is pinched inward at the center, forming two separate cells. These two new cells are each genetically identical to the original cell.
Now that there are two identical body cells, mitosis has completed its task. Cell division, in particular, mitosis, serves an important role in an organism's health and growth. For example, without this process, the human body would not be able to maintain homeostasis (the proper balance in cells). Furthermore, if we did not have homeostasis, disease and death would occur. As a result, it is safe to say that mitosis is a vital process needed to maintain the human body.
|Approximate Time||2 Minutes|
|Pre-requisite Concepts||cells, chromosomes, DNA, nucleus|
|Type of Tutorial||Concept Development|
|Key Vocabulary||ecosystem, food chain, food web|