What Is Mitosis?
CLASS NOTES from Science Prof Online
Why Do Cells Divide?
You grew from a zygote, or fertilized egg (the fusion of two cells: an ovum and a sperm) into an organism with trillions of specialized cells. Mitosis is the process that enabled you to grow and develop after that fateful meeting of egg and sperm became ‘you’. That is the human life cycle.
Cells must divide in order for an organism to grow and develop, but cell division is also required for
Article Summary: In order for organisms to grow, develop and maintain life, cells must divide. Cellular division involves the basic stages of interphase, nuclear division and cytokinesis. Here's a summary.
Mitotic Cell Division of Eukaryotes
Portions of this article originally appeared on Suite101 online magazine.
Page last updated: 4/2014
You have free access to a large collection of materials used in a college-level introductory microbiology course. The Virtual Microbiology Classroom provides a wide range of free educational resources including PowerPoint Lectures, Study Guides, Review Questions and Practice Test Questions.
Interphase consists of 3 stages:
- G1 phase: cell grows in size
- S phase: DNA is copied (replicated) in preparation for cell division
- G2 phase: cell competes preparations for division
Mitotic Cell Division consists of 2 major processes:
- Mitosis: Nuclear division (separation of the duplicated genetic material)
- Cytokinesis: cytoplasmic division (cell divides into two daughter cells)
There are two major phases to the cell cycle:
During interphase, the cell is not dividing, but is going about the everyday business of being a cell. The DNA is constantly being read and the genetic instructions translated into polypeptides, so the DNA exists in long strands called chromatin.
Mitosis has 4 basic sub-phases:
- Prophase – Chromatin strands condense into chromosomes. The chromosome consists of duplicated, condensed strands of DNA, each copy called a sister chromatid.
- Metaphase – Duplicated chromosomes align at the cell’s equatorial plane.
- Anaphase – Sister chromatids separate and migrate to opposite poles of the cell.
- Telophase – Chromosomes revert to their extended state (chromatin). Nuclear envelope reforms around each of the 2 groups of genetic material. Cytokinesis begins.
The cytoplasm and its contents are then divided by a process called cytokinesis. In animal cells a cleavage furrow forms that essentially pinches the cell in two. Plant cells build a cell plate between the genomes of the two newly forming cells.
HINT! How to Remember the Stages of the Cell Cycle
Students trying to remember the main stages of the cell cycle often use the following acronym "I-PMAT", with the slightly gross sentence "I peed on the MAT." This helps them remember interphase, prophase, metaphase, anaphase and telophase in the proper order.
Visual & Animated Resources to Help Students Understand Mitosis
- Mitosis animated tutorial and quiz from Sumanas Inc
- Campbell, N. A. & Reece J. B. (2005) Biology, seventh edition. Pearson Education Inc.
- Campbell, N. A., Reece J. B. & Simon, E. (2004) Essential Biology with Physiology, Pearson Education Inc.
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tissue repair, maintenance, cell turnover and replacement.
Many tissues in your body are composed of cells that have a high turn-over rate. Think of your skin. The epidermis, or top layer, is composed of dead cells that are constantly being sloughed off and replaced from below by cells of the dermis (the living cells in the layer of skin below the epidermis). If cells of the dermis were not constantly dividing to replace dead cells, your skin would eventually wear out.
This is also true of the mucus membranes of your body; the moist areas of the GI tract and urogenital tract that are the interface between your internal systems with the outside world.
Some cell types of your body, once formed, do not undergo much division, like neurons (nerve cells), for example. Others, like the skin cells mentioned above, undergo a high rate of mitosis. Most other cell types are in between, with a moderate rate of cell division.
Eukaryotic Cell Cycle
During the cell cycle, somatic cells (non-reproductive cells) of eukaryotic organisms grow and divide. It is the process of a single cell (parent cell) splitting into two identical ‘daughter cells’. The daughter cells are clones of the parent, and have the same number of chromosomes as the parent cell.