Start With Bacteria
What is cell division? This process is the recreation of the cell structure using duplication and division of cell DNA, according to Martha
R. Taylor’s book, Student Study Guide for Campbell’s BIOLOGY. Cell division is used to create duplicate offspring in unicellular organisms and for growth, development, and repair in multi-cellular organisms.
Bacteria, also known as prokaryotes, undergo cell division through a process known as binary fission. In this reproduction process a bacteria replicates a single circular DNA molecule attached to the plasma membrane. Once the chromosomes have duplicated, the plasma membrane grows in between the chromosomes to develop a cell wall, resulting in two identical daughter cells. As most prokaryotes are unicellular, binary fission usually serves as the reproductive process for prokaryotic species.
Cell division in eukaryotic cells is more complicated than in prokaryotes and other unicellular organisms. Each eukaryotic species has a different number of chromosomes in each somatic cell. Reproductive cells, also known as gametes, have half the number of chromosomes.
First, the cell duplicates each chromosome, which is a long DNA protein complex, known as chromatin. The replicated chromosomes are connected at a specific region called a centromere. The two identical chromosomes separate during the division of the nucleus in a process called mitosis. A cell’s cytoplasm divides after mitosis in a process called cytokinesis, resulting in two genetically equivalent cells.
When producing reproductive cells a similar cell division process occurs. However, the daughter cells only have half the number of chromosomes of the parent cell. This type of cell division, known as meiosis, is responsible for creating sperm and egg cells. The full number of chromosomes is restored when the egg fertilizes the sperm.
Controlling Cell Division
In order to maintain normal growth and development an organism must be able to control the rate and timing of cell division. Specific regulatory substances called growth factors play an important role in regulating what is cell division. Most cell division is regulated by density-dependent inhibition, which means cell division correlates to diminishing supplies of specific growth factors.
Cancer cells are different than normal cells, because they lack density-dependent inhibition. This means cancer cells continue dividing indefinitely. The body’s immune system usually destroys cancer cells as soon as they are formed. However, the cancer cells sometimes will not be destroyed, allowing them to continue to divide.
When a mass of cancer cells form within a tissue, it is called a tumor. Tumors remaining at their original site are described as benign, while tumors that spread beyond their original site are called malignant. Malignant tumor cell metabolism operates abnormally. These cells also have an unusual number of chromosomes.
Knowledge of cell division is important to understanding the basis of biological life. The medical field is especially interested in increasing knowledge of the cell division process, due to its role in cancer. Medical research has already pinpointed several key genes that are integral in cell division as well as development of breast cancer cellsm, reported Medscape Medical News in an article titled "BRCA2 Plays Unsuspected Role Cell Division." However, further research and study of cell division is needed to better understand how to treat all types of cancer.
Student Study Guide for Campbell's BIOLOGY, by Martha R. Taylor
"BRCA2 Plays Unsuspected Role Cell Division," published in Medscape Medical News; this link is to The Wistar Institute.