Cancer is the result of unchecked cell division caused by a breakdown of the mechanisms that regulate the cell cycle. The loss of control begins with a change in the DNA sequence of a gene that codes for one of the regulatory molecules.
Faulty instructions lead to a protein that does not function as it should. Any disruption of the monitoring system can allow other mistakes to be passed on to the daughter cells. Each successive cell division will give rise to daughter cells with even more accumulated damage.
Eventually, all checkpoints become nonfunctional, and rapidly reproducing cells crowd out normal cells, resulting in a tumor or leukemia blood cancer. Skip to main content. Cell Division and Cell Cycle. Search for:. Cancer and the Cell Cycle Learning Objectives: By the end of this section, you will be able to: Describe how cancer is caused by uncontrolled cell growth Understand how proto-oncogenes are normal cell genes that, when mutated, become oncogenes Describe how tumor suppressors function Explain how mutant tumor suppressors cause cancer.
Art Connection Figure 1. Link to Learning Watch this video of how cancer results from errors in the cell cycle:. Additional Self Check Questions Human papillomavirus can cause cervical cancer. E6 activates p53 E6 inactivates p53 E6 mutates p53 E6 binding marks p53 for degradation Outline the steps that lead to a cell becoming cancerous. Explain the difference between a proto-oncogene and a tumor suppressor gene.
List the regulatory mechanisms that might be lost in a cell producing faulty p How does this regulatory outcome benefit a multicellular organism? Answers D. E6 binding marks p53 for degradation. If one of the genes that produces regulator proteins becomes mutated, it produces a malformed, possibly non-functional, cell cycle regulator, increasing the chance that more mutations will be left unrepaired in the cell.
Each subsequent generation of cells sustains more damage. G0 may last for days like the cells in the outer layer of the epidermis , weeks, years, or a lifetime. Image 4 illustrates the processes of cell mitosis and division. Image 4: Cell mitosis and division. Cellular differentiation is the process by which a cell changes its structure so that it can perform a specific function.
Cells can range from poorly differentiated to well-differentiated. The most poorly differentiated cells generally called stem cells are capable of acquiring a range of new functions. Stem cells are important to your overall health. For example, after severe trauma, they provide a pool of cells that can differentiate into specific cell types and repair tissue. Well-differentiated cells are mature, fully developed cells that are ready to carry out their particular function.
A good example of cell differentiation is blood cells. There are 3 major types of blood cells: red blood cells, white blood cells, and platelets. Each has specific characteristics, functions, and life spans, yet all have differentiated from stem cells. Image 5 illustrates the process of cellular differentiation. See the Focus Box below to learn more about the relationship between cell differentiation and cancer. Image 5: Cell differentiation. Focus Box: Cell Differentiation and Cancer.
Poorly differentiated cells are highly proliferative, moderately differentiated cells are moderately proliferative, and well-differentiated cells are either unable to proliferate or proliferate at a very slow rate. Aggressive cancers are often characterized by poorly differentiated cells, while less aggressive cancers tend to contain moderately or well-differentiated cells.
In healthy tissues, the processes of mitosis and differentiation are tightly regulated. This is how the body ensures that only the correct number of cells is produced. The body has 2 methods for controlling the rate of cell proliferation:. If a cell needs to be replaced due to damage, natural apoptosis, or some other reason , it will secrete growth factors that stimulate the cell to either undergo mitosis or differentiate.
Contact inhibition stops cells from proliferating. Under normal conditions, cells that become crowded and begin to touch each other will simply stop growing. Exactly how contact inhibition works is still unknown, however scientists believe that contact between cells triggers the release of growth inhibitory factors. Unlike growth factors, growth inhibitory factors tell cells to stop dividing. In order for the tissues of the body to maintain such precise control over the growth of its cells, it has developed a system of feedback loops that detect and compensate for deviations from the norm.
For every situation controlled by a feedback loop, the body has a set point it recognizes as normal. One example of this is your own body temperature. If your body temperature becomes too warm, a series of physiologic reactions are triggered in an effort reset it. This is an example of a negative feedback loop.
In a positive feedback loop , changes in one direction tend to produce even more change in that same direction, such as the stages of labor that lead to childbirth.
In the case of normal cell proliferation,when the appropriate number of cells has been produced and cells begin to crowd each other growth inhibitory factors trigger a negative feedback mechanism to reduce the rate of cell growth. While positive feedback can occur normally, the production of excess growth factors by cells drives an abnormal positive feedback loop.
Not all abnormally growing cells are cancerous. For example, the term hyperplasia refers to a type of noncancerous growth consisting of rapidly dividing cells, which leads to a larger than usual number of structurally normal cells. Hyperplasia may be a normal tissue response to an irritating stimulus. Calluses that form on your hand when you first learn to swing a tennis racket or a golf club is an example of hyperplastic skin cells.
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