Cancer

Controlled vs Uncontrolled Cell Growth

Controlled Cell Growth

Why do cells need controls on their rate of growth and division? What would happen if cells continued to divide without control? In order to properly function, cells need to be regulated from their internal and external environment.

Before cells divide, each chromosome must be duplicated and then attach to a spindle fiber. If these events in the cell cycle do not occur properly, the daughter cell will not have all the genetic information required to function. Therefore, cells must have an internal regulator to ensure these events occur accurately. These internal regulators provide quality control for the cell. Special proteins classified as cyclins are involved with regulating the cell cycle. Proteins that control internal events are called internal regulators.

Proteins that respond to factors are called external regulators. External factors may be physical or chemical. When cells touch each other through physical contact, their cell cycle is affected. Proteins on the surface of cells bind to each other and cause the cell cycle to slow down by releasing signals that block cell growth. In contrast, proteins that cause cells to speed up cell division are called growth factors.

Growth factors are chemical signals that direct cells to grow. For example, new cells are needed to replace cells lost or damaged due to an injury. Growth factors stimulate cells at the site of the injury, causing them to divide rapidly. This action starts the healing process. Proteins that function as hormones are other examples of growth factors. Human growth hormone is an example of a growth facor that stimulates bone cells to grow and divide.

Uncontrolled Cell Growth

If cells are not controlled properly through internal and external regulators, cells will divide continuously. An example of uncontrolled growth is cancer. This uncontrolled growth causes cells to form masses called tumors. Tumor cells that break away can form new masses. This is called malignancy. If cancer cells continue to grow and spread, they will eventually kill the organism.

Cancer causes harm to an organism because the cancer cells use up nutrients and oxygen without providing a specialized function for the organism. The added space a tumor occupies creates stress on other cells and may cause them to stop working properly.

Cancer is caused by a variety of factors that include smoking, exposure to excessive radiation from the sun, pollution, and some viruses. Agents that cause cancer are called carcinogens. Carcinogens affect normal cells by causing the genetic material to change or mutate. These mutations affect the proteins that regulate the cell cycle. Some of these mutations prevent the cells from being able to respond to external regulators that slow down or stop cell division when contacting other cells. Other mutations affect internal regulators that make sure cell division occurs properly.