Proto-oncogenes and Oncogenes: How Different Are They?

According to the American Cancer Soceity 2008 study, about one in every three women and one in every two men, are likely to have cancer in their lifetime. Cancer is often a devastating disease and many scientists continue to discover the mechanisms of its development, and search for ways to cure it. Studies have shown that genes often play a role in normal body growth and in cancer formation. Examples of these genes are the proto-oncogene and oncogene, respectively. The difference between proto-oncogene and oncogene generally lie in their functions inside the body.


Proto-oncogenes are usually responsible in making proteins which are important in stimulating division of cells, in stopping apoptosis or cell death, and in controlling cell differentiation. These processes are often necessary in the growth and maintenance of body organs and tissues. During embryogenesis, the action of these proto-oncogenes are mostly increased since tissues and organs are continually developing. As their functions are completed, some of these activities are often turned off.

There are several classifications of proto-oncogene groups, and these classifications are generally based on their function inside the cell. Examples of proto-oncogenes are receptor tyrosine kinases, growth factors, and membrane associated G-proteins, among many others.

From cell growth, through differentiation and during proliferation, these different kinds of proto-oncogenes are usually involved in the process. When these proto-oncogenes undergo mutations, however, they become oncogenes, which are capable of turning normal cells into cancer cells. Mutations are permanent alterations or changes that occur in the sequence of DNA in a given gene, often resulting in the production of a protein that functions differently, like increasing its activity or performance.


Oncogenes are proto-oncogenes that experienced mutation through several possible means. These include deletion and insertion mutations, increased transcription, point mutations, and gene amplification, among others. Viruses can also cause transformation of the proto-oncogene into an oncogene.

When these mutations occur, the result is often an increased activity in the affected proto-oncogenes. Cells often divide continually, causing it to increase in numbers, and in the growth of tumor size. There is also increased inhibition of apoptosis that regulate the death of cells naturally. When this happens, cells which are supposed to die, continue to stay in the body. These mechanisms are typical of how cancer develops inside the body.

Reactivation of proto-oncogenes that were turned off when their functions were completed, can also cause cancer formation later in life. And those that continue to perform increased activities than necessary may also contribute to the growth of cancer.

The Difference Between Proto-Oncogene and Oncogene Classes

Of the two gene classes, the proto-oncogenes are necessary for the proper development of a healthy body. Oncogenes, on the other hand, often promote negative effects inside the cells, thus leading to cancer formation.


Scitable: Proto-oncogenes to Oncogenes to Cancer Introduction to Cancer