The following sections of this BookRags Literature Study Guide is offprint from Gale's For Students Series: Presenting Analysis, Context, and Criticism on Commonly Studied Works: Introduction, Author Biography, Plot Summary, Characters, Themes, Style, Historical Context, Critical Overview, Criticism and Critical Essays, Media Adaptations, Topics for Further Study, Compare & Contrast, What Do I Read Next?, For Further Study, and Sources.
(c)1998-2002; (c)2002 by Gale. Gale is an imprint of The Gale Group, Inc., a division of Thomson Learning, Inc. Gale and Design and Thomson Learning are trademarks used herein under license.
The following sections, if they exist, are offprint from Beacham's Encyclopedia of Popular Fiction: "Social Concerns", "Thematic Overview", "Techniques", "Literary Precedents", "Key Questions", "Related Titles", "Adaptations", "Related Web Sites". (c)1994-2005, by Walton Beacham.
The following sections, if they exist, are offprint from Beacham's Guide to Literature for Young Adults: "About the Author", "Overview", "Setting", "Literary Qualities", "Social Sensitivity", "Topics for Discussion", "Ideas for Reports and Papers". (c)1994-2005, by Walton Beacham.
All other sections in this Literature Study Guide are owned and copyrighted by BookRags, Inc.
Oncogenes are segments of genetic material (DNA) that are able to induce cancer in animals. They were first discovered in retroviruses (viruses containing the enzyme, reverse transcriptase, and RNA rather than DNA) that were found to cause cancer in many animals. Studies of humans led to the discovery of related genes called proto-oncogenes, which do not normally cause cancer, but have similar DNA sequences. Proto-oncogenes have since been found to play an important role in the growth, differentiation and proliferation of normal cells. They may be converted into oncogenes by several mechanisms, the simplest of which is a point mutation that alters a single nucleotide base pair. They may also be converted to cancer-causing agents by chromosomal rearrangements that remove them from controlling elements present in unaltered chromosomes. The altered oncogenes can no longer function as control agents do, and the result is uncontrolled cell growth resulting in a cancerous tumor. About 60 oncogenes have been discovered in humans. They have been linked to malignancies of the breast, lung, colon, and pancreas.
The nomenclature in this field is somewhat confusing. Oncogenes were discovered first, and their name was derived from the Greek onkos, meaning bulk, or mass, because of their ability to cause tumor growth. Proto-oncogenes were named for their potential to become agents of malignant growth, and as a result, their important role as regulators of normal cellular activity is not properly emphasized.