Cancer occurs when a cell divides when it should not. This straying from normal cell behavior is caused by mutations in three general types of genes: oncogenes, tumor suppressor genes, and DNA repair genes. These mutations can either change the amount of protein that's made (from none to too much) or the way the protein functions. Highly malignant tumors often contain mutations in all three types of genes.

Oncogenes code for proteins which – if active –make a cell divide when it should not. Their normal counterparts are called "proto-oncogenes" and are involved in regulating cell growth. Oncogenes get activated when mutations occur that increase or change their activity. One of the best studied oncogenes is “ras” which gets activated by a mutation.

Tumor suppressor genes code for proteins that regulate cell division. Tumor suppressors act like a brake pedal: if cells divide too quickly they halt the cell cycle. If tumor suppressor functions are lost, cells divide unchecked. Half of all human tumors contain mutations in a tumor suppressor gene called “p53”.

DNA repair genes code for proteins that normally repair mistakes that occur during DNA replication. Mutations in DNA repair genes allows mutations to accumulate. Cancers can occur when these mutations activate oncogenes or inactivate tumor suppressors.

Tutorial

How can we find out which genes are mutated in lung cancer? Use Entrez to search PubMed.

PubMed is a database, maintained by the National Library of Medicine, that provides access to over 12 million citations from MEDLINE and other databases of scientific literature. This tutorial shows:

• How to limit a search,
• How to use a wild-card operator (*)
• How combine queries so that are limits are applied to some terms but not others
• How to use History to keep track of search results
• The process used by Entrez to search PubMed

Programs and databases

• Netscape: Mac,   PC
• Internet Explorer: Mac, PC

Click on the green arrow to begin

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