Molecular Basis of Cancer
Development of cancer results from the genetic change in a single cell that further
leads to the uncontrolled multiplication of the cells. Therefore, the multiplication in
case of cancer is monoclonal.
There are two types of regulatory genes present in the cells- oncogenes and
antioncogenes. There is a third category of genes that are responsible for apoptosis
and they are also involved in cancer.
Oncogenes: the genes that are capable of causing cancer are known as oncogenes.
The viral oncogenes are almost similar to some of the genes that are present inside
the normal cells of the host and these are known as protooncogenes. These
protooncogenes encode for the growth regulating proteins.
In order to cause cancer, these protooncogenes need to be activated. There are
different factors that can activate the protooncogenes to oncogenes and that leads
to cancer.
• Viral insertion into chromosome
Protooncogenes can be activated when the viral genome is inserted into the
host chromosome. Some RNA viruses infect the host cells and then make a
complementary DNA by the help of the enzyme reverse transcriptase. This
complementary DNA gets inserted inside the host cell DNA or genome. The
integrated cDNA into the host genome is known as provirus.
The provirus takes the control over the host cell machinery and the processes
like replication and transcription of host DNA and starts transforming the
normal cells into viral particles.
This can be seen in the case of Avian leukemia where viral infection causes the
activation of protooncogene myc to oncogene.
• Chromosomal translocation
The process of translocation involves the rearrangement of genes in the
chromosomes. In this phenomenon, a small fragment of chromosome is split
off and it joins to another chromosome. This leads to the over-expression of
Development of cancer results from the genetic change in a single cell that further
leads to the uncontrolled multiplication of the cells. Therefore, the multiplication in
case of cancer is monoclonal.
There are two types of regulatory genes present in the cells- oncogenes and
antioncogenes. There is a third category of genes that are responsible for apoptosis
and they are also involved in cancer.
Oncogenes: the genes that are capable of causing cancer are known as oncogenes.
The viral oncogenes are almost similar to some of the genes that are present inside
the normal cells of the host and these are known as protooncogenes. These
protooncogenes encode for the growth regulating proteins.
In order to cause cancer, these protooncogenes need to be activated. There are
different factors that can activate the protooncogenes to oncogenes and that leads
to cancer.
• Viral insertion into chromosome
Protooncogenes can be activated when the viral genome is inserted into the
host chromosome. Some RNA viruses infect the host cells and then make a
complementary DNA by the help of the enzyme reverse transcriptase. This
complementary DNA gets inserted inside the host cell DNA or genome. The
integrated cDNA into the host genome is known as provirus.
The provirus takes the control over the host cell machinery and the processes
like replication and transcription of host DNA and starts transforming the
normal cells into viral particles.
This can be seen in the case of Avian leukemia where viral infection causes the
activation of protooncogene myc to oncogene.
• Chromosomal translocation
The process of translocation involves the rearrangement of genes in the
chromosomes. In this phenomenon, a small fragment of chromosome is split
off and it joins to another chromosome. This leads to the over-expression of
