Question

Study the following statements (I - III) and select the correct option stating true (T) and false (F).

I. Proto oncogene is a normal cell growth regulator.
II. Oncogenic viruses transform cancerous cells to normal cells by binding with the host cell DNA.
III. Retrovirus incorporates genetic material from a host cell into its own genome upon infection, converting it into a viral oncogene.

Answer 1

Cancer is a dreadful disease in which some of the body cells grow uncontrollably and spread to other parts of the body.

Proto oncogene is a gene involved in normal cell growth. Mutations (changes) in a proto oncogene may cause it to become an oncogene, which can cause the growth of cancer cells.

The proto oncogene acts as a positive growth regulator by involve in promoting the differentiation and proliferation of normal cells. So that the normal cells attain a specific function and stop dividing. Hence statement I is true.

There are some viruses that can induce cancer and are known as oncogenic viruses. These viruses infect cells and cause transformation of the cells by converting it into tumors. Hence statement II is false.

When a retrovirus infects a cell it incorporates a part of the host cell genetic material (proto oncogene) into its own genome. This results in the conversion of proto oncogene to a viral oncogene. The single stranded RNA, carrying oncogene in virus is then converted into a double stranded DNA with the help of the enzyme reverse transcriptase during infection time. The newly formed viral oncogene carrying double stranded DNA infects another cell now. This new oncogene gets integrated into the cellular genome of the host. Upon expression of the viral oncogene in the host cell, the cells start dividing in an uncontrolled manner leading to neoplastic transformations (tumors) as shown in the image. Hence statement III is true.

Figure : Mechanism of action of viral oncogene