Correct option is D
Correct Answer: (d)
Explanation: Retroviruses do not cause cancer solely by directly mutating host DNA. Their oncogenic potential mainly arises through integration into the host genome, leading to insertional mutagenesis or activation of host proto-oncogenes, or by carrying viral oncogenes derived from host genes. Therefore, the statement suggesting cancer induction without integration or proto-oncogene activation is false.
Information Booster
· Retroviral integration into the host genome is a key step in oncogenesis.
· Some retroviruses carry viral oncogenes that drive rapid tumor formation.
· Slow-transforming retroviruses act by activating nearby host proto-oncogenes.
· DNA tumor viruses encode proteins that interfere with cell cycle control.
· Viral oncogenesis provides important insights into cancer biology.
Additional Knowledge
Rous sarcoma virus is a classic example of a fast-acting retrovirus that carries the v-src oncogene, originally derived from the host c-src proto-oncogene. Slow-acting retroviruses lack oncogenes but induce cancer through insertional activation of host growth-promoting genes. DNA viruses such as papillomaviruses and adenoviruses contribute to cancer by expressing viral proteins that deregulate cell cycle checkpoints. These mechanisms clearly show that retrovirus-induced cancer requires integration-dependent processes rather than simple direct mutation of host DNA.
