Question

What are the two reasons as to why DNA from non-tumor virus induced cannot transform normal cells?

Answer 1

Non-tumor viruses cannot transform normal cells due to limited replication machinery and dysregulation of checkpoint functions.

Step-by-step explanation:

The two reasons why DNA from non-tumor virus induced cannot transform normal cells are:

1. Limited Replication Machinery: Non-tumor viruses usually have a small genome that does not encode all the necessary enzymes and factors required for viral DNA replication. Therefore, they rely on the host cell's replication machinery to replicate their DNA. However, host cells only produce these factors during the S phase, and non-tumor viruses cannot induce the production of these factors at other times. This limitation prevents the viral DNA from replicating and transforming normal cells.
2. Dysregulation of Checkpoint Functions: Non-tumor viruses, like SV40, produce proteins that interfere with the normal checkpoint functions of the host cell. For example, SV40's large T antigen binds to p53, a protein involved in checkpoint functions, and disrupts its normal activity. As a result, the host cell loses control over cell division and can divide uncontrollably, leading to the formation of cancerous tumors.