Question

Why are nucleoside analogs active only against replicating viruses?

1) These drugs can only be taken up by cells that are infected by viruses. They are shut out from non-infected cells. This makes them effective only against cells where viruses are replicating.
2) Each of these drugs is specifically activated by enzymes produced by the viruses. The viruses will only produce these enzymes when they are replicating, so the drugs can only become activated when these processes are occurring.
3) Nucleoside analogs work by directly inhibiting the activity of nucleic acid polymerases. If the virus isn't actively replicating, there's no DNA/RNA polymerase active for the drug to inhibit, so the drug cannot work.
4) Nucleoside analogs work by being incorporated into growing strands of DNA/RNA. This indirectly shuts down further extension of these chains. However, new strands of viral DNA/RNA are only being created when the virus is replicating. Thus, these drugs can only work when the virus is actively replicating as well.
5) Nucleoside analogs work by being incorporated into growing strands of amino acids during enzyme synthesis. This indirectly shuts down further extension of these chains. However, new viral proteins are only being created when the virus is replicating, so these medications only work if that is the case.

Answer 1

Nucleoside analogs are active only against replicating viruses because they can only enter infected cells, are specifically activated by viral enzymes, inhibit nucleic acid polymerases, and interfere with DNA/RNA synthesis and protein synthesis.

Step-by-step explanation:

Nucleoside analogs are active only against replicating viruses for several reasons:

1. These drugs can only be taken up by cells that are infected by viruses.
2. Each of these drugs is specifically activated by enzymes produced by the viruses.
3. Nucleoside analogs work by directly inhibiting the activity of nucleic acid polymerases.
4. Nucleoside analogs work by being incorporated into growing strands of DNA/RNA.
5. Nucleoside analogs work by being incorporated into growing strands of amino acids during enzyme synthesis.

These drugs are not effective against non-replicating viruses or healthy cells because they cannot enter non-infected cells, the enzymes needed to activate them are only produced during viral replication, there are no active nucleic acid polymerases to inhibit in non-replicating viruses, and there are no growing strands of DNA/RNA or amino acids during enzyme synthesis in non-replicating viruses.