Question

Positive- and negative-strand RNA viruses require an ____-____________ _____ ___________, because the host cell does not have this type of enzyme?

Answer 1

RNA viruses require RNA-dependent RNA polymerase (RdRP) for replication, as this enzyme is not present in host cells. Positive-strand RNA can be directly used as mRNA, while negative-strand RNA must be converted by RdRP. Retroviruses like HIV use reverse transcriptase to transcribe RNA to DNA.

Step-by-step explanation:

Positive- and negative-strand RNA viruses require an RNA-dependent RNA polymerase (RdRP) for replication, because the host cell does not naturally have this type of enzyme. While positive-strand RNA viruses can use their RNA directly as mRNA for protein synthesis, negative-strand RNA viruses need the RdRP enzyme to convert their RNA into a complementary +ssRNA, which can then be used as mRNA by the host's ribosomes.

Retroviruses, such as HIV, utilize a different enzyme called reverse transcriptase to convert their RNA into DNA before integrating it into the host genome.

Answer 2

Positive- and negative-strand RNA viruses require an RNA-dependent RNA polymerase (RdRP) for their replication process, because host cells lack this enzyme. The RdRP synthesizes positive RNA from the negative-strand RNA template, enabling the production of viral proteins and further replication.

Step-by-step explanation:

Positive- and negative-strand RNA viruses require an RNA-dependent RNA polymerase (RdRP) for replication, because the host cell does not have this type of enzyme. This enzyme is critical for the replication process of RNA viruses.

When a virus with a negative single-strand RNA (-ssRNA) genome infects a host cell, the host's ribosomes cannot directly translate this strand into proteins. This is because the -ssRNA is complementary to the host's mRNA. Therefore, the virus must bring in its own RdRP to replicate the -ssRNA into positive single-strand RNA (+ssRNA), which can then be translated by the host's ribosomes. RdRP also plays a crucial role in the replication of double-stranded RNA (dsRNA) viruses by using the negative strand of the dsRNA as a template to create +ssRNA.

In contrast, positive-strand RNA (+ssRNA) viruses can have their genome directly act like mRNA and be translated by the host cell ribosomes to produce viral proteins. However, for the synthesis of new viral RNA strands, RdRP is also utilized to create the complementary negative-strand RNA, serving as a template for further production of +ssRNA.