What is the significance of a protein capsid in viruses?

The protein capsid plays a crucial role in the structure and function of viruses by protecting their genetic material. The capsid is a protein shell that encases the viral genome, which may consist of either DNA or RNA. This protection is vital for the integrity of the viral genetic information, especially since viruses are exposed to various environmental stressors, including enzymes that can degrade nucleic acids, as well as other immune responses from the host organism.

In addition to providing a protective barrier, the capsid is also important for the virus's ability to infect host cells. It facilitates attachment to host cell receptors, allowing the viral genome to be delivered into the host. This is essential for the virus's life cycle, as it needs to hijack the host's cellular machinery to replicate and produce new viral particles.

In contrast, the other options do not accurately reflect the role of the protein capsid. For instance, cellular respiration is a process specific to living cells and does not relate to the non-cellular nature of viruses. The capsid does not assist in replication of host DNA, as viruses replicate their own genetic material using the host's machinery, not by interacting directly with the host's DNA. Lastly, the function of converting amino acids into proteins relates to