What is the first step of a virus's life cycle when infecting an animal cell?

• A. Assembly of new virions
• B. Uncoating of the viral genome
• C. Replication of viral nucleic acid
• D. Attachment to the host cell

Answer: (D)

Verified step by step guidance

1. Understand that the virus life cycle begins with the virus interacting with the host cell. The very first step is the virus recognizing and binding to specific receptors on the surface of the animal cell. This process is called attachment or adsorption.
2. Attachment is crucial because it determines the host range and specificity of the virus. Without attachment, the virus cannot enter the cell or initiate infection.
3. After attachment, the virus proceeds to penetrate the host cell, followed by uncoating, replication, assembly, and release. But these steps come after the initial attachment.
4. Therefore, when identifying the first step in the viral life cycle, focus on the interaction between viral surface proteins and host cell receptors, which is the attachment phase.
5. In summary, the first step is 'Attachment to the host cell,' which sets the stage for all subsequent steps in the viral infection process.