Microbiology Practice Exam

The outer protein coat of a simple virus particle is known as the capsid. The capsid serves crucial functions in the life cycle of a virus. It protects the viral genetic material from degradation by enzymes and helps the virus attach to and penetrate host cells. The capsid is typically composed of protein subunits called capsomers, which assemble to form a protective shell around the viral genome.

In contrast, the envelope refers to a lipid bilayer that some viruses possess, which is derived from the host cell membrane but is not part of the basic structure of all viruses. It provides an additional layer of protection and can play a role in the process of viral entry into host cells. The matrix is more associated with the region between the capsid and the envelope in enveloped viruses, helping to stabilize the structure. The term pellicle generally refers to a thin film or coating and is not commonly used in virology to describe the outer structure of viruses.

Thus, within the context of a simple virus particle, the term capsid accurately describes the outer protein coat.