According to the Baltimore model, viruses are classified based on which aspect of their life cycle?

• A. The shape and size of the viral capsid
• B. The host cell type they infect
• C. The type of nucleic acid and the method of mRNA synthesis
• D. The presence or absence of an envelope

Answer: (C)

Verified step by step guidance

1. Understand that the Baltimore classification system categorizes viruses based on their genetic material and how they produce messenger RNA (mRNA) during infection.
2. Recognize that the key factor in this classification is the type of nucleic acid the virus contains, which can be DNA or RNA, and whether it is single-stranded or double-stranded.
3. Identify the method by which the virus synthesizes mRNA, since this determines how the virus hijacks the host's cellular machinery to produce viral proteins.
4. Note that other characteristics such as the shape and size of the viral capsid, the host cell type, or the presence of an envelope are not the primary basis for Baltimore classification.
5. Conclude that the Baltimore model groups viruses into classes based on their nucleic acid type and the pathway they use to generate mRNA, which is essential for viral replication.