Viral Structure Essentials

Steps:

• Recall that viruses are acellular and consist of genetic material enclosed in a protein shell.
• Identify the universal component: all viruses have a capsid protecting their nucleic acid.
• Evaluate each option against known viral diversity, including DNA/RNA types and enveloped/non-enveloped forms.
• Confirm the option that applies to every virus without exception.

Why A is correct:

• By definition, a capsid is the protein coat that all viruses use to encase and protect their genetic material (DNA or RNA).

Why the others are wrong:

• B: Some viruses have DNA genomes, not RNA (e.g., adenoviruses).
• C: Only enveloped viruses have a phospholipid outer layer; non-enveloped ones lack it (e.g., poliovirus).
• D: Viruses do not contain ribosomes of any size; they rely on host cell machinery for protein synthesis.

Final answer: A