State the features of viruses, limited to a protein coat and genetic material.

1.3 Features of Organisms – Viruses

What is a Virus?

A virus is a microscopic parasite that can only reproduce inside a living cell. Think of it as a tiny delivery truck that carries a message (its genetic material) into a cell and hijacks the cell’s machinery to make more trucks. 🚚

Key Features of Viruses

• Very small – usually 10–300 nm in diameter.
• Only contain a protein coat (capsid) and genetic material ($DNA$ or $RNA$).
• No cell membrane – they lack the complex structures of living cells.
• Cannot carry out metabolic processes on their own.
• Must infect a host cell to replicate.

Structure of a Virus

1. Capsid – a protein shell that protects the genetic material. Imagine a sturdy cardboard box that keeps the contents safe.
2. Genetic material – either single‑stranded or double‑stranded $DNA$ or $RNA$. This is the “instruction manual” the virus uses to hijack the host cell.
3. Optional envelope – some viruses have a lipid membrane derived from the host cell, like a borrowed coat that helps them sneak in.

Analogy: Virus as a “Trojan Horse”

Just as the ancient Greeks used a wooden horse to sneak soldiers into Troy, a virus uses its capsid to sneak its genetic material into a host cell. Once inside, the cell’s machinery is tricked into building more viruses, just like the hidden soldiers would start building more horses inside the city. 🐴

Comparison Table: Viruses vs. Cells

Exam Tip Box