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All 7 Flashcards — Structure and diversity of viruses
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Question
Define a virus.
Answer
A **non-cellular infectious particle**: a **nucleic acid genome (DNA or RNA)** inside a **protein capsid**, sometimes with a lipid envelope. It replicates only inside a host cell.
Question
Why is a virus called non-cellular (acellular)?
Answer
It has **no cytoplasm, organelles, ribosomes or metabolism** — it is not built from cells.
Question
What two parts does every virus have?
Answer
A **genome** (DNA or RNA) and a **protein capsid** (built from capsomere sub-units).
Question
What is a capsid?
Answer
The **protein coat** surrounding a virus's genome, made of repeating sub-units called **capsomeres**; it protects the genome and helps attach to a host.
Question
What are the envelope and glycoprotein spikes for?
Answer
The **lipid envelope** (from the host membrane) surrounds the capsid; the **spikes** bind **specific host-cell receptors** so the virus can attach and enter.
Question
Name three ways viruses are diverse.
Answer
**Size**; **capsid shape** (helical / icosahedral / complex); and **genome type** (DNA vs RNA, single- vs double-stranded).
Question
What does 'obligate intracellular parasite' mean?
Answer
The virus **has no choice** but to be inside a **host cell** to replicate, using the host's **ribosomes and machinery**.
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Topic 1.5 hub
Viruses
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