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Viral Structure

A Brief Look at the Structure of Viruses Mr. Chapman Biology 20. Viral Structure. Viruses are Very Small. Viruses are much smaller than plant and animal cells, and also much smaller than bacterial. Viruses range in size from 18 – 300 nm. Note that 1 nanometre = 1 x 10 -9 m.

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Viral Structure

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  1. A Brief Look at the Structure of Viruses Mr. Chapman Biology 20 Viral Structure

  2. Viruses are Very Small • Viruses are much smaller than plant and animal cells, and also much smaller than bacterial. • Viruses range in size from 18 – 300 nm. Note that 1 nanometre = 1 x 10-9 m.

  3. Viruses Have a Very Simple Structure • A virus is simply made of genetic material (either RNA or DNA) surrounded by a protein shell called a capsid.

  4. Properties and Structure • A single viral particle is called a virion. • Capsids (the protein structure on the outside of the virus) are different shapes for different viruses, and some are covered by a lipid (a.k.a. Fat) envelope. • The lipid envelope is the protective outer coat of a virus, from which spiky structures from proteins or sugars sometimes stick out.

  5. Structure Continued... • A virus is called a naked virus when it consists of only the genetic material surrounded by a capsid(no lipid envelope).

  6. Viral Structure • In some viruses, capsids form a 20-sided polyhedron. • Other viruses are rod-like, and some strand-like viruses are shaped in coils, like a spring or a helix. • Unlike prokaryotes and eukaryotes, viruses have DNA or RNA, but never both.

  7. Importance of Structure / Shape • The structure and shape of particular viruses are very important. • A virus can only infect certain hosts, and it identifies its hosts by fitting its surface proteins to receptor molecules on the surface of the host cell. • The system is like a lock and key, and viruses need the correct key to infect a particular cell.

  8. Is a Virus Alive? Believe it or not, the answer is not clear.

  9. Viral Structure – Not Much Structure at All • Unlike other types of cells, a virus really has no structure to maintain at all. • Viruses don’t eat, excrete, use energy, or require oxygen at all. They don’t have organelles, either In fact, they do almostnothingthat living organisms do – except reproduce. • Even so, a virus can only reproduce after it has infected a host cell.

  10. Comprehension Questions • What are the three main components of a typical virus? Which one of these components is a naked virus missing? • How does the size of a virus compare to that of a plant or animal cell? • Why are the structures protruding from the lipid envelope important for bonding to host cells? • Why is it unclear as to whether or not a virus is alive?

  11. Conclusion... For Now! Complete the rest of the class by reading section 18.2 of the Biology textbook, and complete questions 1 – 4 on page 551.

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