Introduction: the structural basis of virus function.

Viruses may be regarded as dynamic nucleoprotein assemblies capable of assisted multiplication within cells, and of propagation between cells and organisms. Infectious virus particles (virions) assembled in a host cell are dynamic, generally metastable particles: They are robust enough to protect the viral genome outside the cell, but are also poised to undergo structural changes and execute mechanochemical actions required for infection of other cells. This chapter provides an introduction to the structural and physical biology of viruses by including: (i) an elementary overview on virions and the structural basis of virus function; (ii) a concise summary on basic techniques used in structural or physical virology; (iii) brief structure-based general descriptions of the different stages in the virus cycle, especially those in which virions and/or their components are involved. These contents may facilitate a better understanding of the specialized subjects treated in the rest of the book. This chapter is also intended as a "road map" to help interconnect and integrate in a single picture the different topics described in depth in the 21 monographic chapters in this book.