property first discovered about viruses that distinguished them from other microorganisms?They were too large to pass through a 0.2-micron filterThey could reproduce only in brothThey made tobacco plants sickThey were small enough to pass through a 0.2-micron filterNone of the above3 All of us carry many different viruses throughout our daily lives. Why don’t they make us sick?
4 Why do we care that viruses comprise the most biodiversity on the planet?
5 The first viruses were discovered near the end of the 1800s. How was this done?By transmitting a disease to tobacco plants using a cell-free filtrate of diseased leavesPasteur showed that viruses could reproduce in a sterile mediumLeeuwenhoek saw viruses in his microscopeRobert Koch showed that viruses grown in broth could cause diseaseAll of the above
6 Why were the bacteriophage systems so useful for elucidating principles of viral reproduction? What important features of virus-host interactions were discovered from these studies?
7 How are viruses classified?
8 How does the discovery of new viruses today differ from 100 years ago?
9 Which host cell function is essential for the reproduction of all viruses?
10 What is the basis of the Baltimore classification system? How many genome types are sufficient to describe all viral families in this system?
2 The Infectious Cycle
The Infectious Cycle The Cell Entering Cells Viral RNA Synthesis Viral Protein Synthesis Viral Genome Replication Assembly of Progeny Virus Particles
Cultivation of Viruses Cell Culture Embryonated Eggs Laboratory Animals
Assay of Viruses Measurement of Infectious Units Efficiency of Plating Measurement of Virus Particles
Viral Reproduction: the Burst Concept
The One-Step Growth Cycle One-Step Growth Analysis: a Valuable Tool for Studying Animal Viruses
Global Analysis DNA Microarrays Mass Spectrometry Protein-Protein Interactions
LINKS FOR CHAPTER 2
Video: Interview with Dr. Thomas Hope http://bit.ly/Virology_Hope
Cloning HeLa cells with Philip I. Marcus http://bit.ly/Virology_Twiv197
Ode to a plaque http://bit.ly/Virology_Twiv68
Movie 2.1: Plaque formation by vesicular stomatitis virus http://bit.ly/Virology_VZVGFP
Think globally, act locally http://bit.ly/Virology_Twim90
You know my methods, Watson.
SIR ARTHUR CONAN DOYLE
Introduction
Viruses are unique: often made up of nothing more than a nucleic acid molecule wrapped in protein, they parasitize the cellular machinery to produce thousands of progeny. This simplicity is misleading: viruses can infect all known life forms, and they comprise a variety of structures and genomes. Despite such variety, viruses are amenable to study because all viral propagation can be described in the context of three fundamental properties, as noted in Chapter 1: viral genomes are packaged inside particles that mediate their transmission from cell to cell; the viral genome contains the information for initiating and completing an infectious cycle; viruses establish themselves in a host population to ensure virus survival.
How viruses enter individual cells, their genomes are replicated, and new infectious particles are assembled are some of the topics of research in virology. These studies are usually carried out with cell cultures because they are a much simpler and more homogeneous experimental system than animals. Cells can be infected in such a way as to ensure that a single reproduction cycle occurs synchronously in every infected cell, called one-step growth. A full understanding of viral infectious cycles also requires knowledge of cell biology. Consequently, to reproduce
