Download Retro = backward

Intro to Viruses
Learning Objectives - Viruses
• Be able to
– Describe the basic structure of a virus
– Explain why viruses are classified as non-living
What are Viruses?
• Particles of nucleic acid, protein and in some
cases, lipids
• Reproduce by infecting living cells
• Differ widely in terms of size and structure
• Enter cells and use the machinery of the
infected cell to produce more viruses
Are Viruses Living?
• According to the online Merriam-Webster Dictionary
life is
– “an organismic state characterized by capacity for metabolism,
growth, reaction to stimuli, and reproduction.”
• Viruses are NOT living things
• Complicated assemblies of molecules (including proteins,
nucleic acids)
• Cannot do anything on their own – they MUST enter a living
cell
• Without cells, viruses would not be able to multiply
Virus Structure
• Typical virus is made of
– Core DNA or RNA
– Surrounded by protein coat
– (sometimes) contain layer of fat
• Simplest viruses contain a few
genes
– Most complex can have > 100
genes
• Protein coat of a virus is called it’s capsid
• Includes proteins that enable a virus to enter
host cell
• Capsid proteins of viruses bind to receptors on
cell’s surface
– They “trick” the cell into allowing it inside
• Once inside, the viral genes are expressed
– Cell transcribes and translates the viral genetic
information into viral capsid proteins
Retrovirus
What is it?
• Contain RNA as their
genetic material
• Genetic information is
copied backwards
– From RNA to DNA (instead of
DNA to RNA)
• Retro = backward
• Responsible for some types
of cancers in animals,
humans
• Causes AIDS
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Infect cells
Produce a DNA copy of their RNA
Insert this DNA into host cell
Dormant before active
Production of new virus results in death of
host cell