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Viruses
2002
General structure
 Capsid: protein coat around the virus
 Nucleic acid: either RNA or DNA
 Tail fibers: attach to host at receptor site; lock and key fit with host cells/tissues
 Viral envelope: membrane derived from host cells with both host and viral
membrane proteins
General information
 They are the smallest and simplest pathogens
 Have no cellular structures
 Carry out no life functions by themselves
 Are obligate intracellular parasites (need a host for reproduction)
Types of reproduction
 A. Virulent viruses use the lytic cycle to reproduce
1. attachment
2. entry
3. replication
4. assembly
5. release
 B. temperate viruses use the lysogenic cycle
1. Attachment
2. Entry
3. Provirus formation
4. Activation
5. Replication
6. Assembly
7. Release
 C. Retroviruses: RNA viruses which form proviruses
1. Viral RNA enters the cell and is transcribed into DNA using reverse
transcriptase
2. Provirus formation; viral DNA is replicated with the host DNA
3. Viral proteins are made as the cell makes host proteins
4. Assembly and exocytosis covered in the host cell membrane
5. Cell never enters the lytic cycle but will make viruses for its entire life
span
Prions
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Prions are infectious proteins
Normal proteins are misfolded into prions
Prions can catalyze the refolding of the normal protein into the mutant form
Cause diseases like scrapie, BSE, CJD, kuru, etc