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I. Introduction
II. Viruses
A. Definition
1. Obligate Intracellular Parasites
a. Infect all kingdoms
B. Size
1. 20 nm (some parvoviruses)
2. 250 nm (some poxviruses)
3. >400 nm (mimiviruses)
C. Structure
1. Core Viral Genome
a. DNA or RNA
2. Capsid
a. Protective protein covering
b. Capsomeres
c. Shape
3. Nucleocapsid
a. Genome + Capsid
4. Envelope (some)
a. Membrane-like
i. proteins, lipids, viral components
b. Spikes
i. Recognize host cell receptors
5. Virion
a. Complete, assembled virus outside host
III. Classification
A. General Comments
1. No agreed upon classification system
2. Can be based on type, size, structure,
organism infected, disease produced, etc.
B. Names
1. No agreed upon naming system
2. Can be based on tissue infected, geography,
discoverers, etc.
C. Suggested Classification Scheme
1. Families (73)
a. Name ends in -viridae
i. Example: Herpesviridae
2. Genera
a. Name ends in -virus
i. Example: Herpesvirus
3. Species
a. No agreed upon naming convention
b. Generally a common name based on
disease (hepatitis virus, smallpox virus)
or some other characteristic
4. Strains
a. Based on variations of chemical
structure and infectivity
IV. Infection
A. General Comments
1. Varies based on type of virus and host
B. Basic Steps
1. Attachment
a. Virus attaches to host cell membrane
using cell membrane receptors
2. Penetration (Types)
a. Whole virus enters cell
b. Viral envelope merges with host cell and
nucleopcapsid enters cell
c. Only viral genome enters cell
3. Biosynthesis and Maturation
a. Biosynthetic mechanisms of host cell
“taken over” to make virus particles
b. Viral DNA or RNA replicated
i. DNA Virus:
DNA --> DNA;
DNA --> RNA --> Protein
ii. RNA Virus:
RNA --> RNA;
RNA --> Protein
iii. Retrovirus:
RNA --> DNA;
DNA --> RNA --> Protein
c. Viral components synthesized;
new viruses formed
4. Release
a. New virus released through budding
or lysis
V. Summary
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