1. VIRUSES

2. Viruses Are Not Cells!
There are several structural and functional differences between cells and viruses
The structural differences include:
No nucleus
No cell membrane
No organelles
The functional differences include:
Do not grow
Do not respire
Do not develop
Do not reproduce

3. Viral Structure Viruses are made up of 2 parts:
Capsid—a protein coat which enables the virus to bind to a cell
Nucleic acid—either DNA or RNA
Some viruses have an additional protective coating called an envelope

4. Replication vs. Reproduction
Viruses do not reproduce
Viruses replicate
Reproduction requires cell division and replication does not
A virus requires a host for it to replicate
A host is a living cell that provides all the materials a virus needs to replicate

5. Classification of Viruses
Shape: allows viruses to attach to only a few kinds of cells; like two pieces of a jigsaw puzzle
Filovirus—has no distinct shape
Ebola- Zaire Ebola Virus, has the highest case-fatality rate, up to 90%. Massive blood loss leads to death.
Polyhedral virus—multifaceted geometric shape
Herpesvirus- Cold sores, shingles, virus lays dormant along nerve fibers

6. Binal virus—has a polyhedral capsid and a helical tail
Bacteriophage T4- virus which infects E.Coli. for molecular biology research
Helical virus—tightly coiled DNA or RNA inside a long, narrow capsid
Tobacco Mosaic Virus-infect members of nine plant families, 125 individual species

7. Classification of Viruses (cont.)
Host:
Plant virus
Animal virus
Bacterial virus—these are also called bacteriophages

8. Lytic Cycle Bacteriophage Bacterial chromosome DNA or RNA Entry
Bacterial host cell
Attachment
Lysis and
Release
Replication
Assembly

9. Lysogenic Cycle Prophage Entry: Lysis & Release: Assembly:
Not pictured
Prophage
Replication:

10. 1. RNA & reverse transcriptase enter the host cell
Retrovirus
Contains an RNA core that is replicated by 1st transcribing its RNA into DNA
Ex: HIV—the virus that infects white blood cells and causes AIDS
1. RNA & reverse transcriptase enter the host cell
2. Enzymes copy the viral RNA into DNA
4.Viral DNA produces new viruses
3. Viral DNA attaches to cell DNA

11. Nonviral Particles Viroid: Prion: No capsid Contains RNA
Cause plant diseases
Prion:
Protein molecule with no RNA or DNA
Cause animal diseases (i.e. mad cow disease)