1. Genetics of Viruses

2. What Are Viruses?
Viruses are tiny ( nm) particles composed of a nucleic acid core (either DNA or RNA) surrounded by a protein coat (capsid) and sometimes a membrane envelope (derived from its host cell)
Viruses are incapable of reproduction independent of host cells whose cellular machinery is taken over by the virus and used as a factory for producing new viruses

3. Viral Structure Viruses are made of a maximum of three basic parts:
Genetic material:
DNA viruses - Single or double stranded DNA
RNA viruses - Single or double stranded RNA
Capsid - A protein coat made up of one or a few capsomere proteins
Envelope - Not all viruses have an envelope which is derived from the host cell’s membrane
The envelope may contain proteins which assist in attachment and entry into new host cells

4. Phage Reproduction: The Lytic Cycle
Destruction of the bacteria’s DNA
Infection
Replication of the viral genome
Production of viral parts
Packaging
Lysis

5. Phage Reproduction: The Lysogenic Cycle
Circularization of phage DNA
Infection
Many generations of bacteria
Temperate phage
Exit of phage
Integration of phage DNA into the bacterial genome
On to the lytic cycle

6. Are Viruses Alive?
Viruses require cells to reproduce and do not have cells of their own, thus they do not fit the Cell Theory which states that being made out of cells is a characteristic of living things
Are viruses “missing links” between living and non-living things?
No, viruses require cells to reproduce, so cells had to come first then viruses thus viruses cannot serve as a “missing link” between living and non-living things