<p> Life Cycles of a Virus </p><p>Virus Specificity:</p><p>- Plant viruses can only infect plants</p><p>- Bacteriophages can only infect bacteria</p><p>- Most viruses only infect one host (Ex – Measles only infect humans)</p><p>- Some viruses can infect more than 1 host (Ex – Rabies can infect mammals and birds </p><p>Life Cycles of a Virus :</p><p>- In order for a virus to reproduce it must invade, or infect a living host cell.</p><p>- There are two ways in which a virus can infect a cell: 1. Lytic Infection: The process by which a host cell is invaded, lysed and destroyed by a virus</p><p>Lytic Life Cycle (Ex- Bacteriophage)</p><p>1. Adsorption Virus comes in contact with host cell by chance. Macromolecules on tail fibers of T4 phage attach to receptors on cell wall of the bacterium.</p><p>2. Penetration  A phage injects its DNA into the host’s cytoplasm </p><p>3. Replication The virus takes over and uses material of the host cell to make copies of its own protein coat and DNA 4. Assembly  Assembly of phage parts around the new copies of DNA. </p><p>5. Lysis  The infected cell lyses (bursts) and releases hundreds of virus particles which may now go and infect other cell</p><p>2. Lysogenic Infection Process in which viral DNA is inserted into the DNA of a host cell by where it can remain for many generations before becoming active</p><p>Lysogenic Life Cycle (Ex –lambda, which infects E.coli)</p><p>1. Adsorption – By chance virus come in contact with host. Lysogenic phage uses molecules on tail fibers attach to receptors located on cell wall of bacterium </p><p>2. Penetration  Bacteriophage injects viral DNA into the cytoplasm of the host cell.</p><p>3. Integration  Bacteriophage’s genetic material is incorporated into bacterium’s DNA </p><p>**bacteriophage DNA may replicate within bacterium for several generations -Once viral DNA has been inserted into host cell’s DNA the viral DNA is referred to as a Prophage.</p><p>4. Removal Conditions change (sudden change in temp and availability of nutrients cause the DNA of prophage to become active. DNA removes itself from DNA of host cell. </p><p>5. Synthesis  Viral DNA directs the synthesis of new viral particles (DNA and protein parts)</p><p>6. Assembly  Assembly of phage parts around the new copies of DNA. </p><p>7. Lyses  Bacteriophage enzyme lyses the bacterium’s cell wall and the new viruses are released. </p>