Viruses

1. Viruses Ooo la la

2. Viral Infection Once inside the cell, 2 different processes can occur – lytic or lysogenic.

3. Lytic Infection A virus enters the cell, makes copies of itself and causes the cell to burst.

4. For example: • Bacteriophage T4 injects its own DNA directly into the cell.

5. 2) The cell begins to make mRNA from the genes of the virus. 3) The viral mRNA is translated into viral proteins that begin to chop up the cell DNA, which shuts down the infected cell.

6. 4) The virus then uses these materials to make thousands of copies of its own DNA molecules. The viral DNA gets assembled into new virus particles. 5) Before long, the host cell lyses, or bursts, and releases hundred of viruses that may go on to infect other cells.

7. Lysogenic Infection A virus integrates its DNA into the DNA of the host cell, and the viral genetic information replicates along with the host cell’s DNA.

8. Lysogenic Infection • Lysogenic viruses can remain inactive for a period of time, unlike the lytic infection when the host cell bursts right away.

9. Lysogenic Infection • The viral DNA becomes embedded in the host’s DNA and is called a prophage. This prophage may remain part of the DNA in the host cell for many generations before becoming active. • Eventually, one of a number of factors, may activate the DNA of a prophage, which will then remove itself from the host cell DNA and begin to make new viruses.

11. RetrovirusesRNADNA • Some viruses contain RNA, instead of DNA. • When retroviruses infect a host cell, they produce a DNA copy of their RNA. This is backwards as mRNA is usually formed from DNA – hence the name “retro.” • Retroviruses can remain dormant before becoming active and causing the host cell to die.

12. Retroviruses Some cancers are caused by retroviruses (oncogenic = cancer-causing) and HIV, which causes Acquired Immune Deficience Syndrome (AIDS) is caused by a retrovirus.