 Virus-particles of nucleic acid, proteins and in some cases, lipids.  A typical virus is composed of a core of DNA or RNA surrounded by a protein coat.  Capsid-virus’ protein coat. Virus Structure

General Information  Have one thing in common:They enter living cells and once inside use the machinery of the infected cell to produce more viruses  Viruses can only reproduce by infecting living cells.  Viruses have to bind precisely to proteins on the cell surface and then use a host’s genetic system, so most viruses are highly specific to the cells they infect.

Lytic Infection  In a lytic infection, a virus enters a cell, makes copies of itself, and causes the cell to burst. –Example:BacteriophageT4.  DNA core is activated by contact with the host cell.  Injects DNA directly into host cell.  Host cell can’t tell the difference so, the host cell begins to make messenger RNA from genes of the virus.

 The viral mRNA is translated into viral proteins that chop up the host cell’s DNA which shuts down the cell  The virus uses the material of the host cell to make thousands of copies of its own DNA  The viral DNA assembles into new viruses  The host cell lyses, or bursts, releasing hundreds of virus particles

Lysogenic Infection  In a lysogenic infection a virus integrates its DNA onto the DNA of the host cell, and the viral genetic information replicates along with the host cell’s DNA  Prophage-the viral DNA that is embedded in the host’s DNA  Prophage may remain part of the DNA for generations before becoming active  Once active it acts the same as a lytic infection

 Bacteriophages-viruses that infect bacteria  Retroviruses-viruses that contain RNA as their genetic information  When a retrovirus infects a cell, they insert a DNA copy of their RNA into the DNA of the host cell, where it may remain dormant for a length of time  Retroviruses get their name because they copy backwards: RNA-DNA  Responsible for some types of cancer and AIDS

Are Viruses Alive?  YES –Can reproduce –Regulate gene expression –Can evolve –Parasites  NO –Not made up of cells –Can’t live independently

Life Sciences  Used in the study of molecular and cellular biology, as they provide simple systems that can be used to manipulate and investigate the function of cells.  Used in the study of genetics, helped with understanding the basic mechanisms of molecular genetics, such as DNA replication, transcription, RNA processing, translation, protein transport and immunology.

Materials-Science and Nanotechnology  April 2006 –Scientists at the Massachusetts Institute of Technology created nanoscale metallic wire using a genetically-modified virus. The MIT team was also able to create a battery with an energy density three times more than current materials; this technology can be used in liquid crystals, solar cells, fuel cells, and other electronics in the future.

Weapons  There is a fear that viruses may be used as biological weapons.One of the main viral candidates is small pox because it is completely eradicated in nature and an epidemic would be devastating due to low immunity and high mortality rates.

Last Known Case  1978 –Virus escaped from a containment research laboratory in Birmingham, England. Janet Parker contracted the disease and died, and Professor Henry Bedson, who was responsible for the unit, killed himself from guilt.

Aftermath of 1978 Case  As a result of the 1978 case, all stocks were ordered to be destroyed except for a stock in Atlanta, GA for the Center for Disease Control and in the Russian Vector State Research Center of Virology and Bacteriology in Siberia. These stocks were ordered to be destroyed in 1993, 1994, 1995, and 1996, but are still in existence because a number of scientists wish to keep them for scientific purposes.

Recent Scares  March 2003 –Small pox scabs were found in an envelope in a book on Civil War Medicine in Santa Fe, New Mexico. This raised the fear that small pox DNA could be extracted from these and other scabs and used as a biological weapon.

Quiz  What are the two types of viral infections?  What is a retrovirus?  What is a bacteriophage?  What is a practical use of a virus?  Why are viruses very specific to the cells they infect?