VirusVirus-particles of -particles of nucleic acid, nucleic acid, proteins and in proteins and in some cases, lipids.some cases, lipids.

A typical virus is A typical virus is composed of a core composed of a core of DNA or RNA of DNA or RNA surrounded by a surrounded by a protein coat.protein coat.

CapsidCapsid-virus’ -virus’ protein coat.protein coat.

Virus Structure

General InformationGeneral Information Have one thing in common:They enter Have one thing in common:They enter

living cells and once inside use the living cells and once inside use the machinery of the infected cell to produce machinery of the infected cell to produce more virusesmore viruses

Viruses can only reproduce by infecting Viruses can only reproduce by infecting living cells.living cells.

Viruses have to bind precisely to proteins Viruses have to bind precisely to proteins on the cell surface and then use a host’s on the cell surface and then use a host’s genetic system, so most viruses are highly genetic system, so most viruses are highly specific to the cells they infect. specific to the cells they infect.

Lytic InfectionLytic Infection

In a lytic infection, a virus enters a cell, In a lytic infection, a virus enters a cell, makes copies of itself, and causes the cell makes copies of itself, and causes the cell to burst.to burst.– Example:BacteriophageT4.Example:BacteriophageT4.

DNA core is activated by contact with the host cell.DNA core is activated by contact with the host cell. Injects DNA directly into host cell.Injects DNA directly into host cell. Host cell can’t tell the difference so, the host cell Host cell can’t tell the difference so, the host cell

begins to make messenger RNA from genes of the begins to make messenger RNA from genes of the virus.virus.

The viral mRNA is translated into viral The viral mRNA is translated into viral proteins that chop up the host cell’s DNA proteins that chop up the host cell’s DNA which shuts down the cellwhich shuts down the cell

The virus uses the material of the host cell The virus uses the material of the host cell to make thousands of copies of its own DNAto make thousands of copies of its own DNA

The viral DNA assembles into new virusesThe viral DNA assembles into new virusesThe host cell lyses, or bursts, releasing The host cell lyses, or bursts, releasing

hundreds of virus particles hundreds of virus particles

Lysogenic InfectionLysogenic Infection In a lysogenic infection a virus integrates In a lysogenic infection a virus integrates

its DNA onto the DNA of the host cell, and its DNA onto the DNA of the host cell, and the viral genetic information replicates the viral genetic information replicates along with the host cell’s DNAalong with the host cell’s DNA

ProphageProphage-the viral DNA that is embedded -the viral DNA that is embedded in the host’s DNAin the host’s DNA

Prophage may remain part of the DNA for Prophage may remain part of the DNA for generations before becoming activegenerations before becoming active

Once active it acts the same as a lytic Once active it acts the same as a lytic infectioninfection

Bacteriophages-Bacteriophages-viruses that infect bacteriaviruses that infect bacteria RetrovirusesRetroviruses-viruses that contain RNA as -viruses that contain RNA as

their genetic informationtheir genetic information When a retrovirus infects a cell, they insert a DNA When a retrovirus infects a cell, they insert a DNA

copy of their RNA into the DNA of the host cell, where copy of their RNA into the DNA of the host cell, where it may remain dormant for a length of timeit may remain dormant for a length of time

Retroviruses get their name because they copy Retroviruses get their name because they copy backwards: RNA-DNAbackwards: RNA-DNA

Responsible for some types of cancer and AIDSResponsible for some types of cancer and AIDS

Are Viruses Alive?Are Viruses Alive? YESYES

– Can reproduceCan reproduce– Regulate gene Regulate gene

expressionexpression– Can evolveCan evolve– Parasites Parasites

NONO– Not made up of Not made up of

cellscells– Can’t live Can’t live

independentlyindependently

Life SciencesLife Sciences Used in the study of molecular and cellular Used in the study of molecular and cellular

biology, as they provide simple systems that can biology, as they provide simple systems that can be used to manipulate and investigate the be used to manipulate and investigate the function of cells.function of cells.

Used in the study of genetics, helped with Used in the study of genetics, helped with understanding the basic mechanisms of understanding the basic mechanisms of molecular genetics, such as DNA replication, molecular genetics, such as DNA replication, transcription, RNA processing, translation, protein transcription, RNA processing, translation, protein transport and immunology.transport and immunology.

Materials-Science Materials-Science and Nanotechnologyand Nanotechnology

April 2006April 2006– Scientists at the Massachusetts Institute of Scientists at the Massachusetts Institute of

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

WeaponsWeapons There is a fear that viruses may be There is a fear that viruses may be

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

                          

Last Known CaseLast Known Case 1978 1978

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

Aftermath of 1978 Aftermath of 1978 CaseCase As a result of the 1978 case, all stocks As a result of the 1978 case, all stocks

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

Recent ScaresRecent Scares March 2003March 2003

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

QuizQuiz What are the two types of viral What are the two types of viral

infections? infections? What is a retrovirus?What is a retrovirus? What is a bacteriophage?What is a bacteriophage? What is a practical use of a virus?What is a practical use of a virus? Why are viruses very specific to the Why are viruses very specific to the

cells they infect?cells they infect?