Viruses The “tiny” guys.

Wendell Stanley First isolated virus in 1933, the purified extract crystallized. First isolated virus in 1933, the purified extract crystallized. Worked with the Tobacco Mosaic Virus. Worked with the Tobacco Mosaic Virus. Affects members of the tobacco family: white potatoes, tomatoes and garden peppers. Affects members of the tobacco family: white potatoes, tomatoes and garden peppers. Coined the term “virus,” it means “poison” Coined the term “virus,” it means “poison”

The Basics All organisms on Earth have at least one virus that affects them. All organisms on Earth have at least one virus that affects them. Viruses carry a piece of DNA or RNA from a living organism. Viruses carry a piece of DNA or RNA from a living organism. Pathogens: agents of disease. “that which produces suffering” Pathogens: agents of disease. “that which produces suffering” Viruses are not considered to be alive. Viruses are not considered to be alive.

The basics continued. Most viruses consist of DNA and a protein coat called a capsid. This is used to bind the virus to the host cell. Some have RNA and are called retroviruses. Most viruses consist of DNA and a protein coat called a capsid. This is used to bind the virus to the host cell. Some have RNA and are called retroviruses.

Viral Basics Viral Basics Many animal viruses also have a membrane, called an envelope, that they took from the last host as they were pushing out of the cell. It can be made from proteins, lipids, and glycoproteins. This allows them access to the new hosts cells. Many animal viruses also have a membrane, called an envelope, that they took from the last host as they were pushing out of the cell. It can be made from proteins, lipids, and glycoproteins. This allows them access to the new hosts cells.

Size Viruses range between 20 and 200 nanometers. Viruses range between 20 and 200 nanometers. They are barely able to be seen with our best light microscope. They are barely able to be seen with our best light microscope. Most are seen through the use of electron microscopes. (TEM and SEM) Most are seen through the use of electron microscopes. (TEM and SEM)

Shapes Helical shaped like the Tobacco Mosaic Virus. Helical shaped like the Tobacco Mosaic Virus. Polyhedral like the adenovirus which causes the common cold Polyhedral like the adenovirus which causes the common cold

Shapes Round like the influenza virus. Round like the influenza virus. Complicated injection structures like the Complicated injection structures like the T4 bacteriophage, “Bacteria eaters” T4 bacteriophage, “Bacteria eaters”

Reproduction No metabolic enzymes No metabolic enzymes No ribosomes, therefore, no equipment for protein synthesis. No ribosomes, therefore, no equipment for protein synthesis. MUST have a living cell to carry out their life cycle. “Hijackers” MUST have a living cell to carry out their life cycle. “Hijackers” Overwrites the cell blueprints, causes host cells to become “Virus Factory” Overwrites the cell blueprints, causes host cells to become “Virus Factory”

Entry methods Bacteriophage punches hole in bacteria and injects DNA. Bacteriophage punches hole in bacteria and injects DNA. Plant viruses enter through tiny holes/rips in the cell wall. Holes/rips usually due to injury to plant. Plant viruses enter through tiny holes/rips in the cell wall. Holes/rips usually due to injury to plant. Animal viruses enter through endocytosis. Cell is tricked into taking virus inside. Animal viruses enter through endocytosis. Cell is tricked into taking virus inside.

Animal virus specifics Very specific binding sites, like an enzyme lock and key system. Very specific binding sites, like an enzyme lock and key system. Only receptor sites that exactly match the virus glycoproteins will allow virus in: Only receptor sites that exactly match the virus glycoproteins will allow virus in: HIV…white blood cells HIV…white blood cells Polio…spinal nerve cells Polio…spinal nerve cells Hepatitis…liver cells Hepatitis…liver cells Meningitis…meninges of spinal column and brain cells Meningitis…meninges of spinal column and brain cells

Plant virus specifics Most plant viruses carry RNA, rather than DNA. Most plant viruses carry RNA, rather than DNA. Some are carried by insects that feed on the plants using piercing mouthparts. Some are carried by insects that feed on the plants using piercing mouthparts. Can cause severe damage to major cash crops. Can cause severe damage to major cash crops. Impatiens Necrotic Spot Virus (INSV) Impatiens Necrotic Spot Virus (INSV) Cucumber Mosaic Virus (CMV) Cucumber Mosaic Virus (CMV) Tomato Ringspot Virus (Tom RSV) Tomato Ringspot Virus (Tom RSV)

Viral Origins Fragments of host genomes. Fragments of host genomes. Incredible diversity due to so many templates available to escape from. Incredible diversity due to so many templates available to escape from. Coevolutionary partnership offers protection to species habitats. Coevolutionary partnership offers protection to species habitats. Viruses of nearly all the major classes of organisms - animals, plants, fungi and bacteria / archaea - probably evolved with their hosts in the seas, given that most of the evolution of life on this planet has occurred there. Viruses of nearly all the major classes of organisms - animals, plants, fungi and bacteria / archaea - probably evolved with their hosts in the seas, given that most of the evolution of life on this planet has occurred there.