 Viruses are small infectious agents  They are so small that they can only be seen with a very powerful electron microscope Ebola Virus under electron microscope Swine Flu Virus under electron microscope

 Viruses are highly specific to the cells they infect  Viruses that infect bacteria are called bacteriophages  A retrovirus is a virus that contains RNA rather than DNA  A virus can reproduce only by infecting living cells; Once they infect a cell, they use that cell’s “materials” to produce more viruses

 A typical virus is composed of a core of DNA or RNA (nucleic acids) surrounded by a protein coat (capsid)  Viruses come in a wide variety of shapes and sizes  The capsid contains proteins that allow a virus to bind to a cell and “trick” the cell into allowing it inside

DNA or RNA Capsid BODY

 With your partner, explain whether a virus is living or non-living (think back to the characteristics of life).  Time: 1 minute

 Viruses are considered NON-LIVING  WHY? › They are not made up of cells › They are not capable of living independently (require a host cell) › They do not grow and develop › They do not obtain and use energy › They do not respond to their environment

 Once a virus is INSIDE the host cell, two different things can occur › LYTIC INFECTION : The virus immediately makes copies of itself and causes the cell to burst (releasing the replicated viruses) › LYSOGENIC INFECTION: The virus intertwines its DNA with the host DNA, but lies dormant for a period of time. In a sense it “hides out” until it is ready to enter the lytic stage