VIRUSES

What is a VIRUS? 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

What is a VIRUS? 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

Parts of a Virus 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

Check for Understanding

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

Time: 1 minute

Living or Non-Living?

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

Viral Infection

Viral Infection/Reproduction

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