Discovery of Viruses

Name______Hour______Date______1

20.1 Viruses Discovery of Viruses o In 1892, Dmitri Ivanovski--found in the liquid extracted from ______.

o In 1897, Martinus Beijerinck- named tiny particles in the juice viruses-“______.”

o In 1935, Wendell Stanley- found crystals of tobacco mosaic virus. Since living organisms do not crystallize- viruses were ______Discovery of Viruses A virus is a nonliving particle made of  ______ ______ sometimes lipids.  Viruses can reproduce only by infecting ______Structure and Composition o Viruses differ widely in terms of ______&______

o Most viruses are so small they can be seen only with the aid of a powerful ______Structure and Composition o The protein coat surrounding a virus-______o May have an additional membrane that surrounds the capsid (______) o Contain a few genes to ______of genes Structure and Composition o Most viruses’ proteins on the surface membrane binds to ______on the host cell. o The proteins “______” the cell to take the virus or some genetic material o Once inside, genes are ______& may destroy the cell. Structure and Composition o Most viruses infect only a very ______kind of cell. o Plant viruses infect ______o Animal viruses infect only certain ______of animals o Viruses that infect bacteria are called ______Lytic Infections virus enters a ______makes ______of itself causes cell to burst- ______EX.) ______core inside ______capsid Name______Hour______Date______2

Lytic Infections 1.) ______2.) Injection: The virus injects its ______into host cell. 3.) Synthesis: Virus DNA uses host DNA to make more ______4.) Assembly: Host cell creates more of the viruses 5.) Releases: Finally the host cell ______(ruptures) hundreds of viruses that go on & ______other cells. Relate the Virus to an Outlaw in Wild West ______Lysogenic Infection  Some Viruses cause a ______infection. o ______state  ______-DNA that is embedded in the host’s DNA  The prophage may remain part of the DNA of the host cell for many______.  Influences from the environment—radiation, heat, etc—______the prophage to become active. o becomes an ______infection. A Closer Look at Two RNA Viruses o About ______of viruses contain______rather than DNA. o In humans, ______viruses cause a wide range of infections . mild ______to severe ______o Certain kinds of ______also begin with an infection by viral RNA. . HPV The Common Cold  Cold viruses attack with a very simple, fast-acting ______.  A capsid settles on a cell o typically in the ______ brought inside  Virus makes many new copies of the viral ______. The Common Cold o The host cell’s ______mistake the viral RNA for its ______& makes other virus proteins. o The new capsids assemble & within 8 hours, the host cell releases ______of new ______particles to infect other cells.

HIV  Acquired immune deficiency syndrome ______is caused by an RNA virus called human immunodeficiency virus ______.

 HIV belongs to a group of RNA viruses-______Name______Hour______Date______3

 The genetic information of a retrovirus is copied from ______to ______instead of from ______to ______. HIV  When a retrovirus infects a cell, it makes ______copy of its ______.  The copy inserts itself into the DNA of the ______cell. HIV  Retroviral infections are similar to ______infections of bacteria.  like a ______in a bacterial host, the viral DNA may remain inactive for many cell cycles before making new virus particles  HIV damages the host’s ______Viruses and Cells  All viruses are ______.  Parasites depend upon other living organisms for their existence  Viruses infect living cells in order to ______& ______ taking advantage of the nutrients & cellular machinery Viruses and Cells o Viruses have many of the characteristics of______.

o After infecting living cells, viruses can reproduce, regulate gene expression, & even ______. Viruses and Cells Summarize some main differences between Viruses and Cells