VIRUSES Text p.104-107 http://www.ted.com/talks/nathan_wolfe_what_s_left_to_explore?language=en

Cause many diseases

Are parasites that infect living cells When a virus attacks, it shows signs of being alive Can reproduce Has biological molecules: protein coat and nucleic acids (DNA, RNA) HIV Influenza virus ebola virus

But viruses are not alive Not cells, have no organelles No metabolism, does not use ATP Do not grow, have no chemical reactions Much smaller than any cell 1/10 the volume of a small bacteria 0.03 to 0.3 μm (10 to 100 x smaller than bacteria) http://www.dnatube.com/video/12206/Size-Analogies-of-Bacteria-and-Viruses Each virus attacks only a specific type of cell eg. Plant, animal, bacteria A virus that infects bacteria is called a bacteriophage (“phage” = to eat) Discovered with the invention of the electron microscope

Bacteriophage

VIRAL REPLICATION

VIRAL REPLICATION 2 Types of processes Lytic Cycle: has 4 steps Attachment: Virus recognizes host cell Virus attaches to it Injects whole virus or just DNA or RNA

Synthesis: Viral DNA or RNA instruct the cell to produce new virus parts Assembly: New virus parts are brought together and assembled into new viruses

Lytic cycle may be completed in only 25-45 minutes Release: New viruses are released from the infected cell & the cell dies Lytic cycle may be completed in only 25-45 minutes Hundreds of new viruses produced!

The Lytic Cycle

VIRAL REPLICATION Lysogenic Cyle In this cycle, the virus goes into a dormant stage (“sleeping”) Virus injects its DNA or RNA into the host cell, but it does not take control of the host cell Instead, the viral DNA becomes part of the cell’s DNA It is reproduced as the cell is reproduced  all daughter cells contain the virus The host cell does not die

The Lysogenic Cycle

At some point, as a result of some stimulation, the virus can be triggered to re-enter the lytic cycle Eg. Stress like pregnancy, serious illness, surgery, psychological stress