Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 10.22

Viruses 1.Components 2.Infection cycle 3. DNA, RNA viruses 4. Uses of viruses VIRUSES: GENES IN PACKAGES

Components of a virus (phage) 1. Protein coat = capsid 2.genetic material DNA or RNA 3. enzyme

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Components of a virus Figure 10.18A Membranous envelope RNA Protein coat Glycoprotein spike envelope capsid genetic material –Ex. flu viruses

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Phage reproductive cycle Phage attaches to bacterial cell. Phage injects DNA. Phage DNA directs host cell to make more phage DNA and protein parts. New phages assemble. Cell lyses and releases new phages.

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Viral DNA may become part of the host chromosome Phage New phage DNA and proteins are synthesized Phage DNA inserts into the bacterial chromosome by recombination Attaches to cell Phage DNA Bacterial chromosome Phage injects DNA Occasionally a prophage may leave the bacterial chromosome Many cell divisions Lysogenic bacterium reproduces normally, replicating the prophage at each cell division Prophage Phage DNA circularizes LYSOGENIC CYCLE Cell lyses, releasing phages Phages assemble LYTIC CYCLE OR

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Viruses redirect the host cell machinery to make more viruses Some animal viruses steal a bit of the host cell’s membrane Figure 10.18B VIRUS Glycoprotein spike Protein coat Envelope Viral RNA (genome) 1 Plasma membrane of host cell Entry 2 Uncoating Viral RNA (genome) 3 RNA synthesis by viral enzyme 4 Protein synthesis 5 RNA synthesis (other strand) mRNA New viral protein New viral proteins 6 Assembly 7 Exit Template New viral genome

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Most plant viruses have RNA –Example: tobacco mosaic disease Plant viruses are serious agricultural pests Figure ProteinRNA

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The deadly Ebola virus causes hemorrhagic fever –Each virus is an enveloped thread of protein-coated RNA Hantavirus is another enveloped RNA virus SARS - coronavirus Avian flu Figure 10.20A, B

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings –HIV, seen here attacking a white blood cell Figure 10.22

HIV is a retrovirus

Invasion of T cell by HIV

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings HIV infection Figure 10.22x1

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings AIDS quilt Figure 10.22x2

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Uses of Viruses Pest control Vaccines Anti-cancer treatment Gene therapy

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Anti-cancer viruses Makes use of viral ability to enter only cells of one type Allows targeting of therapy to tumor cells Enables identification of small tumor sites

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Coming soon to your local pharmacy!

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Other parasitic particles Viroids - infectious RNA (no capsid) Prions - infectious protein –Cellular PrP, prion PrP –Spongiform encephalopathies cause neural degeneration