1. VIRUSES NONLIVING PARTICLES

2. Viruses  Smaller than bacteria  Known since late 1800’s but no way to study them  1935 Tobacco mosaic virus was crystallized  1 st time scientists suspected virus chemical and not living

3. WHAT IS A VIRUS?  PARTICLES OF NUCLEIC ACIDS, PROTEINS AND IN SOME CASES LIPIDS THAT CAN REPRODUCE ONLY BY INFECTING LIVING CELLS.

4. Virus Structure (bacteriophage)

5. Helical Virus Structure

6. Icosahedral Virus Structure(polio)

7. HOW VIRUSES WORK  ONCE INSIDE OF LIVING CELLS, VIRUSES USE THE MACHINERY (NUCLEIC ACIDS) OF THE INFECTED CELL TO PRODUCE MORE VIRUSES.

8. TYPICAL VIRUS STRUCTURE  MADE OF A CORE OF EITHER DNA OR RNA SURROUNDED BY THE CAPSID - A PROTEIN COAT

9. Envelope  Membrane-like structure outside of the capsid;  Made mostly of lipids;  Taken from a host cell membrane during replication;  Allows new viruses to infect host cells during 1 st stage of viral infection;

10. Envelope  Glycoproteins – projections of protein-containing sugar chains that a virus uses to attach to a host cell.

11. Viruses that have an envelope  Influenza  Chickenpox  Herpes simplex  HIV

12. THE SHAPES OF VIRUSES

13. VIRUSES ARE SPECIFIC  VIRUSES BIND PRECISELY TO PROTEINS ON THE CELL SURFACE  THE CAPSID INCLUDES PROTEINS THAT TRICK THE CELL INTO ALLOWING IT INSIDE

14. GROUPING VIRUSES  BASED ON PRESENCE OF CAPSID & ENVELOPE, IF THEY CONTAIN RNA OR DNA AND IF NUCLEIC ACID IS SINGLE OR DOUBLE-STRANDED;  TABLE 25-2, PAGE 489, LISTS COMMON VIRUSES OF HUMANS AND THEY ARE GROUPED;

15. VOCABULARY FOR UNDERSTANDING  BACTERIOPHAGE – VIRUSES THAT INFECT BACTERIA;  PROPHAGE – INTRACELLULAR B.PHAGE THAT IS HARMLESS TO THE HOST CELL;

16. VIRAL INFECTION  LYTIC INFECTION – A VIRUS INVADES A HOST CELL, PRODUCES NEW VIRUSES, DESTROYS THE HOST CELL & RELEASES THE VIRUSES

17. LYTIC INFECTION  LYTIC VIRUSES ARE VIRULENT – DEGREE OF PATHOGENICITY OF A MICROBE;  VIRULENT (L) – “FULL OF POISON”  INFLUENZA; POLIO  A SINGLE VIRUS CAN INFECT A CELL AND PRODUCE 100 VIRUS PARTICLES IN 20 MINUTES

18. LYTIC CYCLE STAGES  BACTERIOPHAGE ATTACHES TO CELL AT A RECEPTOR SITE;  B. PHAGE RELEASES AN ENZYME THAT WEAKENS A SPOT IN CELL WALL OF HOST;  B. PHAGE INJECTS DNA INTO THE HOST CELL;  VIRUS TAKES CONTROL OF HOST’S DNA;

19. LYTIC CYCLE  VIRUS TRANSCRIBES MESSENGER RNA FROM THE VIRUS’ DNA;  THE M. RNA IS TRANSLATED INTO PROTEINS THAT FORM B. PHAGE CAPSIDS CONTAINING THE VIRUS  AN ENZYME CAUSES THE HOST CELL TO LYSE (BURST) RELEASING THE NEW BACTERIOPHAGES.

20. VIRAL INFECTION  LYSOGENIC CYCLE:  TEMPERATE VIRUSES – DON’T KILL HOST IMMEDIATELY;  BACTERIOPHAGE;  PROPHAGE;  HIV A LYSOGENIC VIRUS;

21. LYSOGENIC CYCLE  B. PHAGES ATTACH TO A RECEPTOR SITE, RELEASE AN ENZYME THAT WEAKENS CELL WALL OF HOST AND INJECTS DNA.  DNA INTEGRATES ITSELF INTO THE HOST CELL’S DNA

22. LYSOGENIC CYCLE  B. PHAGE DOES NOT IMMEDIATELY CREATE NEW RNA AND VIRAL PROTEINS;  B. PHAGE DNA MOLECULE INTEGRATES ITSELF INTO A SPECIFIC SITE OF THE HOST CELL’S GENOME – THE PROPHAGE.

23. LYSOGENIC CYCLE  PROPHAGE REPLICATES WHENEVER THE HOST BACTERIUM REPRODUCES;  EACH BACTERIAL OFFSPRING IS INFECTED WITH A PROPHAGE;  AT SOME POINT, PROPHAGE BECOMES VIRULENT, ENTERS LYTIC CYCLE, MAKING M. RNA & DESTROYING HOST CELL.

24. VIRUS PREVENTION  VACCINE-PREPARATION OF A WEAKENED OR KILLED VIRUS OR VIRAL PROTEINS THAT STIMULATES THE IMMUNE SYSTEM PRODUCING IMMUNITY AGAINST THE VIRAL DISEASE.

25. Types of Virus Vaccines  Inactivated viruses – do not replicate in a host system;  Attenuated viruses – genetically altered so they are incapable of causing disease under normal circumstances;  Protection is greater and lasts longer with vaccine from attenuated viruses;

26. Prevention/Treatment  Antiviral drugs – interfere with viral nucleic acid synthesis;  Very few antiviral drugs exist;  Acyclovir – herpes simplex  Azidothymidine – inhibits reverse transcriptase of retroviruses  Protease inhibitors – interferes with synthesis of viral capsids during viral replication

27. Emerging Viruses  Ebola – hemorrhagic virus; rapid death.  Hantavirus – affects lungs which fill with fluid; western U.S.  Machupo virus – S. America; “Black Typhus” – hemorrhagic, high fever, pain, rapid death.  Lassa fever virus – West Africa; hemorrhagic virus; zoonotic – from multimammate rat; 1-4 weeks duration

28. RETROVIRUSES  VIRUSES THAT CONTAIN RNA AS THEIR GENETIC INFORMATION –  RNA IS USED AS A TEMPLATE TO MAKE DNA.  AIDS IS A RETROVIRUS

29. PRIONS  PROTEIN INFECTIOUS PARTICLES  ABNORMAL FORMS OF PROTEIN THAT CLUMP TOGETHER IN A CELL  EVENTUALLY KILLS THE CELL  CONTAIN NO DNA OR RNA, ONLY PROTEIN;

30. Prions may cause  Mad cow disease (bovine spongioform encephalopathy)  CruetzFeld-Jakob disease  Scrapies (sheep)