Viruses

1. Viruses Biology: Kingdoms Research Project Mr. Jones EM of Enveloped Virus with receptor molecules

2. Viruses: Overview & Concepts • Structure • Adaptations • Reproduction & Development • Diversity • Phylogeny • Importance TEM: Ebola Virus

3. Definition: Virus • Sub microscopic entity consisting of a single nucleic acid (N.A) surrounded by a protein coat, or capsid, capable of replication only within a living host. • Obligate Intracellular Parasite

4. Are Viruses Alive? • Characteristics of life • What Viruses Don’t... • Respire (produce energy) • Metabolize (make biological molecules) • Grow & Develop • What Viruses Do... • Reproduce- obligate to a host • Adapt/Evolve- change through time

5. Viral Morphology (Structure) • Basic Structure: 2 principle structures • Protein Capsid • Outer covering protecting core & giving shape • Inner Nucleic Acid Core (RNA or DNA) • Used in viral classification • *Envelope or Lipoprotein Coat • Enveloped viruses- similar to their eukaryotic host cell’s plasma membrane • Not present in all viruses

6. Lipid Envelope Nucleic Acid Protein Capsid Virion Associated Polymerase (enzyme) Receptor Molecules Basic Enveloped Viral Structure Influenza Virus following lytic cycle

7. Structure: Capsid Protein Arrangement • Protein Arrangement Determines: • 1. Viral shape- images on next slide • Polyhedral (HPV, Polio, Adenovirus) • Helical (Tabacco Mosiac Virus) • Enveloped (Influenza, HIV) • Binal (baceriophages) • 2. What host a virus can infect • 3. Method virus will infect host

8. Typical Viral Shapes

9. Viral Size • Extremely Small... • most range 5nm-300nm • as small as ribosomes • between 4-900 genes • Yet Complex... • Icosahedrals like polio & adenoviruses can have up to 20 symmetrical sides Learn more in the Class Project Bacteriophages infect bacteria DYK?- 1 drop of blood can contain as many as 6 billion viruses!

10. Virus Classification • Classified by Shape & Nucleic Acid Class • DNA viruses – stable, do not mutate as rapidly • Single-stranded or double-stranded • Smallpox, Hepatitis B • RNA viruses – mutate rapidly, unstable • Single-stranded or double-stranded • HIV, Rhinovirus (common cold)

11. Viral Classification Chart

12. Naming Viruses • Once named by... • Common names such as... • Diseased they cause (rabies, poliovirus) • Organ or tissue they infect (adenovirus: from adenoid tissue where common cold is found) • Universal System(s) • Families with Genus name + “virus” & species name + “viridae” (herpesviridae)

13. Viral Adaptations Bacteriophases invading E.coli • Viruses evolve quickly • Have several methods of infecting a host • Viruses can survive for long periods of time both inside & outside of a host • Recognition & Attachment • Virus receptor molecule to cell receptor site • Viral species are specific to host • Smallpox- affects only humans • Polio- affects only certain human nerve cells

14. Viral Adaptations • Transmission • Air, fluids (blood, fecal, sexual), animal vectors (insects, mice, monkeys) • Methods of entering & leaving host • Direct attachment to receptor molecule (Polyhedral viruses) • Endocytosis with cell membrane (Enveloped viruses) • Attachment by tail fibers (Binal viruses)

15. Viral Reproduction • Reproductive Overview: A Virus... • infects a host through a reception mechanism • alters host ribosomes, DNA, or RNA • uses host metabolism to replicate N.A. • Host cell makes & assemble new viruses • Host cell lyses (burst) leading to cell death • All host cell’s eventually enter a Lytic Cycle

16. Viral Reproduction Diagram

17. Viral Diversity • There are 22 classes of bacteria. • 400 identified plant viruses causing up to 1,000 identified diseases • Eastimated: • 1000’s of animal viruses causing as many as 10,000 diseases • 1031 bacteriophages on Earth alone

18. Viral Diversity • Reproductive Cycles • Lytic & Lysogenic Cycles • Provirus • viral DNA integrated into host DNA • remains dormant or inactive • Retroviruses • contain enzyme reverse transcriptase • RNA is transcribed into DNA (ex. HIV)

19. Lytic Cycle • Virus attaches to host cell’s membrane and injects its nucleic acid into the host cell. • The viral nucleic acid takes over protein synthesis, creating new viruses. • The host cell lyses releasing the newly formed viruses. • Cycle repeats exponentially

20. Before attachment Attachment/Reception Penetration of N.A. Cell lyses Replication of viral proteins Viral assembly

21. Lysogenic Cycle • Viral N.A. are integrated into host’s DNA becoming a provirus • Provirus is replicated with host cell replication (mitosis) • Infect cell’s turn lytic, killing host cells • Lysogenic Cycle Video • http://www.youtube.com/watch?v=_J9-xKitsd0

22. Lysogenic Cycle

23. Lytic Kills host cells Mutates quickly & ramdomly Often without benefit to the virus Rapid Typical lytic cycle- 30 minutes to produce 200 viruses Lysogenic, Provirus, & Retrovirus Uses cell’s reproduction & lysis NA integration into cell DNA remain dormant for periods of time Slower High transmission rate Slower but more effective mutation Adaptations- Comparing Cycles

24. Viral Phylogeny • Viruses likely evolved from the host themselves • Some may have evolved in protists such as amoebas • HIV phylogeny & evolution • Emergent Viruses- host to human

25. HIV Phylogeny- SIV to HIV

26. Importance • Viruses drive evolution • Adapted organisms survive • Controls populations • Mutate genetics of host • Both for the good & bad • Gene Therapy & Viral Vectors • Using viruses to transmit healthy genes to people with genetic disorders & diseases

27. Importance • No Cure- most drugs affect enzymes, cell membranes, or reproductive cycle; virus have almost none of these traits • Vaccines & immunization • Cowpox & Smallpox (eradicated) • HIV can infect 10 billion cells per day, the body can only replace 1.8 • AIDS Prevalence • http://www.avert.org/worldstats.htm • http://kwanzaakeepers.com/africa-aids-death-count/africa-aids-death-count.htm • One sub-Saharan African is infected with HIV every 9 seconds. One person dies from AIDS every 13 seconds.