Viruses

Viruses

1. CHARACTERISTICS OF VIRUSES VIRUSES

2. A virus is an infectious agent made up of nucleic acid ( DNA or RNA ) wrapped in a protein coat called a capsid . Viruses have no nucleus , no organelles , no cytoplasm or cell membrane— Non-cellular vs This is why it does NOT belong to any kingdom .

3. Are Viruses Living or Non-living? Biologists consider viruses to be non-living because: Are not cells Do not grow or respond to their surroundings Cannot make food, take in food, or produce wastes Viruses do not respond to stimuli. They can only multiply if in another living cell

4. Viruses have either DNA or RNA but NOT both. Viruses with RNA that transcribe into DNA are called retroviruses . HIV Infected Cell A flea is a parasite to a dog and is harmful to the dog. Viruses are parasites — an organism that depends entirely upon another living organism (a host ) for its existence in such a way that it harms that organism.

5. What are Viruses? Definition- Viruses are non-cellular particles made up of genetic material and protein that can invade living cells.

6. Discovery of Viruses Beijerinck (1897) coined the Latin name “ virus ” meaning poison Ivanovski and Beijerinck

7. Tobacco Mosaic Virus Wendell Stanley (1935) discovered viruses were made of nucleic acid and protein

8. Smallpox Edward Jenner (1796) developed a smallpox vaccine using milder cowpox viruses Smallpox has been eradicated in the world today

9. How Big is a Virus? Viruses are very small – smaller than the smallest cell . Porcine circovirus type 1 has a capsid diameter of only 17nm i.e. 0.017µm Mimivirus : Protein filaments measuring 100 nm project from the surface of the capsid, bringing the total length of the virus up to 600nm (0.6µm) and a capsid diameter of 400nm (0.4µm). It is the third-largest virus, preceded by the recently discovered Megavirus chilensis and Pandoravirus .

10. Characteristics Non living structures Non-cellular Contain a protein coat called the capsid Have a nucleic acid core containing DNA or RNA (one or the other - not both) Capable of replication only when inside a HOST cell Exist in two distinct states: a virus (when active) and a virion (when dormant and not in contact with a host cell). Can also remain dormant within an organism (latency). A viriod (NOT VIRION) is an infectious RNA particle that resembles a virus – but is smaller .

11. Prions has protein only, no DNA or RNA (cause of mad cow disease and Creutfeldt -Jacob disease in humans)—affects the brain and is always fatal No DNA or RNA! Prions are made up of harmless proteins that are found in mammals and birds. But these proteins are in abnormal form and once they enter human brain, they are capable of severe brain infections. Normally these prions are ingested but they also get formed through mutation of a gene that contains this protein.

12. Characteristics Some viruses are enclosed in an protective envelope Some viruses may have spikes to help attach to the host cell Most viruses infect only SPECIFIC host cells CAPSID ENVELOPE DNA SPIKES

13. Cert ain viruses can only attack certain cell types. They are said to be specific . It’s like the pieces of a puzzle. The ends have to match up so only certain pieces fit. Surface Markers Receptor Sites Example: The rabies virus only attacks brain or nervous cells. Virus Cell

14. Surface Markers Receptor Sites Virus A virus recognizes cells it can infect by matching its surface marker with a receptor site on a cell. Cell

15. Outside of host cells, viruses are inactive Viruses cause many common illnesses/ diseases Some viruses may cause some cancers like leukemia EBOLA VIRUS HIV VIRUS MEASLES

16. What do Viruses look like? Viruses are unusual and different from other things in nature. Viruses come in a variety of shapes Some may be helical shape like the Ebola virus Some may be polyhedral shapes like the influenza virus Others have more complex shapes like bacteriophages

17. Viruses: Structure Viruses can have different shapes: Polyhedral cubical e.g. adenovirus Helical spiral cylinder e.g. tobacco virus Complex tadpole-like e.g. bacteriophage

18. Types of Viruses: Helical Viruses

19. Polyhedral Viruses

20. Complex Viruses

21. Viruses can be placed in one of the seven following groups: I: dsDNA viruses (e.g. Adenoviruses, Herpesviruses, Poxviruses) II: ssDNA viruses (+)sense DNA (e.g. Parvoviruses) III: dsRNA viruses (e.g. Reoviruses ) IV: (+) ssRNA viruses (+)sense RNA (e.g. Picornaviruses, Togaviruses ) V: (−) ssRNA viruses (−)sense RNA (e.g. Orthomyxoviruses , Rhabdoviruses ) VI: ssRNA -RT viruses (+)sense RNA with DNA intermediate in life-cycle (e.g. Retroviruses) VII: dsDNA-RT viruses (e.g. Hepadnaviruses and Caulimoviridae )

22. R

23. Viral Taxonomy Order names end in - virales Family names end in – viridae Subfamily - virinae Genus names end in - virus Viral Species: A group of viruses sharing the same genetic information and ecological niche (host). Common names are used for species Subspecies are designated by a number

24. Herpes Virus SIMPLEX I and II

25. Adenovirus COMMON COLD

26. Influenza Virus

27. Papillomavirus – Warts!

28. HOST SPECIFICITY All kingdoms can be infected by viruses Viruses are kingdom specific but they may or may not be species specific Spread is specific to the type of virus

29. PARASITISM Viruses are parasites. i.e. it depends upon another living organism for its existence in such a way that it harms that organism.

30. Viral Replication

31. Capsid Nucleic Acid Bacteriophage—a virus that infects bacteria (bacteria is the host)

32. Capsid ( protein coat) inside contains either RNA or DNA Bacteriophage — viruses that infect bacteria

33. Viruses: Life Cycle 1) Adsorption Virus approaches a cell. 2) Penetration Virus attaches to the cell, injecting nucleic acid into the cell. Capsid left outside cell. 3) Latent phase Virus multiplies its nucleic acid using materials from the host cell. 4) Lysis Protein coats form around strands of nucleic acid. The cell releases viruses.

34. Lytic Cycle

35. Lysogenic Cycle All phage species can undergo a lytic cycle Phages capable of only the lytic cycle are called virulent The alternative to the lytic cycle is called the lysogenic cycle: no progeny particles are produced, the infected bacterium survives, and a phage DNA is transmitted to each bacterial progeny cell when the cell divides Those phages that are also capable of the lysogenic cycle are called temperate

36. Lysogenic Cycle

37. Cylces Lysogenic Cycle Viral DNA May stay inactive in host for long periods of time Long lasting Example Mono or chickenpox Lytic Cylce Short and can be over come Example flu virus

38. Viruses: Effects on Body Host cells are affected in three ways: The host cells may be destroyed. They may swell and burst, e.g. as with nerve cells infected with the rabies virus. The host cells may not be able to function correctly, e.g. ciliated epithelial cells infected with the influenza virus. The virus can interact with the host cell’s chromosomes causing a mutation, e.g. warts and cancer cells. The immune system becomes activated in order to fight the infection. This may lead to fever, tiredness or an opportunistic disease.

39. Vaccine Is a weaken form of the virus To expose your immune system to the virus which will allow your body to better fight off the virus when exposed to the full blow virus.

40. Virus Living Cell RNA or DNA core (center), protein coat ( capsid ) Copies itself only inside host cell--REPLICATION DNA or RNA NO NO NO NO Cell membrane, cytoplasm, genetic material, organelles Asexual or Sexual DNA and RNA YES—Multicellular Organisms YES YES YES Structure Reproduction Genetic Material Growth and Development Response to Environment Change over time Obtain and Use Energy

41. How many characteristics of life do viruses possess? ONE *Genetic Material Are viruses living? NO

42. Assignment 1 Describe the life cycle of a temperate phage with a labelled diagram. Compare viruses, virions , viroids and prions.