Viruses

1. Viruses Kathy Huschle Northland Community & Technical College

2. General Characteristics of Viruses • acellular, non-living agents • capable of infecting all forms of life • Bacteria • Archaea • Eukarya Dengue virus

3. General Characteristics of Viruses • viruses that infect bacteria are called bacteriophage or phage • have been studied extensively due to the fact that they can be cultivated easily in bacteria and bacteria multiply rapidly • the knowledge gained from the study of phage has contributed greatly to the study of viruses that infect plants and animals a – cell fragment b – capsid with DNA c - capsid no DNA d – collar e – sheath f - core

4. T2 Phage

5. General Characteristics of Viruses • animal viruses infect only animals • plant viruses infect only plants • infected animals or plants are referred to as hosts for the viruses

6. General Characteristics of Viruses • viruses are incapable of • metabolism • growth • reproduction

7. General Characteristics of Viruses • to accomplish any of the above, a virus must invade a living host • because of the necessity of invading a living host to multiply, viruses have been referred to as obligatory intracellular parasites

8. General Characteristics of Viruses • viral size • range in size from 10 nm to 500 nm

9. General Characteristics of Viruses • virus has specificity for a host cell • host cell must be permissive and compatible in order for the virus to be able to enter

10. General Characteristics of Viruses • viruses exist in 2 phases 1. metabolically inert • outside of the living cell 2. replication form • found inside host cells

11. Virus Architecture • the virus particle consists of • nucleic acid, either DNA or RNA • viral genome • capsid • a protein coat surrounding the nucleic acid • nucleocapsid • nucleic acid and capsid combined

12. Viral Architecture • viruses come in various shape • isometric shape • appear spherical under an electron microscope

13. Virus Architecture • helical shape • filimentous or rodlike appearance

14. Virus Architecture • complex shape • most common shape for phage • isometric head with a sheath or tail

15. Virus Architecture • viruses consist of two basic types • naked virus • protein capsid is the outer layer of the virus • most common type of virus

16. Virus Architecture • enveloped virus • matrix protein surrounds the nucleocapsid • this matrix is then enclosed in an envelope • spikes project from the envelope and are used for attachment to the host cell enveloped Norwalk Virus

17. Virus Replication • viruses can only multiply in living cells that are actively metabolizing • virus nucleic acid directs the formation of new viral protein and nucleic acid • shuts down the host cell reproduction

18. Stages of Replicationof Phage 1. adsorption/attachment • virus attaches to outer surface of permissive host cell • protein in tail fibers attach to specific receptors on host

19. 2. penetration enzyme on the tail of the phage degrades the cell wall nucleic acid genome crosses plasma membrane passes through open channel in tail Phage Replication

20. 3. transcription phage DNA is transcribed to mRNA mRNA is then translated into phage proteins Phage Replication

21. Phage Replication • one of the first phage induced proteins produced is responsible for the degradation of the host cell DNA • as a result the host cell cannot transcribe DNA • this allows the phage DNA to take over the metabolism of the host cell for it’s own needs

22. Phage Replication 4. replication • phage DNA and protein replicate within the host cell independently of each other

23. 5. assembly or maturation phage DNA is packaged in the phage protein capsid fairly complex process Phage Replication

24. 6. release prior to release, the phage induce the synthesis of the enzyme lysozyme this enzyme degrades the cell wall internally, causing lysis of the cell assembled viruses are able to leave the host host cell is killed Phage Replication

25. Burst Size • burst size • average number of infectious viral units present when cell lyses or bursts • number ranges from 50 to 200

26. Viral Replication

27. Viral Replication Click the icons in order to review the stages of viral replication

28. Viral Replication

29. Virus Interaction • viruses interact in various ways with their host cell • complete take-over of cell metabolism resulting in lysis of the cell • sharing of cell metabolism • host cell continues to multiply while viruses “leak” out of the cell without destroying the cell • co-exist • multiply as the host cell multiplies

30. Virus Interaction • how the cell is affected by phage is determined by the type of phage • disease of the host cell • productive infection - lytic • infection where more phage are produced • phage multiply inside cell and are released from the cell due to lysis of the cell wall • these phage are referred to as lytic

31. Virus Interaction • disease of the host cell • productive infection - extruded • phage multiply within the host but do not kill the host cell • phage only partially take over the metabolism of the host • phage leak out of the host without killing the host

32. Virus Interaction • genetic alteration of host cell • temperate phage • integrate their DNA with host DNA • results in a latent infection • no symptoms

33. Virus Interaction temperate phage lytic phage

34. Host Range of Phage • host range is defined as the number of bacteria that a phage can infect • has been determined that this number is usually limited to one • factors that limit the host range of phage include • specific receptor sites • restriction-modification system

35. Host Range of Phage • specific receptor sites • vary in chemical structure or location

36. Host Range of Phage • restriction-modification system • restriction enzymes recognize sequences of DNA and degrade the DNA at that site • this can be viral DNA also • modification enzymes add methyl groups to bases to prevent recognition • use this method to protect their own DNA from degradation Thermophile infected by a virus

37. Infectious Agents of Animals and Plants

38. Animal Viruses • basic biology similar to bacteriophage • nucleocapsid: either RNA or DNA surrounded by a protein coat • naked virus: no additional covering • enveloped virus: membrane surrounds nucleocapsid • most animal viruses are enveloped • rarely found in plant or bacterial viruses Filovirus

39. Animal Virus Shapes • there are no complex tailed forms of animal or plant viruses` pleomorphic: irregular shape helical isometric rhabdovirus Ebola virus

40. Human viruses are grouped based on transmission routes

41. Studying Animal Viruses • studying animal viruses is more expensive and more time consuming than the study of bacterial viruses • since viruses multiply inside a living cell, that is where they must be studied • an animal cell cycle is not nearly as rapid as that of a bacterial cell • acquiring enough viruses to study is the challenge to studying animal viruses

42. Studying Animal Viruses • some viruses can only be grown in living animals • there is an ethical issue regarding purposely infecting an animal with a virus just for study • other viruses can be cultivated in tissue culture • this technique involves small pieces of tissue being removed from the animal and nurtured in the lab as a growth media for the virus

43. Studying Animal Viruses • animal viruses are also studied quantitatively by using • electron microscopy • actual counting of the viruses • agglutination • some viruses can clump red blood cells and the concentration can be measured based on this

44. Replication Cycle of Animal Viruses • animal virus reproduction can be compared with reproduction of bacteriophage with a few additional steps 1. attachment 2. entry : the entire virus enters the host cell 3. targeting (usually the nucleus) 4. uncoating: the nucleic acid separates from the capsid 5. replication of nucleic acid and protein 6. maturation

45. Replication Cycle of Animal Viruses 7. release • host cells often die due to lack of functioning DNA and the ability to function as needed. Cells lyse when they die, releasing the viruses. • budding is a process of releasing the virus that does not necessarily kill the host cell 8. shedding outside of host • usually use the same openings or surfaces used to gain entrance into the host 9. transmission to next host • enters the new host and the infection cycle begins again

46. Interactions of Animal Viruses with Hosts • outcome of viral infection is dependent on defense mechanisms of the host • state of the immune system in humans

47. Interactions of Animal Viruses with Hosts • if viral infection results in death, the virus can no longer spread • this is not a desirable situation for the virus Rhinovirus STD virus Corona virus

48. Interactions of Animal Viruses with Hosts • many viruses develop a relationship with their host that causes no harm or disease • this is called balanced pathogenicity • this balancing act can change if • the immune system is compromised • the virus is transmitted to an animal that has no immunity

49. Interactions of Animal Viruses with Hosts • relationship between disease causing viruses and their hosts can be • acute infections • persistent

50. Interactions of Animal Viruses with Hosts • acute infection • short duration of illness • generally develop a long-lasting immunity • productive infections • infected cells die • may or may not cause lysis