1 / 32

Chapter 13, part A

Chapter 13, part A. Viruses, Viroids, and Prions. Viruses. Viruses contain DNA or RNA And a protein coat Some are enclosed by an envelope Some viruses have spikes Most viruses infect only specific types of cells in one host

Download Presentation

Chapter 13, part A

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.


Presentation Transcript

  1. Chapter 13, part A Viruses, Viroids, and Prions

  2. Viruses • Viruses contain DNA or RNA • And a protein coat • Some are enclosed by an envelope • Some viruses have spikes • Most viruses infect only specific types of cells in one host • Host range is determined by specific host attachment sites and cellular factors

  3. Viruses versus cellular organisms Cellular Organisms • complex organization • both DNA and RNA • carry out cell division • some are obligate intracellular parasites Viruses • simple organization • DNA or RNA but not both (one exception) • unable to reproduce outside of living cells • obligate intracellular parasites

  4. Viruses Figure 13.1

  5. Helical Viruses Figure 13.4a, b

  6. Polyhedral Viruses Figure 13.2a, b

  7. Complex Viruses Figure 13.5a

  8. Viral Taxonomy • Family names end in -viridae • 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

  9. Viral Taxonomy • Herpesviridae • Herpesvirus • Human herpes virus 1, HHV 2, HHV 3 • Retroviridae • Lentivirus • Human Immunodeficiency Virus 1, HIV 2

  10. Growing Viruses • Viruses must be grown in living cells. • Bacteriophages form plaques on a lawn of bacteria. Figure 13.6

  11. The Cultivation of Viruses • requires inoculation of appropriate living host

  12. Hosts for animal viruses • suitable animals • embryonated eggs • tissue (cell) cultures • monolayers of animal cells • plaques • localized area of cellular destruction and lysis • cytopathic effects • microscopic or macroscopic degenerative changes or abnormalities in host cells and tissues

  13. Growing Viruses • Animal viruses may be grown in living animals or in embryonated eggs. Figure 13.7

  14. Growing Viruses • Animal and plants viruses may be grown in cell culture. • Continuous cell lines may be maintained indefinitely. Figure 13.8

  15. Virus Identification • Cytopathic effects • Serological tests • Detect antibodies against viruses in a patient • Use antibodies to identify viruses in neutralization tests, viral hemagglutination, and Western blot • Nucleic acids • RFLPs • PCR

  16. Hosts for bacteriophages • usually cultivated in broth or agar cultures of suitable, young, actively growing bacteria • broth cultures lose turbidity as viruses reproduce • plaques observed on agar cultures

  17. Multiplication of Bacteriophages (Lytic Cycle) • Attachment Phage attaches by tail fibers to host cell • Penetration Phage lysozyme opens cell wall, tail sheath contracts to force tail core and DNA into cell • Biosynthesis Production of phage DNA and proteins • Maturation Assembly of phage particles • Release Phage lysozyme breaks cell wall

  18. Bacterial cell wall Bacterial chromosome Capsid DNA Capsid Sheath Tail fiber Tail 1 Attachment:Phage attaches to host cell. Base plate Pin Cell wall Plasma membrane 2 Penetration:Phage penetrates host cell and injects its DNA. Sheath contracted Tail core 3 Biosynthesis: DNA and Protein Figure 13.10.1

  19. Tail DNA 4 Maturation:Viral components are assembled into virions. Capsid 5 Release:Host cell lyses and new virions are released. Tail fibers Figure 13.10.2

  20. One-step Growth Curve Figure 13.11

  21. Lytic cycle Phage causes lysis and death of host cell • Lysogenic cycle Prophage DNA incorporated in host DNA

  22. The Lysogenic Cycle Figure 13.12

  23. Specialized Transduction gal gene Bacterial DNA Prophage 1 Prophage exists in galactose-using host (containing the gal gene). Galactose-positive donor cell gal gene 2 Phage genome excises, carrying with it the adjacent gal gene from the host. 3 Phage matures and cell lyses, releasing phage carrying gal gene. gal gene 4 Phage infects a cell that cannot utilize galactose (lacking gal gene). Galactose-negative recipient cell 5 Along with the prophage, the bacterial gal gene becomes integrated into the new host’s DNA. 6 Lysogenic cell can now metabolize galactose. Galactose-positive recombinant cell Figure 13.13

  24. Multiplication of Animal viruses • Attachment Viruses attaches to cell membrane • Penetration By endocytosis or fusion • Uncoating By viral or host enzymes • Biosynthesis Production of nucleic acid and proteins • Maturation Nucleic acid and capsid proteins assemble • Release By budding (enveloped viruses) or rupture

  25. Virus Purification and Assays • development of virology closely linked to development of these methods

  26. Virus Purification • four commonly used methods • differential centrifugation and density gradient centrifugation • precipitation of viruses • denaturation of contaminants • enzymatic digestion of cell constituents

  27. Differential centrifugation • separates based • on size

  28. Density gradient centrifugation

  29. Measuring concentration of infectious units • plaque assays • dilutions of virus preparation made and plated on lawn of host cells • number of plaques counted • results expressed as plaque-forming units (PFU)

  30. Measuring concentration of infectious units… • infectious dose and lethal dose assays • determine smallest amount of virus needed to cause infection or death of 50% of exposed host cells or organisms • results expressed as ID50 or LD50

  31. Graph

More Related