Viruses, viroids, and prions
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Viruses are non-living particles that can only replicate inside host cells. They contain genetic material surrounded by a protein coat. While viruses exhibit some properties of life, such as the ability to evolve, they cannot perform all biological functions or maintain homeostasis. Viruses come in a variety of shapes and sizes and infect organisms as diverse as plants, animals, bacteria and archaea. They are classified according to their nucleic acid composition and structure. Viruses either enter a dormant latent stage within the host cell or undergo lytic replication, which results in host cell death. Treatment options for viral diseases include vaccines containing weakened live or killed viruses, interferons, antiviral drugs that target specific virus functions, and genetic engineering of attenuated viruses
Viruses, viroids, and prions
- 2. 2 Are Viruses Living orAre Viruses Living or Non-living?Non-living? Viruses are both and neither They have some properties of life but not others For example, viruses can be killed, even crystallized like table salt However, they can’t maintain a constant internal state (homeostasis). copyright cmassengale
- 3. 3 What are Viruses?What are Viruses? A virus is a non- cellular particle made up of genetic material and protein that can invade living cells. copyright cmassengale
- 5. 5 Discovery of VirusesDiscovery of Viruses Beijerinck (1897) coined the Latin name “virus” meaning poison He studied filtered plant juices & found they caused healthy plants to become sick copyright cmassengale
- 6. 6 Tobacco Mosaic VirusTobacco Mosaic Virus Wendell Stanley (1935) crystallized sap from sick tobacco plants He discovered viruses were made of nucleic acid and protein copyright cmassengale
- 7. 7 SmallpoxSmallpox Edward Jenner (1796) developed a smallpox vaccine using milder cowpox viruses Deadly viruses are said to be virulent Smallpox has been eradicated in the world today copyright cmassengale
- 8. 8 Viewing VirusesViewing Viruses Viruses areViruses are smallersmaller than the smallest cellthan the smallest cell Measured inMeasured in nanometersnanometers Viruses couldn’t beViruses couldn’t be seen until theseen until the electronelectron microscopemicroscope waswas invented in theinvented in the 2020thth centurycentury copyright cmassengale
- 9. 9 Size of VirusesSize of Viruses copyright cmassengale
- 11. 11 CharacteristicsCharacteristics Non living structures Noncellular Contain a protein coat called the capsid Have a nucleic acid core containing DNA or RNA Capable of reproducing only when inside a HOST cell copyright cmassengale
- 12. 12 CharacteristicsCharacteristics 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 copyright cmassengale
- 13. 13 CharacteristicsCharacteristics Viral capsids (coats) are made of individual protein subunits Individual subunits are called capsomeres CAPSOMERES copyright cmassengale
- 14. 14 CharacteristicsCharacteristics Outside of host cells, viruses are inactive Lack ribosomes and enzymes needed for metabolism Use the raw materials and enzymes of the host cell to be able to reproduce EBOLA VIRUS HIV VIRUS copyright cmassengale
- 15. 15 CharacteristicsCharacteristics Some viruses cause disease Smallpox, measles, mononucleosis, influenza, colds, warts, AIDS, Ebola Some viruses may cause some cancers like leukemia Virus-free cells are rare MEASLES copyright cmassengale
- 16. 16 Viral ShapesViral Shapes 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 copyright cmassengale
- 17. 17 Helical VirusesHelical Viruses copyright cmassengale
- 18. 18 Polyhedral VirusesPolyhedral Viruses copyright cmassengale
- 19. 19 Complex VirusesComplex Viruses copyright cmassengale
- 21. 21 Viral TaxonomyViral 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 copyright cmassengale
- 22. 22 Viral TaxonomyViral Taxonomy ExamplesExamples Herpesviridae Herpesvirus Human herpes virus 1, HHV 2, HHV 3 Retroviridae Lentivirus Human Immunodeficiency Virus 1, HIV 2 copyright cmassengale
- 23. 23 Herpes VirusHerpes Virus SIMPLEX I and II copyright cmassengale
- 25. 25 Influenza VirusInfluenza Virus copyright cmassengale
- 26. 26 Chickenpox VirusChickenpox Virus copyright cmassengale
- 27. 27 Papillomavirus – Warts!Papillomavirus – Warts! copyright cmassengale
- 28. 28 RNA or DNA Virus Do or do NOT have an envelope Capsid shape HOST they infect Used for VirusUsed for Virus IdentificationIdentification copyright cmassengale
- 30. 30 PhagesPhages Viruses that attack bacteria are called bacteriophage or just phage T-phages are a specific class of bacteriophages with icosahedral heads, double-stranded DNA, and tails copyright cmassengale
- 31. 31 T-phagesT-phages The most commonly studied T-phages are T4 and T7 They infect E. coli , an intestinal bacteria Six small spikes at the base of a contractile tail are used to attach to the host cell Inject viral DNA into cell copyright cmassengale
- 32. Escherichia Coli Bacterium T - EVEN PHAGES ATTACK THIS BACTERIUM
- 34. 34 Diagram of T-4Diagram of T-4 BacteriophageBacteriophage Head with 20 triangular surfaces Capsid contains DNA Head & tail fibers made of protein copyright cmassengale
- 36. 36 Characteristics of RetrovirusesCharacteristics of Retroviruses Contain RNA, not DNA Family Retroviridae Contain enzyme called Reverse Transcriptase When a retrovirus infects a cell, it injects its RNA and reverse transcriptase enzyme into the cytoplasm of that cell copyright cmassengale
- 38. 38 RetrovirusesRetroviruses The enzyme reverse transcriptase (or RTase), which causes synthesis of a complementary DNA molecule (cDNA) using virus RNA as a template RTase copyright cmassengale
- 39. 39 RetrovirusesRetroviruses HIV, the AIDS virus, is a retrovirus Feline Leukemia Virus is also a retrovirus copyright cmassengale
- 40. 40 Viroids & PrionsViroids & Prions copyright cmassengale
- 41. 41 ViroidsViroids Small, circular RNA molecules without a protein coat Infect plants Potato famine in Ireland Resemble introns cut out of eukaryotic copyright cmassengale
- 42. 42 PrionsPrions Prions are “infectious proteins” They are normal body proteins that get converted into an alternate configuration by contact with other prion proteins They have no DNA or RNA The main protein involved in human and mammalian prion diseases is called “PrP” copyright cmassengale
- 43. 43 Prion DiseasesPrion Diseases Prions formPrions form insolubleinsoluble deposits in the braindeposits in the brain Causes neurons toCauses neurons to rapidly degeneration.rapidly degeneration. Mad cow diseaseMad cow disease (bovine spongiform(bovine spongiform encephalitis: BSE) is anencephalitis: BSE) is an exampleexample People in New GuineaPeople in New Guinea used to suffer fromused to suffer from kurukuru, which they got, which they got from eating the brainsfrom eating the brains of their enemiesof their enemies copyright cmassengale
- 44. 44 Viral ReplicationViral Replication copyright cmassengale
- 45. 45 Viral AttackViral Attack Viruses are very specific as to which species they attack HOST specific Humans rarely share viral diseases with other animals Eukaryotic viruses usually have protective envelopes made from the host cell membrane copyright cmassengale
- 46. 46 5 Steps of Lytic Cycle5 Steps of Lytic Cycle 1. Attachment to the cell 2. Penetration (injection) of viral DNA or RNA 3. Replication (Biosynthesis) of new viral proteins and nucleic acids 4. Assembly (Maturation) of the new viruses 5. Release of the new viruses into the environment (cell lyses) copyright cmassengale
- 47. 47 BacteriophageBacteriophage ReplicationReplication Bacteriophage inject their nucleic acid They lyse (break open) the bacterial cell when replication is finished copyright cmassengale
- 48. 48 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 Lytic Cycle ReviewLytic Cycle Review copyright cmassengale
- 49. 49 Attachment: Phage attaches to host cell. Penetration: Phage pnetrates host cell and injects its DNA. Merozoites released into bloodsteam from liver may infect new red blood cells 1 2 3 Bacterial cell wall Bacterial chromosome Capsid DNA Capsid Sheath Tail fiber Base plate Pin Cell wall Tail Plasma membrane Sheath contracted Tail core copyright cmassengale
- 50. 50 4 Maturation: Viral components are assembled into virions. Tail 5 Release: Host cell lyses and new virions are released. DNA Capsid Tail fibers copyright cmassengale
- 51. 51 One-step Growth CurveOne-step Growth Curve copyright cmassengale
- 52. 52 Viral LatencyViral Latency Some viruses have the ability to become dormant inside the cell Called latent viruses They may remain inactive for long periods of time (years) Later, they activate to produce new viruses in response to some external signal HIV and Herpes viruses are examples copyright cmassengale
- 53. 53 Lysogenic CycleLysogenic Cycle Phage DNA injected into host cell Viral DNA joins host DNA forming a prophage When an activation signal occurs, the phage DNA starts replicating copyright cmassengale
- 54. 54 Lysogenic CycleLysogenic Cycle Viral DNA (part of prophage) may stay inactive in host cell for long periods of time Replicated during each binary fission Over time, many cells form containing the prophages copyright cmassengale
- 55. 55 Viral LatencyViral Latency Once a prophage cell is activated, host cell enters the lytic cell New viruses form a & the cell lyses (bursts) Virus said to be virulent (deadly) INACTIVE STAGE ACTIVE STAGE copyright cmassengale
- 56. 56 Virulent VirusesVirulent Viruses HOST CELL LYSES & DIES copyright cmassengale
- 57. 57 The Lysogenic CycleThe Lysogenic Cycle copyright cmassengale
- 58. 58 Latency in EukaryotesLatency in Eukaryotes Some eukaryotic viruses remain dormant for many years in the nervous system tissues Chickenpox (caused by the virus Varicella zoster) is a childhood infection It can reappear later in life as shingles, a painful itching rash limited to small areas of the body SHINGLES copyright cmassengale
- 59. 59 Latency in EukaryotesLatency in Eukaryotes Herpes viruses also become latent in the nervous system A herpes infection lasts for a person’s lifetime Genital herpes (Herpes Simplex 2) Cold sores or fever blisters (Herpes Simplex1) SKIN TO SKIN CONTACT PASSED AT BIRTH TO BABY copyright cmassengale
- 61. 61 Lytic and Lysogenic CyclesLytic and Lysogenic Cycles copyright cmassengale
- 62. 62 Treatment for ViralTreatment for Viral DiseaseDisease copyright cmassengale
- 63. 63 VaccinesVaccines An attenuated virus is a weakened, less vigorous virus “Attenuate" refers to procedures that weaken an agent of disease (heating) A vaccine against a viral disease can be made from an attenuated, less virulent strain of the virus Attenuated virus is capable of stimulating an immune response and creating immunity, but not causing illness copyright cmassengale
- 64. 64 Other Viral TreatmentsOther Viral Treatments Interferon are naturally occurring proteins made by cells to fight viruses Genetic altering of viruses (attenuated viruses) Antiviral drugs (AZT) Protease inhibitors – prevent capsid formation copyright cmassengale