Chapter 13 Lecture Outline - Viruses, Viroids, and Prions PDF

Chapter 13 Viruses, Viroids, and Prions 1 General Characteristics of Viruses What is the size range of viruses? Figure 13.1 2 General Characteristics of Viruses How is viral structure unique?  Acellular  Single type of nucleic acid present - DNA or RNA What are the structural components of a typic...

Chapter 13 Viruses, Viroids, and Prions 1 General Characteristics of Viruses What is the size range of viruses? Figure 13.1 2 General Characteristics of Viruses How is viral structure unique?  Acellular  Single type of nucleic acid present - DNA or RNA What are the structural components of a typical virus?     Core Capsid Envelope Spikes Where do viruses multiply?  Inside living host cells  “Obligate Intracellular Parasites” 3 General Characteristics of Viruses What is the host range of viruses? Virus Host Cell Plant Virus Plant Cell Animal Virus Animal Cell Bacterial Virus (Bacteriophage) Bacterium What is the tissue range of viruses? Viral Disease Tissue Viral Hepatitis Viral Encephalitis Liver Brain How are viruses transmitted? 4 Virus Terminology - What is a “phage?” “Phage” - represents the word “virus” What is a bacteriophage? What is the host cell for a bacteriophage? What is phage DNA? Whose DNA does it belong to? 5 General Morphology of Viruses Capsid Architecture Helical viruses Polyhedral viruses Complex viruses Figure 13.4 Figure 13.5 a Figure 13.2 6 Viral Taxonomy Family names end in -viridae  Herpesviridae, Retroviridae Genus names end in -virus  Enterovirus, Influenzavirus Viral species - a group of viruses sharing the same genetic information and ecological niche (host)  HIV, SIV Viral subspecies/strains  HSV-1, HSV-2 7 Growing Viruses in The Laboratory Bacteriophages Are grown in bacteria Form plaques  Corresponds to a single virus  Can be expressed as plaqueforming units (PFU) Can bacteriophage grow in animal cells? Figure 13.6 8 Growing Viruses in The Laboratory Animal Viruses Grown in living animals, embryonated eggs or animal tissue cultures Virally infected animal cell detected via its deterioration, which is called cytopathic effect (CPE) Can animal viruses grow in bacterial cells? Figure 13.7 9 Viral Identification and Multiplication Virus Identification  Cytopathic effects (CPE)  Serological tests - the most common method  Polymerase Chain Reaction (PCR) Virus Multiplication........(vs. Reproduction)  Virus must invade a living host cell  Virus must take over host’s metabolic machinery (host’s DNA) 10 Multiplication of Bacteriophages Bacteriophages can multiply by: 1. Lytic Cycle Phage causes lysis and death of the bacterial host cell 2. Lysogenic Cycle Phage does NOT cause death of host cell Phage DNA is incorporated into the bacterial host cell’s DNA Virion = newly-formed, mature virus 11 12 The Bacteriophage Lytic Cycle What are the stages of the Lytic Cycle for Bacteriophages? 1. Attachment 2. Penetration 3. Biosynthesis 4. Maturation 5. Release What are the key events in each stage of the Lytic Cycle? 13 The Bacteriophage Lytic Cycle Figure 13.11 14 The Bacteriophage Lytic Cycle 1. Attachment Bacterial virus uses its tail fibers to attach to cell wall receptors of bacterial host cell Viral lysozyme (enzyme) makes hole in bacterial cell wall (so that viral DNA can enter host cell; the entire bacterial virus does not enter) 2. Penetration Viral sheath is contracted which will push the viral DNA into bacterial host cell Viral DNA now present in bacterial host cell 15 The Bacteriophage Lytic Cycle 3. Biosynthesis Viral DNA incorporates into bacterial host DNA and takes over bacterial host cell’s DNA Bacterial host forced/committed to make viral components through transcription & translation 4. Maturation Viral components get assembled into virions Virions are newly-made, mature viruses capable of infecting other cells 16 The Bacteriophage Lytic Cycle 5. Release Bacterial host cell lyses or ruptures when new virions are released Results in death of bacterial host cell 17 The Bacteriophage Lysogenic Cycle Lysogeny - phage DNA integrates & remains “dormant” in a host cell; phage particle (protein) production is delayed How does Lysogeny happen? Phage DNA gets incorporated into host cell DNA  forms a prophage When the host cell replicates, it also replicates the prophage and does NOT lead to production of phage particles in host cell Lysogeny alters host cell’s characteristics and results in: 1. Phage conversion: non-pathogenic bacteria  pathogenic bacteria 2. Latent viral infections: virus “hides out” 3. Transformation: virus induces cancer-causing genes to get expressed 18 19 The Bacteriophage Lysogenic Cycle Figure 13.12 20 Multiplication of Animal Viruses What are the stages of multiplication (Lytic Cycle) for Animal Viruses? 1. 2. 3. 4. 5. 6. Attachment Entry - by receptor-mediated endocytosis (RME) or fusion Uncoating - by viral or host enzymes to expose the genetic core Biosynthesis Maturation Release - by budding or rupture 21 Entry of Animal Virus into Animal Host Cell Animal viruses: Enveloped virus vs Non-enveloped virus Two ways virus enters animal host cell: 1.Enveloped viruses enter by Fusion 2.Non-enveloped viruses enter by Receptor-Mediated Endocytosis 22 Uncoating of Animal Virus Capsid After entry of capsid into animal host cell, protein capsid must be disintegrated to expose the viral DNA Recall:  All viral parts come from different proteins made through translation 23 24 DNA vs RNA Animal Viruses DNA of Animal Viruses Animal virus DNA incorporates into animal host cell’s DNA  forms a provirus RNA of Animal Virus Animal virus RNA cannot incorporate into animal host cell’s DNA Animal virus RNA must get converted to DNA by enzyme Reverse Transcriptase  Animal virus DNA can now incorporate into animal host cell’s DNA to form a provirus  Ex - Retroviridae Family (HIV) 25 26 Release of Animal Virus from Animal Host Cell Two ways animal virus is released from animal host cell: 1. Enveloped animal viruses are released by Budding 2. Non-enveloped animal viruses are released by Rupture Figure 13.20 27 28 DNA vs RNA Animal Virus Families DNA Viruses Adenoviridae Respiratory infections Papovaviridae Warts, cervical & anal cancers RNA Viruses Retroviridae 😃 HIV/AIDS COVID-19 Poxviridae 😃 Smallpox & Cowpox Herpesviridae 😃 Cold sores, Chickenpox, Shingles Hepadnaviridae Hepatitis B & liver cancer 29 Viruses and Cancer Some cancers are caused by viruses called oncoviruses May develop long after viral infection Some oncoviruses can “turn on” oncogenes found in normal cells  uncontrolled cell division  transform normal cells into cancerous cells; How does this happen?  Oncovirus’ DNA becomes integrated into the host cell’s DNA and induces tumors (turns on oncogenes) 30 Infectious Viruses 1. Acute Viral Infections Rapid onset of symptoms & short duration infection Ex - Influenza 2. Latent Viral Infections Hidden, inactive, dormant infection Ex - Genital Herpes, Shingles 3. Persistent/Chronic Viral Infections Late onset of symptoms, long duration, subclinical symptoms Ex - HIV/AIDS 31 Viroids and Prions Viroids Smallest infectious pathogens in the world! Infectious RNA molecules Causes plant diseases (Ex - Potato Disease) Prions Infectious protein particles Highly resistant! Cause transmissible neurological disease  Spongiform Encephalitis: 1. Mad Cow Disease (Bovine Spongiform Encephalopathy) 2. Creutzfeldt-Jakob Disease (CJD) 3. Sheep Scrapie 32