Transcript Chapter 13a
TORTORA • FUNKE • CASE Microbiology AN INTRODUCTION EIGHTH EDITION B.E Pruitt & Jane J. Stein Chapter 13, part A Viruses, Viroids, and Prions Viruses • Are very small • Viruses contain DNA or RNA • And a protein coat • Capsid with Capsomeres • Some are enclosed by an envelope • Acellular • Obligate intracellular parasites • No ATP generating system • No Ribosomes or means of Protein Synthesis • Some viruses have spikes • Most viruses infect only specific types of cells in one host Viruses: only 1 nucleic acid • Nucleic Acid • DNA or RNA (But never both) • ssDNA • ds DNA • ss RNA • ds RNA Viruses are small Figure 13.1 Shapes of Viruses: Helical Figure 13.4a, b Shapes: Polyhedral icosahedral Figure 13.2a, b Shapes: Complex Viruses Figure 13.5a Envelope • Membrane may be around capsid • It may contain spikes Viral Taxonomy • 1. Nucleic Acid • 2. Morphology • 3. Strategy for replication • 4. Symptoms • 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 e.g. HHVII Growing Viruses • Viruses must be grown in living cells. • The are never grown in culture media • Bacteriophages form plaques on a lawn of bacteria. Plaques on E. coli Ø Growing Viruses • Animal viruses may be grown in living animals or in embryonated eggs. • Vaccine virus in eggs Figure 13.7 Viral cultures • 1. Primary Cell Lines • die out after a few generations • 2. Diploid Cell Lines • derived from human embryos • maintained for up to 100 generations • 3. Continuous Cell Lines • Transformed Cells (Cancerous Cells) • may be maintained indefinitely • HeLa Cells • Henrietta Lacks 1951 (Cervical Cancer) Growing Viruses • Animal and plants viruses may be grown in cell culture. • Continuous cell lines may be maintained indefinitely. Figure 13.8 Virus Identification • Cytopathic effects CPE Negri bodies rabies • 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 Virus Identification Cytopathic effects CPE Figure 13.9 Multiplication of Bacteriophages (Lytic Cycle) APBMR - Bacteriophage Lytic multiplication 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 Bacterial cell wall Bacterial chromosome Capsid DNA Capsid Sheath Tail fiber 1 Attachment: Phage attaches to host cell. Base plate Pin Cell wall Tail Plasma membrane 2 Penetration: Phage penetrates host cell and injects its DNA. Sheath contracted Tail core 3 Biosynthesis: DNA is copied and capsomeres are produced Figure 13.10.1 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 One-step Growth Curve Burst size and Burst time during Eclipse Period Eclipse period no whole virions Figure 13.11 Lytic cycle versus Lysogenic • Lytic cycle Phage causes lysis and death of host cell • Lysogenic cycle Prophage DNA incorporated in host DNA The Lysogenic Cycle Figure 13.12 Specialized Transduction Prophage gal gene Bacterial DNA 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. gal gene 3 Phage matures and cell lyses, releasing phage carrying 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 Multiplication of Animal viruses Same as bacteriophage except must uncoat • 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