Viruses and other non cellular parasites • Viruses: • Classification • Viruses and diseases • Other non-cellular infection particles • Practical part: • Titration of bacteriophage by plague number • Titration of bacteriophage in a broth culture • Teachers: • Vítek Kříž (e-mail: firstname.lastname@example.org) • Monika Kubíčková (e-mail:email@example.com)
Viruses are acellular organisms whose genomes consist of nucleic acid, and which obligately replicate inside host cells using host metabolic machinery and ribosomes to form a pool of components which assemble into particles called virions, which serve to protect the genome and to transfer it to other cells. • The concept of a virus as an organism challenges the way we define life: • * viruses do not respire, • * nor do they display irritability; • * they do not move • * and nor do they grow • Viruses are quite respectable as organisms: • * they most definitely replicate, • * their evolution can (within limits) be traced quite effectively, and • * they are independent in terms of not being limited to a single organism as host.
Viral structure A complete virus particle (virion) consisting nucleic acid surrounded by a protective coat of protein (capsid). A capsid is composed of proteins encoded by the viral genome and its shape serves as the basis for morphological distinction. Proteins associated with nucleic acid are known as nucleoproteins, and the association of viral capsid proteins with viral nucleic acid is called a nucleocapsid. Protein capsid of many viruses are able to envelope themselves in a modified form of one of the cell membranes - the outer membrane surrounding an infected host cell, or from internal membranes such as nuclear membrane or endoplasmic reticulum - thus gaining an outer lipid bilayer (viral envelope).
Eukaryotic cell infected by virus Prokaryotic cell infected by bacteriphage/phage Classification according to the host
Classification according to genome: • DNA viruses (ds DNA: λ phage, Human herpseviruses , Variola virus, ssDNA:Parvovirus B19) • RNA viruses (dsRNA Rotavirus, +ssRNA: Rubellav., Hepatitis v., Yellow fever, -ssRNA: Influenza v., Rabies v., Measles v.) • Viruses dependent on RT (-ssRNA-RT: HIV-1, dsDNA-RT: Hepatitis B)
Central dogma: Reverse transcription RNA>>>>>>DNA Reverse transcriptase
Classification according to the cycle • Lytic-cell • Lysogenic-integration into cellular genome Copy from http://encarta.msn.com/media_461516656_761575740_-1_1/Lytic_and_Lysogenic_Cycles_of_a_Bacteriophage.html Movie lytic/lysogenic cycle http://highered.mcgraw-hill.com/sites/0072556781/student_view0/chapter17/animation_quiz_2.html
Viruses and diseases • Antibiotics do not work • Vaccination antiviral drugs
Herpes simplex virus 1 • Genome: dsDNA • Transmision: by direct contact with the skin or from saliva • Disease:Cold sore (Herpes), (encephalitis) • Treatment: Acyclovir (nucleoside analogues)
Influenza virus (Orthomyxoviridae) • Genome: ssRNA • Disease: fever, sore throat, muscle pains, gastroenteritis, pneumonia (can be fatal). • Treatement: vaccine, neuraminidase inhibitors (particularly effective). • Influenzavirus A (birds, mammals). The most virulent. Labeled according to an „H“ (hemagglutinin) and an „N“ (neuraminidase). Both are large glycoproteins found on the outside of the viral particles. (e.g. H1N1 - Spanish Flu). • Influenzavirus B (humans, seals), common human epidemics. • Influenzavirus C (humans, pigs), local epidemics (less virulent).
HIV-1 • Genome: Two strains of ssRNA • Transmision: by sexual intercourse or by blood • Disease: Acquired immune deficiency syndrome (AIDS) • Treatment: nucleoside anologues, reverse transcriptase inhibitors colour-enhanced electron microscope image, 24,000´ magnification
Viroids • Plant pathogens that consist of a very short circular, single-stranded RNA without the protein coat that is typical for viruses. • Viroid RNA does not code for any known protein. • Viroids are usually transmitted by seed or pollen. Infected plants can show distorted growth.
Prions • Infection agent: protein (PrPSc) catalyse normal PrPC proteins into the infectious isoform (conformation chage) • none nucleotide acid is detected • Transmision: Process is not clear, probably through ingestion • Disease: Creutzfeldt-Jakob disease (human), kuru (human), BSE (cattle), Scrapie (sheep) • Treatment: resistant to denaturation (134 degrees Celsius for 18 minutes ) Copy from> http://www.stanford.edu/group/virus/prion/2004anderson/index.html http://www.osel.cz/index.php?clanek=699