LU3 Molecular Virology Past Paper PDF

LU3: Molecular Virology- General Classification, Morphology and Replication  Kingdoms of Life Eukaryotic Plants Fungi Animal Multicellular Protista Eukaryotic Protozoa Alga Unicellular Monera/Prok...

LU3: Molecular Virology- General Classification, Morphology and Replication  Kingdoms of Life Eukaryotic Plants Fungi Animal Multicellular Protista Eukaryotic Protozoa Alga Unicellular Monera/Prokaryotae Prokaryotic Eubacteria Archaea Unicellular No Cellular Virus Viroid Prion Structure  History of Viruses 3000 BC – Egyptian with symptom of polio 1798 - Edward Jenner vaccination (small pox) 1892 - Iwanoska – TMV 1898 - Beijerinck living infectious fluid 1935 - Stanley crystallized virus: protein 1952 - Hershey & Chase: DNA infectious 1960’ s - Cell culture to propagate viruses Polio infection Edward Jenner Viral characteristics  DNA or RNA genome (but not both)  Genome: 1 or 2 strands (DNA or RNA)  No energy generating system  Obligate intracellular parasite  Small size – range 30 -300nm  Many shapes (eg., cylindrical, icosahedral)  Does not undergo binary fission  Variety of hosts  Hosts of Viruses Specificity  Only one species  Limited hosts  Hosts within the same species  Different species  Infecting different organisms Varieties of Hosts  Animals  Plants  Fungi  Bacteria  Size and Shape of Virus Sizes: 20 nm – 330 nm Poliovirus 30 nm; poxvirus 330x220x100 nm Size: Nucleocapsid; virion Shapes of Virus Spherical (icosahedron) - poliovirus Elongated – TMV (330 x 17 nm) Complex - bacteriophage T4 Size + shapes = morphology  Human cell 1000 nm Nucleus 2,800 nm 1000 nm x 2000-3000 nm Smallpox 230 nm Adenovirus, 70 nm Perbandingan saiz virus Escherichia coli Human liver cell Size and Shapes Spherical/icosahedron examples poliovirus adenovirus Elongated/rod, example TMV  Components of Virions Nucleic Acid Genome – DNA or RNA Genome molecules – 1 or 2 stranded Capsid – protein coat Protein subunit protein = capsomere Different size and types Nucleic acid & capsid = Nucleocapsid Lipoprotein envelope (some viruses) Glycoprotein spikes (host) Virion=infectious virus particles Poliovirus Naked Helical Naked Helical  Are coded by Viral Genes (and made only while a virus is infecting a cell); They… 1. Protect the viral nucleic acid Virus Proteins… 2. Attach to receptors on the outside of cells 3. Penetrate cell membranes 4. Replicate viral nucleic acid (proteins with this function are not associated with all virus types) 5. Begin the program for virus replication (ditto) 6. Modify the infected cell (beyond towards making new virus particles; ditto) Enveloped “Spherical” (HIV)  Poxvirus Rabies virus Herpesvirus  Viruses are classified: 1. According to their Genome Type Virus Classification 2. Their Virion Morphology (as determined by electron microscopy, presence of envelope) 3. Their strategies of replication 4. Their Serology (serotype), which is their reaction with specific antiserum 5. (Increasingly) in terms of the sequence of their genomes International Committee on Taxonomy of Viruses (ICTV) Viral Taxonomy Family genus virus type strain serotypes Classification of virus based on viral component  Classification of virus based on viral component Virus RNA DNA Single Single Double Double strande strande strande stranded d d d No Envelop No Envelop No Envelop No Enveloped envelope ed envelope ed envelope ed envelope Bunyaviru Polio Retrovir Adenovi Parvovi Cystovi ?? Reovirus s virus us rus rus ridae Poliovirus – Picornaviridae; Viroid = virus without coat protein Influenza Virus - Orthomyxoviridae Prion = protein molecule which can replicate  RNA Virus Families Picornaviridae Reoviridae Togaviridae Coronaviridae Orthomyxoviridae Rhabdoviridae Paramyxoviridae Arenaviridae Retroviridae Flaviviridae DNA VIRUSES Herpesviridae Adenoviridae Papovaviriade Poxviridae Parvoviridae Hepadnaviridae  Virus Replication Cycle Stage 1 - Attachment Stage 2 - Entry/uncoating Stage 3 - Synthesis o Proteins o Genome replication Stage 4 - Assembly Stage 5 - Maturation and Release  Different Types of Genome Replications Class I - dsDNA (herpesvirus) Class II - ssDNA (parvovirus, fX174) Class III - dsRNA (Reovirus) Class IV - ss(+)RNA (poliovirus) Class V - ss(-)RNA (Influenza virus) Class VI - ss(+ retro)RNA (HIV)  DNA-2b RNA-2b DNA-1b + + - mRNA New particles + - + - - - - Class I Class II Class III New particles New particles mRNA RNA-1b +ve Reverse RNA-1b RNA-1b -ve mRNA Class VI Class IV Class V - + dscDNA RF -+ + - RNA-cDNA RI mRNA hybrid New particles New particles New particles Assembly Put together viral components Formation of nucleoprotein Specific structures No energy required – self assembly Sites differ: – DNA virus– nucleus (except Poxvirus) – RNA Virus - Cytoplasm Lambda Lytic vs.Lysogenic Cycles Lambda Lytic vs.Lysogenic Cycles Phage  is a Temperate phage Which means that it capable of displaying Lysogeny One consequence of lysogeny is lysogenic conversion (a.k.a., phage conversion) which is a change in bacterial phenotype upon lysogenization A number of bacterial virulence factors, including toxins, are coded by temperate Prophages including the Shigatoxin produced by lambdoid phage of O157:H7 HIV = Retrovirus  Cytopathic effects (CPE) are harm viruses Cytopathic Effects can do to cells, short of totally destroying cells