Chapter 19

• 20nm - not cell
• infect particel consisting of nucleic acid enclosed in a protein coat and or  some by membranous envelope
• Either DNA virus or RNA virus base on the kind of nucleric acid that makes up its genome

• protein shell enclosing the viral genome
• built from a large number of protein subunits capsomeres
• rodshaped olyhedral or more complex in shape
• Ex Tobacco mosaic = rigid rod shaped

• membranous envelopes surrounds the casids of influenza virus and other virus
• derived from membranes of host cell, contain host cells phosholipids and membrane proteins, glycoproteins
• Heres virus get membrane from nuclear envelope
• Animal virus has it but not much of bactoriophage

• virus that infect bacteris
• named T1 - T7
• T2,4,6 have similar structure - capsids have elongated icosahedral heads enclosing their DNA -> protein tail attach to head

• virus can infect cells of only a limited number of host species
• lock and key fit
• virus can infect specific species or tissue base on their host range.

Virus Enter cell with its DNA and Capsid - Host enzyme relicate the viral genome -> change into mRNA to make proteins -> genome and caside protein reassemble to make new virus - exit

• cycle that cuminates in death of the host cell
• last stage of infection
• virulent phage:
• Attachment -> inject DNA -> Synthesis of viral genomes and proteins -> assembly -> release

restricts the ability of the phage to infect  the baterium once it identify the DNA as foreign

• allows replication of the the phage genome without destrying the host
• temperate phages - capable of using both modes of replicating within a bacterium                
• Prohage - Phage DNA integrates into bacterial chromosome (different from lytic cycle) -> it may affect cells phenotype

• RNA animal virus with the most complicated  replication cycles
• has reverse transciptase - enzyme transcribes an RNA template to DNA. RNA -> DNA flow, the opposite of the usual direction.
• Causes HIV and AIDS

Reverse transcrtase molecule released into cytoplasm - > new viral DNA -> provirus - intergrated viral DNA that never leaves the host cell.

• Mutation
• Dissemination
• Spread of virus from animal
• Influenza A- infect both animals and human

• 16 differnt types
• helps flu virus to attach to host cells

• 9 types
• enzymes that help release virus particles fom the cell

• Horizontal - plant infect by an external virus
• Vertical- inheirit virsu from it parent plants

simple virus made of RNA molecules, inect plants

• infectious proteins
• causes degenerative brain disease in animal
• EX;mad cow, Creutzelub Jacob
• indestructible, 10 years incubation period
• convert other cell proteins to prion protein