Micro Lec 3 Flashcards
Viral classification
Artificial system not based on evolutionary relationships. Most important characteristics in viral taxonomy are type of nucleic acid, nucleic acid strandedness, nucleic acid configuration, presence of envelope, whole virion morphology, and host range.
Families of Bacterial Viruses
all bacterial viruses are referred to as bacteriophages or phages. Nonenveloped and 8 of the 10 families contain d.s. DNA.
Families of Plant Viruses
Most are nonenveloped and contain s.s RNA
Families of vertebrate Viruses
total of 25 families. 15 only infect vertebrates and 10 also infect invertebrates. Single largest family group consists of enveloped s.s RNA viruses
Bacterial Viruses
most studied bacteriophages are those that infect E. col. Two most common examples are T even phage and bacteriophage
T even phages (lytic cycle)
Virulent phage. 1) Attachment- tail fibers attach to receptors on E. coli. 2) Penetration- phage tail releases phage lysozyme which breaks down the murein layer and move towards the PM and the phage DNA is injected into the cell. 3) Replication- host cells protein synthesis stops and copies of phage DNA are made, then viral proteins are made. 4) Maturation- Assembly of complete virions come together. 5) Release- Lysis of cells leads to release of new phage. Cell wall breaks down because lysozyme encoded by phage gene is synthesized with the mall.
Bacteriophage
Lysogenic cycle of bacteriophage. 1) Attachment. 2) Penetration. 3) Integration of phage DNA- phage DNA becomes a part of bacterial chromosomes, inserted DNA is called prophage. 4) Latency- Phage DNA remains in chromosome as cell replicates its DNA and divides. Prophage can leave chromosome and enter lytic cycle.
Animal Virus stage of infection Nonenveloped viruses
1) Attachment - specific protein on capsid bind to specific receptors on host cell. 2) Penetration- capsid enters through phagocytosis (engulfs a solid particle to form an internal compartment known as a phagosome). 3) Replication- 1st uncoating, 2nd host cells protein synthesis steps, 3rd viral nucleic acid is copied, 4th capsid or other proteins are synthesized (DNA viruses are copied in nucleus, RNA in cytoplasm) 4) Maturation- assembly of capsid plus packaging of nucleic acid into capsid. 5) Release- PM of host cell is lysed to release viruses.
Animal Virus stage of infection Enveloped viruses
1) Attachment- Envelop proteins can serve as attachment sites for specific receptors on host cell. 2) Penetration- capsid enters cell via membrane fusion 3) Replication- 1st uncoating, 2nd host cells protein synthesis steps, 3rd viral nucleic acid is copied, 4th capsid or other proteins are synthesized (DNA viruses are copied in nucleus, RNA in cytoplasm) 4) Maturation- assembly of capsid plus packaging of nucleic acid into capsid. 5) Release- As capsid approaches PM, membrane surrounds it and pinches it off budding envelope comes from host cell and host cell is not lysed.
