Summary: Infectious Agents And Immunity

Read the summary and the most important questions on Infectious Agents and Immunity

• 1 Viruses

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• General structure of a virus

  Nucleic acid
  Nucleocapsid
  Sometimes an envelope with matrix and surface proteins

• According to which 4 characteristics are viruses classified?

  - DNA or RNA genome
  - Enveloped or naked
  - Dimension (size)
  - Symmetry of nucleocapsid

• What is the function of viral proteins? And name some examples

  Nucleocapsid protein, matrix protein, spike protein, enzymes
  The function of these viral proteins:
  - to protect the genome (nucleocapsid)
  - delivery of the genome to host cell (matrix)
  - enabling viral expression of genes (spike)

• What symmetry can the capsid have?

  - Helical
  - Icosahedron
  

  • equivalence
  • quasi equivalence

  - complex

• What is the function of matrix proteins?

  Link viral envelope with capsid, play a role in virus assembly

• What is the receptor for SARS corona, measles, HIV and influenza

  SARS corona - ACE II
  Measles - CD46
  HIV - CD4, CCR4, CCR5
  Influenza - sialic acid

• There are two ways of membrane fusion for a virus to enter the host

  1. PH independent fusion with the plasma membrane
  Virus attaches to host cell and this causes a conformational change that induces the virus and plasma membrane to fuse. The capsid is released in the cell.
  2. Acid activated fusion
  Virus is endocytosed and the endosome fuses with a lysosome. The acidic pH in the lysosome causes activation of the viral fusion domain and the virus membrane fuses with the membrane of the lysosome. The nucleocapsid is released.
  
  Can be tested through the addition of NH4Cl

• What is the general site where replication/transcription takes place for DNA and RNA viruses?

  DNA viruses in the nucleus, where they use host polymerases. The exception is poxvirus.
  RNA viruses usually replicate in the cytosol, they have to bring their own RdRp and use the ribosomes in the cytosol. Exception is the flu (influenza)
  
  RNA viruses in the cytoplasm cannot cut their mRNA (alternative splicing), because this normally takes place in the nucleus. They solve this by cutting the polyprotein (+RNA) or by subgenomic mRNA production (-RNA and +RNA).

• General characteristics of DNA virus replication

  - viruses push cell to S phase / keep them in S phase
  - host provides some enzymes (DNA and RNA polymerase)

• General characteristic of all RNA virus replication

  - Has to provide RdRp because host cell does not have this, they either encode this or bring it with hem