L5: Viruses

• viruses are an acellular microorganisms that cannot survive without a host: no metabolic abilities of their own - "a borrowed life"
• viruses rely completely on biosynthetic machinery of infected cell to multiply
• viruses infect all types of cells - obligate intracellular parasites
• viruses are the most abundant biological entities on the earth
• viruses consist of 2 parts: genetic material and capsid and in some cases a third part, envelope of lipids
• viruses genetic material is made from either DNA or RNA
• virus capsid is a protein coat that surrounds and protects the genetic material
• virus envelope of lipids that surrounds the protein coat when they are outside the cell
• capsids are made of multiple units of the same protein building block known as capsomers
• capsomers are a subunit of capsid arranged in a precise and highly repetitive pattern around the nucleic acid
• capsid/capsomers can be arranged in 3 types of symmetry: helical (TMV), icosahedral (adenovirus) and complex (bacteriophage)
• capsomers can also be called capsomeres
• what do viruses look like

  A) RNA

  B) capsomeres

  C) capsid

  D) protein spike

  E) DNA

  F) icosahedral

  G) helical

  H) 18 x 250 nm

  I) 70 - 90 nm

  J) 80-200 nm

  K) 80 x 225 nm

  
• a viral genome is made up of nucleic acid RNA and DNA. they could be linear (poxvirus), circular (hepatitis B) or segmented (influenza virus)
• viral genome sizes can vary from 4000 > 1 million nucleotides
• viruses infect all cell types like eukaryotic and prokaryotic and all forms of life. an organism a virus infects is called a "host organism". a cell a virus multiples is called a "host cell"
• some viruses infect bacteria like bacteriophages, virus that infect and replicate in bacteria
• bacteriophages were heralded as a potential treatment for diseases such as typhoid and cholera
• in 1940, the first electron micrograph of a bacteriophage was published. this silenced sceptics who had argued that bacteriophages were simple enzymes and not viruses
• lytic cycle of bacteriophage infection

  A) attach

  B) penetrate

  C) uncoat

  D) 20-30

  E) genome replication

  F) gene expression

  G) assembly

  H) release

  I) 100-200

  
• viruses infect us

  A) attach

  B) penetrate

  C) uncoat

  D) gene expression

  E) genome replication

  F) assembly

  G) release

  
• 1/2/3 can occur at the cell surface for some viruses
• SARS-CoV-2, the replication module has 16 proteins. It includes RNA polymerase to copy the genome. it has limited proof-reading so it makes some errors, generating variants, which allows tracking and leading to new strains
• the spike is critical for attachment and cell entry and a major target for neutralising immunity
• viruses must bind to a receptor protein to infect a cell
• sars-cov-2 replicaiton cycle

  A) spike binding to ACE2 receptor

  B) cell entry/fusion

  C) genome translation

  D) Viral RNA synthesis

  E) Viral mRNAs and genome

  F) translation

  G) assembly

  H) exocytosis