Lecture 16. Viral Structure Flashcards
What is the structure of viruses?
Nucleic acid (DNA or RNA)
Protein coat (capsid)
Viral envelope (Derived from host cell)
Viral attachment proteins
What is the cellular receptor of SARS-CoV-2?
ACE2
What is a capsid?
The protein shell that surrounds viral genome
Composed of a number of protein molecules arranged in a precise and highly repetitive pattern around the nucleic acid
What is the viral envelope?
Envelope is bilayer phospholipid membrane derived mainly from the host cell
What is a virion?
The complete virus particle
What information is encoded in the viral genome?
Nucleic acid (DNA or RNA)
Structural proteins (capsid proteins, VAPs…)
Non-structural proteins
What is not encoded in viral genomes?
No genes encoding the complete protein synthesis
machinery(eIFs, tRNAs..)
No genes encoding proteins involved in cell wall production or membrane biosynthesis
No centromeres or telomers found in standard host chromosomes
What is the capsomere?
Subunit of the capsid
Smallest morphological unit visible with an electron microscope
What shape are most viral particles?
Either rod or round
How are round viruses arranged?
Identical protein subunits are arranged in icosahedral symmetry
How are rod viruses arranged?
Rod viruses are arranged in helical symmetry
How is metastability achieved?
Stable structure achieved by symmetrical arrangement of many identical viral protein subunits provide maximal
contact
Each subunit has identical bonding contacts with its neighbours and this repeated interaction at the subunit interfaces natural provides symmetric arrangement
What makes a virus structure unstable?
The contact is not covalent (not usually permanently bounded together)
Can be dissociated or taken apart once the virus attaches to the host cell to release the genome
What can some viruses self-assemble into?
Virus-like particles (VLPs)
What symmetry can capsids have?
Helical
Icosahedral
Complex
What is a subunit?
Single folded polypeptide chain
What is a structural subunit?
Unit from which the capsid is built-one or more subunit
What is an icosahedron?
20 faces – each an equilateral triangle
30 edges – each an interface between 2 faces
12 vertices – each a point where 5 faces meet
What are icosahedral capsids made of?
60 identical protein subunits
How are bigger icosahedral viruses built?
By adding more subunits
Pentons and hexons
What viruses have icosahedral symmetry?
Poliovirus
Rotavirus
Varicella-zoster virus
Reovirus
What does the herpes simplex virus capsid contain?
Holes for entry and exit of DNA
What is an example of a virus that has helical symmetry?
Tobacco Mosaic Virus (TMV)
What determines the length of viruses with helical symmetry?
Length of nucleic acid
What determines the width of viruses with helical symmetry?
Size and packaging of protein subunits
What are examples of viruses that have complex symmetry?
Poxviruses and some bacteriophages
What does the presence of a viral envelope confer?
Instability on the virus
