Lecture 3 Flashcards
What are the two functions of structural proteins?
Protecting the genome
Delivery of the genome
What is the capsid of a virus?
Protein shell surrounding the genome
What is a nucleocapsid?
Nuclei acid/protein complex within the virion
Term mostly used for enveloped viruses
What is the envelope of a virus
Host cell derived lipid bilayer
Derived from any host membrane, not only the plasma membrane
What is the virion?
Infectious viral particle
What are the two states of virus particles and what energy is involved?
Virus particles are metastable
- Stable: protect genome
- Unstable: must come apart upon infection
Energy is put into the virus particle during assembly
Potential energy used for disassembly if the cell provides the proper signal
How is metastability in viruses achieved?
Stable structure: symmetrical arrangement of many identical proteins -> provides maximal contact
Unstable structure: structure not usually permanently bonded together -> can be taken apart or loosened on infection to release or expose genome
What is electron microscopy?
Negative staining with electron dense material
Detailed structural interpretation impossible
What is Cryo-EM?
Freeze viral particles in water
Take a bunch of images
3D reconstruction of viruses
Can reach near-atomic resolution
What is X-ray crystallography?
Highest resolution but laborious
Not always possible to obtain crystals of capsids/virus particles
What did Watson and Crick discover in virology?
Identical protein subunits are distributed with helical symmetry for rod-shaped viruses
Platonic polyhedra symmetry for round viruses
What is a subunit?
Single folded capsid protein
What is a protomer?
Unit from which capsids or nucleocapsids are assembled, can be made of one or more subunits
What are capsomeres?
Are assembled from protomers
Ex of capsomere: pentamer and hexamer
What are VLPs?
Many capsid proteins can self assemble into virus-like particles
What are the two rules for “self-assembly”?
Rule 1: each subunit makes identical contacts with its neighbours
- Repeated interaction of chemical complementary surfaces at the subunit interfaces naturally leads to a symmetric arrangement
Rule 2: These bonding contacts are usually non-covalent and weak
- reversible/meta-stable bonds lead to error-free assembly
How many vertices, faces, and edges does an icosahedron have?
12 vertices
20 faces (equilateral triangle)
30 edges
20 three-fold axes of symmetry (one for each face)
12 five-fold axes of symmetry (one for each vertex)
30 two-fold axes of symmetry (one for each edge)
What is T?
of structural units in each triangular face of the icosahedron
Triangulation number, a measure of capsid size
Viruses with T>1 are made of hexamers and pentamers
How many pentamers and hexamers are there in an icosahedron and how many subunits?
12 pentamers
10(T-1) hexamers
60xT subunits
Describe the structure of a tailed bacteriophage
Head: icosahedral capsid
Contractile tail: attached to one fivefold access of the icosahedral capsid; built with helical symmetry
Baseplate for attachment
What are viral envelope glycoproteins?
Integral membrane glycoproteins
Ectodomain: attachment, antigenic sites, fusion
Internal domain: assembly
Oligomeric: spikes
How does the virus find the right cell to enter?
- Adhere to a cell surface (electrostatics) = no specificity
- Attach to specific receptors on cell surface
- Penetration
- Transport and uncoating (transfer genome inside the cell)
