Lecture 3: Virus Structural Diversity Flashcards
A virus is normally much __ than the host cells in which it replicates.
smaller
How big is the Acathhameba?
15 to 25 uM
How big is the world’s largest virus?
1.5 x 0.5 um. It is large enough to see with a light microscope.
How big is E coli?
1 x 2 uM
How big is the smallest animal virus polio?
24 x 24 nm
How big is the largest animal virus (pox)?
0.3 x 0.3 uM
Bacterial cells vary in size by ___ orders of magnitude the smallest being just ___ in diameter
a) 4 b) 0.15 uM
The largest bacterial ___ are smaller than the smallest bacterial ___
a) viruses b) cell
How were viruses first discovered?
First discovered as infectious agents that passed through filters which retained the smallest cells (bacteria) the pores of these filters were 0.3 uM in diameter.
Are all viruses 0.3 uM (300 nm) in diameter?
No, there are some viruses in amoeba that cannot pass through a filter and are named giant viruses.
Describe giant viruses
They behave in the same way as all other viruses they just are larger. Two examples are megavirus and pithovirus. (Giant viruses that replicate in animal cells or cause disease have not been discovered yet).
Describe sub viral agents
At the lowest end of the size scale there are infectious entities that are smaller than a virus.
Ex. satellite/ crippled virus that can only replicate in the presence of a real virus (helper virus).
Describe a satellite virus
Helper virus is required
Its genome is protein-encapsidated
Its genome encodes its capsid protein
Describe a satellite nucleic acid
Helper virus is required
Its genome is protein encapsidated
Its genome does NOT encode its capsid protein
Describe a viroid
No helper virus is required.
Genome is not protein encapsidated
Genome does not encode capsid protein
Viroid is just a piece of RNA
Simplest known infectious agent.
May have descended from a virus or vice versa
What makes up the exterior of a viral structure?
Exterior: proteins for protecting the genome and attaching to the cell surface at the start of infection.
What makes up the interior of a viral structure?
Interior: nucleic acid genome usually engaged with nucleic acid-binding proteins.
What is the naked capsid virus?
exterior= protein shell: rugged release of new virons from cell requires cell lysis.
What is the capsid?
name of exterior protein shell
What is the core?
Interior nucleic acid (genome) maybe complexed with proteins. Core proteins if they exist are sometimes known as non-structural proteins (may be histone-like or include enzymes for genome expression/replication).
What is an enveloped virus?
outer layer = lipid envelope
less rugged cell lysis generally not required for viron exit
What is an envelope?
flexible lipid bilayer containing virus encoded transmembrane proteins (envelope is picked up from cell plasma membrane during virus exit).
What is an matrix protein?
lines inside of the envelope = protein sac either rigid or flexible that supports envelope holds genome /NP
What is an nucleocapsid?
Interior protein/nuclic acid (genome) complex like human chromatin. The major genome binding protein may be referred to as nucleoprotein.
