Virology

   Isaac Asimov: Life and Energy   

Helical Symmetry

Coat protein molecules engage in identical, equivalent interactions with one another and with the viral genome to allow construction of a large, stable structure from a single protein subunit.

metastable

Tags:virology, helical, symmetry, virus, structure

Source:https://youtu.be/3olXpSqEOmY

   Isaac Asimov: Life and Energy   

+ vs - Strand RNA Viruses

The positive strand RNA viruses are ready to be translated when they enter the cell. The negative strand RNA viruses have to first be copied by the RNA polymerase that's in the virus particle.

Tags:virology, RNA

Source:https://youtu.be/3olXpSqEOmY

   Isaac Asimov: Life and Energy   

Helical Viruses Envelope

Turns out that all known animal helical structure viruses have a nucleocapsid with an envelope around it. Plant helical viruses don't have the envelope. They are made of capsids enclosing the RNA.

Tags:virology, envelope, helical

Source:https://youtu.be/3olXpSqEOmY

   Isaac Asimov: Life and Energy   

Round Capsids

All round capsids have precise number of proteins; multiples of 60 are common (60, 180, 240, 960).

Tags:virology, capsid, structure, unit

Source:https://youtu.be/3olXpSqEOmY

   Isaac Asimov: Life and Energy   

Caspar & Klug

Caspar and Klug discovered in 1962 that round capsids are icosahedrons. Capsid subunits tended to be arranged as hexamers or pentamers.

Tags:virology, capsid, structure, unit, pentamer, hexamer, icosahedron

Source:https://youtu.be/3olXpSqEOmY

   Isaac Asimov: Life and Energy   

Icosahedral symmetry

Icosahedron is a platonic solid with 20 faces, each an equilateral triangle. It has 5x, 3x, and 2x axes of symmetry (12 each). Allows a formation of a small shell with smallest number (60) of identical subunits.

icosahedral symmetry

Tags:virology, envelope, helical

Source:https://youtu.be/3olXpSqEOmY

   Isaac Asimov: Life and Energy   

Simple Icosahedral Capsid

Made of 60 identical subunits represented as commas in the image. Each subnit is an identical type of protein. Interactions of all molecules with their neighbors is identical (head to head, tail to tail). The particles are spherical, not icosahedral.

icosahedral symmetry

Tags:virology, capsid, structure, unit, pentamer, hexamer, icosahedron

Source:https://youtu.be/3olXpSqEOmY

   Isaac Asimov: Life and Energy   

Larger Icosahedral Capsid

Uses 3 different proteins. Made of pentamers and hexamers (unlike simple icosahedral capsids, which are made of pentamers only). Three modes of subunit packing (orange, yellow, purple). Quasiequivalent bonding interactions: all engage in head to head and tail to tail interactions. 180 identical protein subunits in the example below.

icosahedral symmetry

Tags:virology, capsid, structure, unit, pentamer, hexamer, icosahedron

Source:https://youtu.be/3olXpSqEOmY

   Isaac Asimov: Life and Energy   

T Number

The number of smallest triangular structures making up the triangular face of an icosahedron.

t number

Tags:virology, capsid, structure, unit, t-number, icosahedron

Source:https://youtu.be/3olXpSqEOmY

   Isaac Asimov: Life and Energy   

T Number Examples

The following are T number structure example:

t number

Tags:virology, capsid, structure, unit, t-number, icosahedron

Source:https://youtu.be/3olXpSqEOmY

   Isaac Asimov: Life and Energy   

Large Complex Capsids

Below is an example of a large complex capsid with T=25.

complex capsid

Tags:virology, capsid, structure, unit, t-number

Source:https://youtu.be/3olXpSqEOmY

   Isaac Asimov: Life and Energy   

Rioviruses

Rioviruses have two shells - inner and outer.

two shell virus

Tags:virology, capsid, structure, riovarus

Source:https://youtu.be/3olXpSqEOmY

   Isaac Asimov: Life and Energy   

Tailed Bacteriophages

Tailed bacteriophages use a combination of a capsid attached to a helical tail attached to a baseplate. The genetic material is in the capsid stored under a high pressure. Upon attachment to the cell, the baseplate penetrates the cell membrane and the genome is injected into the cell.

tailed bacteriophages

Tags:virology, capsid, structure, tailedbacteriophage, bacteriophage, baseplate, tail

Source:https://youtu.be/3olXpSqEOmY

   Isaac Asimov: Life and Energy   

Bacteriophage Spike

The image below shows a bacteriophage's spike that protrudes from the viruses' tail and penetrates the cell membrane before injecting the genetic material. The spike is made of 3 copies of a single protein. The tip of the spike proteins are held together by a single iron ion.

bacteriophage spike

Tags:virology, capsid, structure, bacteriophage, spike

Source:https://youtu.be/3olXpSqEOmY

   Isaac Asimov: Life and Energy   

Herpes Simplex Virus Capsid

The herpes viruses contain a nucleocapsid with an envelope. The capsid has holes in one of the proteins that acts as a portal for the DNA to get into the shell during assembly and out of the shell for infection.

herpes capsid

Tags:virology, capsid, structure, herpes, portal, DNA

Source:https://youtu.be/3olXpSqEOmY

   Isaac Asimov: Life and Energy   

Membrane Budding

Both helical and icosahedral viruses have membranes around them. The membrane is a lipid bilayer that comes from the host. The process of acquiring the memberane is called budding. The nucleocapsid forms under the membrane and then the whole structure buds out.

budding

Tags:virology, capsid, budding

Source:https://youtu.be/3olXpSqEOmY

   Isaac Asimov: Life and Energy   

Glycoproteins

Glycoproteins are structural components of viral membranes. They have internal and external parts. The external part is involved in attachment to specific cells to infect.

glycoprotein

Tags:virology, capsid, structure, glycoprotein

Source:https://youtu.be/3olXpSqEOmY

   Isaac Asimov: Life and Energy   

Glycoproteins Orientation

Glycoproteins can be oriented vertically as well as horizontally on the surface of the membrane.

glycoprotein orientation

Tags:virology, capsid, structure, glycoprotein

Source:https://youtu.be/3olXpSqEOmY



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