Lecture 16. Viral Structure

Question 1

What is the structure of viruses?

Answer 1

Nucleic acid (DNA or RNA)
Protein coat (capsid)
Viral envelope (Derived from host cell)
Viral attachment proteins

Question 2

What is the cellular receptor of SARS-CoV-2?

Answer 2

ACE2

Question 3

What is a capsid?

Answer 3

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

Question 4

What is the viral envelope?

Answer 4

Envelope is bilayer phospholipid membrane derived mainly from the host cell

Question 5

What is a virion?

Answer 5

The complete virus particle

Question 6

What information is encoded in the viral genome?

Answer 6

Nucleic acid (DNA or RNA)
Structural proteins (capsid proteins, VAPs…)
Non-structural proteins

Question 7

What is not encoded in viral genomes?

Answer 7

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

Question 8

What is the capsomere?

Answer 8

Subunit of the capsid
Smallest morphological unit visible with an electron microscope

Question 9

What shape are most viral particles?

Answer 9

Either rod or round

Question 10

How are round viruses arranged?

Answer 10

Identical protein subunits are arranged in icosahedral symmetry

Question 11

How are rod viruses arranged?

Answer 11

Rod viruses are arranged in helical symmetry

Question 12

How is metastability achieved?

Answer 12

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

Question 13

What makes a virus structure unstable?

Answer 13

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

Question 14

What can some viruses self-assemble into?

Answer 14

Virus-like particles (VLPs)

Question 15

What symmetry can capsids have?

Answer 15

Helical
Icosahedral
Complex

Question 16

What is a subunit?

Answer 16

Single folded polypeptide chain

Question 17

What is a structural subunit?

Answer 17

Unit from which the capsid is built-one or more subunit

Question 18

What is an icosahedron?

Answer 18

20 faces – each an equilateral triangle
30 edges – each an interface between 2 faces
12 vertices – each a point where 5 faces meet

Question 19

What are icosahedral capsids made of?

Answer 19

60 identical protein subunits

Question 20

How are bigger icosahedral viruses built?

Answer 20

By adding more subunits
Pentons and hexons

Question 21

What viruses have icosahedral symmetry?

Answer 21

Poliovirus
Rotavirus
Varicella-zoster virus
Reovirus

Question 22

What does the herpes simplex virus capsid contain?

Answer 22

Holes for entry and exit of DNA

Question 23

What is an example of a virus that has helical symmetry?

Answer 23

Tobacco Mosaic Virus (TMV)

Question 24

What determines the length of viruses with helical symmetry?

Answer 24

Length of nucleic acid

Question 25

What determines the width of viruses with helical symmetry?

Answer 25

Size and packaging of protein subunits

Question 26

What are examples of viruses that have complex symmetry?

Answer 26

Poxviruses and some bacteriophages

Question 27

What does the presence of a viral envelope confer?

Answer 27

Instability on the virus