Virology 1

Question 1

What are viruses?

Answer 1

Viruses are non-cellular organisms:
➢ consists of either DNA or RNA that is surrounded by a protein coat
➢ “invisible” by light microscopy with sizes ranging from 20-400 nm
➢ infect any living organism e.g., vertebrates, invertebrates, plants, bacteria and fungi
➢ obligate “intracellular parasites” that require a host cell for replication
➢ individual viral components self-assemble into a virion
➢ virion is a complete infectious form of virus outside the host cell (extracellular)

Question 2

Viral genomes can be…

Answer 2

Viral genomes can be:
➢ single stranded (ss), double stranded (ds), linear, circular, segmented, haploid or
diploid

Most viruses are structurally simple, however, some viruses have more complex structure

• The basic biophysical and biochemical rules of the viral structure and assembly are same for all viruses

Question 3

What are the parts of the viral structure?

Answer 3

Question 4

What is a viral caspid?

Answer 4

• The virus capsid serves to protect the nucleic acid genome. It is held together by non-covalent, reversible hydrophobic or hydrogen bonds
• Consists of single or several different subunits (capsomeres) that have variable sizes, have identifiable domains and symmetry

Question 5

What are the caspid proteins functions in virus caspid?

Answer 5

Capsid proteins have various functions:

Define tissue or species specific transmission by interaction with host receptors to facilitate the host cell entry

Interact with the viral nucleic acid for packaging/ assembling the virus Assist in viral and/or host gene regulation

Evade/block host immune system, and other functions….

Question 6

What are the three general forms of nucleocapsid morphology?

Answer 6

Three general forms of nucleocapsid morphology:

➢ icosahedral (roughly spherical)
➢ helical
➢ complex (nonsymmetrical)

Question 7

Describe the structure of Icosahedral caspid

Answer 7

Question 8

Describe the helical capsid of viruses

Answer 8

Question 9

Describe the complex capsid of viruses

Answer 9

Question 10

What are the “other” types of capsid structures?

Answer 10

Question 10

What are the “other” types of capsid structures?

Answer 10

Question 11

What’s the significance of a viral envelope?

Answer 11

Question 11

What’s the significance of a viral envelope?

Answer 11

Question 12

What’s the significance of enveloped viruses?

Answer 12

• Viral nucleocapsid is surrounded by a lipoprotein membrane derived from host cell membrane (e.g. measles virus) or nuclear (herpesvirus) or other internal membranes and contains virus specific glycoproteins
• They are sensitive to inactivation by organic solvents (alcohol, chloroform, ether, etc.) detergents, drying, acid, heat.
• They are usually transmitted by secretions, large droplets, blood or sexual contact e.g., measles virus
• Enveloped viruses are usually spherical or pleomorphic in shape except rhabdovirus (rabies, bullet shaped) and poxvirus (smallpox, complex

Question 13

What’s the significance of non-enveloped (naked) virus?

Answer 13

Question 14

What are viral attachment proteins (VAP) or peplomers?

Answer 14

 Viral attachment proteins (VAP) or peplomers – facilitate host cell entry, e.g., hemaglutinin (HA) on influenza virus which binds erythrocytes, VAP on Epstein-Barr virus (EBV) binds C3d receptor (CR2) on B cells

Question 15

What’s the significance of viral polymerase?

Answer 15

Viral polymerase present within the genome of viruses and involved in transcription and replication of viral genome

Question 16

What are viral matrix proteins?

Answer 16

Matrix proteins present between the nucleocapsid and envelope, stabilize the organization of viral glycoprotein, directs the viral genome to intracellular sites of viral assembly, facilitate virus assembly and budding

Question 17

What are the phase proteins?

Answer 17

• Depending on the virus and its expression pattern, viral proteins are divided into immediate early phase proteins; early phase proteins, and late phase proteins

Question 18

How are viruses classified/nomenclature?

Answer 18

Viruses are classified using a combination of characteristics, including the following:

1. Morphology: size, shape, presence of envelope, etc.
2. Physicochemical properties: thermal stability, detergent stability,
   molecular mass, etc.
3. Genome: size, type of nucleic acid, strandedness, etc.
4. Proteins: number, size, sequence, etc.
5. Lipids: content, character, etc.
6. Carbohydrates: content, character, etc.
7. Genome organization and replication: strategy of replication, number and
   position of open reading frames, transcriptional and translational
   strategies, site of virion assembly and release.
8. Antigenic properties: serological relationships.
9. Biological properties: Host range, mode of transmission, pathogenicity,
   tissue tropisms, geographic distribution, etc.

Question 19

What is the ICTV ?

Answer 19

Question 20

What are the types of viruses, give an example of each?

Answer 20