Week 11

Question 1

What is a virus

Answer 1

• Viral particles consist of multiple nucleic acids (DNA or RNA) enclosed in a protein coat and often other layers as well.
• Such additional layers can be simple or complex containing carbohydrates, lipids, and proteins

Question 2

Phases of virus

Answer 2

• Extracellular phase-virions
• Intracellular phase-replicating nucleic acids

Question 3

Extracellular phase

Answer 3

• Virions are complete, whole viruses (both nucleic acids and capsid).
• Virions contain few or no enzymes.
• Can’t reproduce independently of living cells.

Question 4

Intracellular phase

Answer 4

• Induce the host cell’s metabolism to produce virion components.
• Eventually virions (complete virus particles) are released from the host cell.

Question 5

How do viruses differ from living cells?

Answer 5

• Simple acellular organization.
• The presence of DNA or RNA in the same virion – never both simultaneously!
• The inability to reproduce independently from their host cells – can’t undergo normal cell division such as prokaryotes and eukaryotes. They are thus, called
  “obligate intracellular parasites”.

Question 6

Virion size

Answer 6

10nm-400nm
V small

Question 7

Morphological Types of Capsids and Virion Structures

Answer 7

1. Icosahedral capsids
2. Helical capsids
3. Membrane-like capsules
4. Complex viruses

Question 8

Helical and icosahedral capsids

Answer 8

*Macromolecular structures consisting of many copies of one or more types of
protein sub-units or “protomers”.
*Small part of the viral genome codes for the capsid proteins.
*After the complete formation of protomers in host cells, they spontaneously
associate with one another to form the capsid

Question 9

What is self assembly

Answer 9

After the complete formation of protomers in host cells, capsids spontaneously
associate with one another to form the capsid
*not influenced by external factors

Question 10

Complex viruses

Answer 10

Contain genes coding for special factors that are required for the assembly of the virion – not incorporated into the virion itself.

Question 11

Role of Receptors in Viral Infection

Answer 11

*The distribution of these receptor proteins is key to many viruses’ host specificity – viruses
only affect cells whose receptors they can bind to.
* Virions bind to essential receptor proteins vital for cell functioning
* Some surface receptor proteins bind to hormones.
*Many surface receptor proteins are immunoglobulin-type molecules that play a vital role in immune response and during cell-to-cell interactions.

Question 13

Linear, single-stranded, negative strand

Answer 13

Complementary to the positive strand but cannot be used directly to produce proteins during translation.

Question 14

Viral reproduction steps

Answer 14

Adsorption
Penetration and unceasing
Synthesis
Assembly
Release of mature virion

Question 15

Adsorption

Answer 15

Virion attaches to surface structures of the host cell

Question 16

Penetration and uncoating

Answer 16

Virus enters the host cell and its capsid is removed

Question 17

Synthesis

Answer 17

Virus hijacks host cell enzymes and reproduction machinery to synthesise viral proteins and nucleic acid.

Question 18

Assembly

Answer 18

Newly produced proteins and nucleic acids are used to assemble new viruses in the host cell

Question 19

Release of mature virion

Answer 19

Host cell may be destroyed or releases the virions via small buds that appear on the host cell surface

Question 21

Structural proteins

Answer 21

*The binding site on the virion consists of structural proteins on the surface of the capsid.
*These proteins are strategically placed to often avoid antibodies produced by the host yet still have access for binding to projections of the host cell

Question 22

Glycoproteins

Answer 22

Glycoproteins on the membraneous envelope of the virus also aid in
attachment and penetration