L4 Viral morphology and replication

Question 1

What is the common size for viruses? They have to be observed

Answer 1

0.02-0.03 uM (nanometer)

Question 2

What is the difference between virion and virus?

Answer 2

Virion: extracellular state
Virus: intracellular state/ capsid removed

Question 3

Which of the following are correct about viruses?
A. They are dependent on living cells for replication
B. They are non-motile
C. They are obligate intracellular
D. They are acellular
E. They have nucleus
F. They lack organelles for metabolism
G. They can redirect host cells as synthetic machinery

Answer 3

All except E

They do not have nucleus

Question 4

Can virus have both DNA and RNA?

Answer 4

No, only DNA or RNA

Question 5

List the differences between DNA and RNA viruses. (4)

Answer 5

1. Strand
   DNA: DS (double strand) more common
   RNA: SS (single strand more common
2. Site of replication
   DNA: in the nucleus
   RNA: in cytoplasm
3. Transcription
   DNA: must transcribe DNA > RNA
   RNA: No need to transcribe to RNA
4. Stability
   DNA: more stable: DNA polymerase has proof-reading
   RNA: less stable: RNA polymerase and reverse transcriptase have no proof-reading

Question 6

Functions of virus genome include integration and tumor formation. Briefly describe.

Answer 6

• Integration: dsDNA resembles human DNA and can be integrated into host DNA
• Tumor information: oncoprotein, e.g. HPV E6, E7 proteins (cut and ligate > when human DNA replicates > replicate too)

Question 7

What is a caspid of a virus?

Answer 7

Protein coat formed by capsomeres (repearing protein subunits)

Question 8

Which of the following are functions of caspid?
A. Protect nucleic acid form degradation
B. Receptor bidngin for naked virus
C.  Facilitate entry into host cell 
D. Marker for diagnosis
E. Antigen to stimulate immune response 
F. Component of vaccine

Answer 8

All of the above

Question 9

What are the differences of icosahedral and helical caspids? Give examples of each caspid too. (4)

Answer 9

Icosaheral: = cubic, spherical, DNA/RNA
e.g. Herpesvirus, HIV, Adenovirus, Papillomavirus
Helical: = rod like, RNA only
e.g. Influenza, rabies, Ebolavirus

Question 10

Enveloped virus contains envelop enclosing the viral protein core. Why can they be killed by using disinfectants?

Answer 10

The envelop is acquired by budding through host plasma membrane, thus it is a lipid bilayer membrane with high lipid content

Question 11

Which of the following about enveloped virus are correct?
A. They have viral specific surface glycoproteins as receptor-binding proteins
B. They are susceptible to heat
C. They are susceptible to detergents
D. They are targets of antivirals and vaccines
E. Naked virus are more resistant to heat and detergents

Answer 11

All of the ablve!

Nearly all gastroeneteritis virus like norovirus are naked virus (not enveloped), thus cannot be killed by alcohol.

Question 12

How many layers of proteins are there in Rotavirus?

Answer 12

3

Question 13

Name the targets for antiviral and vaccines in different types of viral proteins. (2) (naked and enveloped)
What are the targets of drugs in viral proteins? (1)

Answer 13

Naked virus: caspid proteins
Enveloped virus: surface glycoproteins
Enzymes are the target of drugs

Question 14

What is ressortment in viral genome?

Answer 14

Virus with segmented genomes can exchange whole segment of genetic information creating novel features for the next generation.

Question 15

DNA virus can be divided into enveloped and naked viruses. Give examples of each category of virus.

Answer 15

Enveloped: Herpes (HSV1), Hepadna (HBV)
Naked: Papillomavirus (e.g. HPV), Adenovirus

Question 16

RNA viruses can be divided into double and single stranded viruses. Give the only example of virus that is double-stranded (naked too).

Answer 16

Reovirus (e.g. Rotavirus)

Question 17

Single-stranded RNA virus can be further divided into positive and negative-stranded viruses.
Negative stranded, enveloped Orthomyoxiviridae and Paramyxoviridae are examples. Give an example for each of them.

Answer 17

Orthomyoxiviridae: Influenza
Paramyxoviridae: RSV, parainfluenza

Question 18

Single-stranded, positive-stranded, enveloped RNA:
A. Flavivirus e.g. Dengue, Japanese encephalitis
B. Retrovirus e.g. HIV
C. Calicivirus e.g. Norovirus

Answer 18

A and B only

C: Should be Single-stranded, positive-stranded, NAKED RNA

Question 19

Viral replication cycle:
A. (1)Attachment of virus to host cell receptors determines what ell can be infected
B. (2)All viruses penetrate the host cells by the same way
C. (3) Virus then release nucleic acid into the nucleus or cytoplasm of the host cell - uncoating
D. (4) Only mRNA are formed furing macromolecular synthesis

Answer 19

A and C
only

B: by 3 different ways
D: Early mRNA and protein synthesis: proteins are also formed

• Proteins to shut off host cell
• Proteins to replicate viral genome if needed

> Replication of the viral genome
Late mRNA and protein synthesis: structural proteins are formed

Question 20

At the stage of macromolecular synthesis in viral replication cycle, what happens in during the replication of genome?

Answer 20

Replication of the viral genome +/- integrate into host DNA +/- transcription for viral mRNA > translation of mRNA in the cytoplasm

Question 21

After macromolecular synthesis, there is postranslational modification of proteins, then the assembly of new virus particles to caspid. What happens in this stage?

Answer 21

Encapsulation of nucleic acid > insertion of envelop proteins into plasma membrane

Question 22

The release of newly formed virus are different in naked and enveloped virions, briefly describe.

Answer 22

Naked virions: By lysis of host cells > no persistent productive infections

Enveloped virus: By budding, cell senescence, but may produce a low level of virus for years e.g. in chronic HepB

Question 23

In retrovirus replication cycle e.g. HIV, (it is an enveloped ssRNA virus), what are involved?
A. Reverse transcriptase
B. Protesase
C. Integrase

Answer 23

All of the above