Virology

Question 1

Smallest pathogenic virus

Answer 1

Parvovirus

Question 2

Largest pathogenic virus

Latest genome of a pathogenic virus is of

Answer 2

Pox viruses 
300-400 nm
Seen under light microscope
Has complex symmetry
Cytoplasmic replication

Pox virus

Question 3

Smallest genome of a pathogenic virus is of

Answer 3

Hepatitis B virus HBV (3.2 kbp)
It’s envelope is developed from the ER

Note:
HDV (smaller but not independent replication) 1.7 kbp

Question 4

Families of DNA viruses

Answer 4

Enveloped viruses are:
1. Herpes 
2. Hepadna
3. Pox
Non enveloped viruses are:
4. Parvo 
5. Adeno
6. Papilloma
7. Polyoma

Question 5

Why do pox viruses have cytoplasmic replication

Answer 5

Pox viruses have their own DNA dependent RNA polymerase

So they make their own RNA

Question 6

Characteristics of DNA viruses

Answer 6

1. All have ds DNA (except parvovirus)
2. Nuclear replication (except pox viruses)
3. Icosahedral symmetry (except pox viruses)
4. Transfection of naked nuclei acid is infectious to host cell (except pox and hepadna)

Question 7

RNA viruses characteristics

Answer 7

1. 15 families
2. Most are enveloped
3. All have ss RNA (except reo)
4. Negative stranded or positive stranded
5. Some have segmented genome (genetic reassortment)
6. Cytoplasmic replication (except MOR)
7. Transfection of naked nucleic acid is infectious to host cell in all positive stranded (except retro)

Question 8

Non enveloped RNA viruses

Answer 8

P. Picorna
A. Astro
R. Reo (ds RNA)
C. Calici
H. Hepe 
E. 
D.

Question 9

Negative stranded RNA viruses

Answer 9

Always Bring D Polymerase Or Fail Replication
A. Arena
B. Bunya
D. Delta (no helical symmetry)
P. Paramyxo 
O. Orthomyxo
F. Filo
R. Rhabdo

Question 10

RNA viruses with segmented genome

Answer 10

R. Reo 10-12
O. Orthomyxo 7-8
B. Bunya 3
A. Arena 2

Question 11

RNA viruses with helical symmetry

Answer 11

A. Arena
B. Bunya
C. Corona (positive-stranded)
P. Paramyxo 
O. Orthomyxo
F. Filo
R. Rhabdo

Question 12

RNA viruses which do not have cytoplasmic replication

Answer 12

M. Measles (paramyxo)
O. Orthomyxo
R. Retroviruses

Question 13

Examples of receptors to which viruses bind for replication

Answer 13

For EBV - CD21/ CR-2

For Parvo - P blood group antigen

Question 14

Steps of replication of viruses

Answer 14

1. Binding to receptors
2. Absorption into host cell
3. Uncoating
4. Synthesis of vital components
   Early mRNA➡️ early enzymes for replication ➡️ genome copies ➡️ late mRNA ➡️ late proteins (structural)
5. Assembly
6. Release - budding/lysis

Question 15

Baltimore classification

Answer 15

Based on virus replication

1. ds DNA
2. ss DNA (parvo)
3. ds RNA (reo)
4. ss RNA +ve stranded
5. ss RNA -ve stranded
6. ss RNA +ve stranded replicating through a DNA intermediate
7. ds DNA replication through a RNA intermediate (HBV)

Question 16

Viruses which do not multiply in lab rats

Answer 16

Coxsackie

Arbo viruses grow in suckling mice

Question 17

Methods of cultivation of viruses

Answer 17

1. Lab animals (usually mouse)
2. Hen’s egg
3. Tissue culture:
   A. Cell lines: most common
   1° Fresh cells like Monkey kidney
   2° Diploid, capable of passage 30-40 times, like WI-38 (human embryonic lung cell), HL-8, MRC-5
   3° Indefinite passage (transformed or cancerous) like HeLa, Hep-2,…
   B. Organ culture
   C. Explant culture

Question 18

Viruses growing in various parts of hen’s egg

Answer 18

1. Chorioallantoic membrane:
 Pox viruses except Molluscum
2. Amniotic cavity:
 Primary isolation of myxoviruses
3. Allantoic cavity:
 Myxoviruses after adaptation
4. Yolk sac:
 Arboviruses

Question 19

Examples of 3° or continuous cell lines

Answer 19

HeLa: human carcinoma of cervix cell line
Hep2: human epithelioma of larynx cell line
KB: human epithelioma of nasopharynx cell line
McCoy: human synovial cell carcinoma cell line
BHK: baby hamster kidney cell line