Virology Flashcards
Smallest pathogenic virus
Parvovirus
Largest pathogenic virus
Latest genome of a pathogenic virus is of
Pox viruses 300-400 nm Seen under light microscope Has complex symmetry Cytoplasmic replication
Pox virus
Smallest genome of a pathogenic virus is of
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
Families of DNA viruses
Enveloped viruses are: 1. Herpes 2. Hepadna 3. Pox Non enveloped viruses are: 4. Parvo 5. Adeno 6. Papilloma 7. Polyoma
Why do pox viruses have cytoplasmic replication
Pox viruses have their own DNA dependent RNA polymerase
So they make their own RNA
Characteristics of DNA viruses
- All have ds DNA (except parvovirus)
- Nuclear replication (except pox viruses)
- Icosahedral symmetry (except pox viruses)
- Transfection of naked nuclei acid is infectious to host cell (except pox and hepadna)
RNA viruses characteristics
- 15 families
- Most are enveloped
- All have ss RNA (except reo)
- Negative stranded or positive stranded
- Some have segmented genome (genetic reassortment)
- Cytoplasmic replication (except MOR)
- Transfection of naked nucleic acid is infectious to host cell in all positive stranded (except retro)
Non enveloped RNA viruses
P. Picorna A. Astro R. Reo (ds RNA) C. Calici H. Hepe E. D.
Negative stranded RNA viruses
Always Bring D Polymerase Or Fail Replication A. Arena B. Bunya D. Delta (no helical symmetry) P. Paramyxo O. Orthomyxo F. Filo R. Rhabdo
RNA viruses with segmented genome
R. Reo 10-12
O. Orthomyxo 7-8
B. Bunya 3
A. Arena 2
RNA viruses with helical symmetry
A. Arena B. Bunya C. Corona (positive-stranded) P. Paramyxo O. Orthomyxo F. Filo R. Rhabdo
RNA viruses which do not have cytoplasmic replication
M. Measles (paramyxo)
O. Orthomyxo
R. Retroviruses
Examples of receptors to which viruses bind for replication
For EBV - CD21/ CR-2
For Parvo - P blood group antigen
Steps of replication of viruses
- Binding to receptors
- Absorption into host cell
- Uncoating
- Synthesis of vital components
Early mRNA➡️ early enzymes for replication ➡️ genome copies ➡️ late mRNA ➡️ late proteins (structural) - Assembly
- Release - budding/lysis
Baltimore classification
Based on virus replication
- ds DNA
- ss DNA (parvo)
- ds RNA (reo)
- ss RNA +ve stranded
- ss RNA -ve stranded
- ss RNA +ve stranded replicating through a DNA intermediate
- ds DNA replication through a RNA intermediate (HBV)
Viruses which do not multiply in lab rats
Coxsackie
Arbo viruses grow in suckling mice
Methods of cultivation of viruses
- Lab animals (usually mouse)
- Hen’s egg
- 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
Viruses growing in various parts of hen’s egg
1. Chorioallantoic membrane: Pox viruses except Molluscum 2. Amniotic cavity: Primary isolation of myxoviruses 3. Allantoic cavity: Myxoviruses after adaptation 4. Yolk sac: Arboviruses
Examples of 3° or continuous cell lines
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
