- Virus is an obligate intracellular parasite containing genetic material surrounded by proteins
- Not living organisms, cannot produce energy or synthesize proteins independently, host cell machinery is needed
- Viruses that infect bacteria are called bacteriophages
Difference between Naked Virus and Enveloped Virus
| Properties | Enveloped | Naked |
| Environmental stability | Are destroyed by acids, detergents and drying (easily die) | Stable to temperaure, acids, proteases, disinfectants and drying |
| Release from cell | Budding | Lysis |
| Spread to host | Spreads in large droplets, secretions, transplanted organs, blood transfusions | Spread easily by direct contact, dust, small air droplets |
| Stability outside cells | Must stay wet | Can dry out and retain infectivity |
| Effective immune respone | May need antibody and cell mediated immunity for protection | Antibodies are sufficient |
Difference between bacteria and viruses
| Virus
|
Bacteria |
| Obligate intracellular parasites | Free living, can be parasitic |
| No ribosomes | Has ribosomes |
| DNA or RNA, not both | DNA and RNA |
| Need electronic microscopes | Seen in light microscopes |
| 10-100 genes | 100-1000 genes |
| Tangled phylogeny | Natural phylogeny |
Baltimore Classification of Viruses
Replication of viruses
All RNA viruses replicate in the cytoplasm except Orthomyxoviruses and Retroviruses that have replicative stages in nuclei
All DNA viruses replicate in the cytoplasm except Poxviruses that can replicate in the cytoplasm.
DentMistry 