Questions
3–5 questions in university papers
Difficulty
Medium
Importance
High yield for microbiology and clinical pharmacology sections
Overview
Virology is the study of viruses, submicroscopic infectious agents that replicate only inside living host cells. Understanding viral morphology, classification, and life cycles is essential for clinical diagnostics and vaccine development. Mastery of this topic allows students to connect host-pathogen interactions with pharmacological antiviral interventions.
Virus Structure and Classification
Viruses consist of a nucleic acid genome encapsulated by a protein shell called a capsid, sometimes surrounded by a lipid envelope. They are classified based on the Baltimore system, which categorizes viruses by their method of mRNA synthesis and genome type.
- Nucleic acid: Either DNA or RNA, never both
- Capsid symmetry: Helical, Icosahedral, or Complex
- Enveloped vs. Non-enveloped viruses
- Baltimore classification groups I through VII
- Viral spikes consist of glycoproteins for attachment
Viral Replication Cycle
Viral replication is a multi-step process that hijacks host machinery to produce viral components. The cycle is consistent across most animal viruses and is a primary target for chemotherapeutic drugs.
- Attachment (Adsorption) to host cell receptors
- Penetration via endocytosis or membrane fusion
- Uncoating to release the viral genome
- Biosynthesis of viral proteins and genome
- Assembly and maturation of viral particles
- Release via budding or host cell lysis
Common Pathogenic Viruses
Various families of viruses cause human diseases, differing in their transmission routes and target tissues. Understanding the specific pathology of major families is crucial for clinical assessments.
- Retroviridae: HIV, contains reverse transcriptase
- Orthomyxoviridae: Influenza, segmented genome
- Hepadnaviridae: Hepatitis B, DNA virus with RT activity
- Coronaviridae: SARS-CoV-2, positive-sense ssRNA
- Picornaviridae: Poliovirus, Rhino-virus
Antiviral Basics
Antiviral drugs function by inhibiting specific steps in the viral replication cycle without damaging host cell function. Resistance often develops through mutations in viral enzymes like polymerase or proteases.
- Nucleoside analogues (e.g., Acyclovir, Zidovudine)
- Protease inhibitors to prevent viral maturation
- Entry inhibitors preventing membrane fusion
- Neuraminidase inhibitors (e.g., Oseltamivir)
- Interferons as host immune-modulators
Exam Tip
Always draw a simple labeled diagram of the viral life cycle; it provides significant credit in descriptive answers even if the text explanation is concise.
Common Mistakes
- Confusing the Baltimore Classification system categories with taxonomic families
- Failing to mention the difference between naked (non-enveloped) and enveloped virus stability
- Misidentifying reverse transcriptase as an enzyme present in all RNA viruses
More Revision Notes
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