Introduction to Virology - Virology | Lecture Notes

Overview of virology as a branch of microbiology focusing on the study of viruses, their structure, classification, replication cycle, and host interactions.

Introduction to Virology – Study Notes

1. What Is Virology?

Definition: Branch of microbiology that deals with viruses – their structure, classification, replication, evolution, and the diseases they cause.
Scope:
- Basic virology (virus biology, life cycle)
- Clinical virology (diagnosis, treatment, prevention)
- Molecular virology (genome manipulation, vaccine design)
- Environmental/animal virology (zoonoses, viral ecology)

2. Fundamental Concepts

Concept	Key Points
Virus	Submicroscopic infectious particle consisting of nucleic acid (DNA or RNA) surrounded by a protein coat (capsid); some have a lipid envelope.
Obligate intracellular parasite	Cannot replicate outside a host cell; relies on host machinery for transcription, translation, and energy.
Virion vs. Virus	Virion: complete, extracellular infectious particle. Virus: the replicative form inside the host cell (genome + associated proteins).
Host range	Spectrum of species/cell types a virus can infect; determined by receptor binding and intracellular factors.
Tropism	Preference for specific tissues or cell types (e.g., neurotropism, hepatotropism).

3. Virus Structure

Genomic Nucleic Acid
- DNA viruses: dsDNA (e.g., Herpesviridae), ssDNA (e.g., Parvoviridae)
- RNA viruses: +ssRNA (e.g., Picornaviridae), –ssRNA (e.g., Orthomyxoviridae), dsRNA (e.g., Reoviridae), ssRNA‑RT (retroviruses), dsDNA‑RT (hepadnaviruses)
Capsid
- Protein subunits (capsomeres) assemble into icosahedral, helical, or complex symmetry.
- Provides protection and determines antigenicity.
Envelope (optional)
- Lipid bilayer derived from host membranes, embedded with viral glycoproteins (spikes) that mediate attachment and entry.
- Enveloped viruses are generally more sensitive to detergents, heat, and desiccation.
Accessory Structures
- Matrix proteins: scaffold between capsid and envelope.
- Tegument (herpesviruses): layer of proteins that modulate host response.
- Enzymes packaged in virion: polymerases (e.g., RNA‑dependent RNA polymerase), integrase, reverse transcriptase.

4. Virus Classification (ICTV System)

Level	Example	Basis of Classification
Realm	Riboviria	Replication strategy (RNA viruses)
Kingdom	Orthornavirae	Genome type & replication
Phylum	Pisuviricota	Polyprotein processing
Class	Alphaherpesviridae	Morphology, genome organization
Order	Mononegavirales	Non‑segmented, negative‑sense RNA
Family	Flaviviridae	Genome size, envelope, replication
Genus	Flavivirus	Sequence similarity, vector
Species	Dengue virus	Host range, pathogenicity

Key point: Classification reflects both evolutionary relationships and practical features (e.g., genome type, replication mechanism).

5. Viral Replication Cycle (General Steps)

Topic Concept Map

Click any prompt to explore this topic interactively with your AI Tutor:

Explain in simple terms Give me 3 practice exam questions Summarize key principles in 5 points

Introduction to Virology

Viral Structure and Classification

Upgrade

Viral Replication Cycle

Upgrade

Host-Virus Interactions

Upgrade

Viral Pathogenesis

Upgrade

Antiviral Therapeutics

Upgrade

Viral Epidemiology

Upgrade

Emerging Viral Infections

Upgrade

Viral Evolution and Genetic Variability

Upgrade