MICROPARA - MODULE 3

Virology

Study of viruses and virus-like agents

Virus

Acellular microorganism that requires a host cell to replicate; consists of nucleic acid and protein coat

Obligate Intracellular Parasite

Organisms like viruses that can multiply only inside living host cells

Virion

Complete, fully developed viral particle that is infectious

Capsid

Protein coat surrounding the nucleic acid of a virus

Capsomere

Protein subunit that makes up the capsid

Nucleocapsid

Combination of viral nucleic acid and capsid

Envelope

Lipid bilayer membrane that surrounds some viruses; derived from host cell membrane

Spikes

Carbohydrate-protein projections from viral envelope used for attachment to host cell

Helical Virus

Virus with rod-shaped capsid forming a helical structure (e.g., tobacco mosaic virus)

Polyhedral Virus

Virus with many-sided capsid; most common is icosahedral (20 faces, 12 corners)

Complex Virus

Virus with complicated structures (e.g., bacteriophage with head, sheath, tail fibers)

Bacteriophage

Virus that infects bacteria

Host Range

The spectrum of host cells a virus can infect

Tropism

Specificity of a virus for a particular host tissue or cell type

Lytic Cycle

Viral replication cycle that ends with host cell lysis and release of new virions

Lysogenic Cycle

Viral DNA integrates into host genome (prophage) and replicates without immediately killing the host

Prophage

Viral DNA integrated into bacterial chromosome during lysogeny

Induction

Process by which a prophage exits the host chromosome and enters the lytic cycle

One-Step Growth Curve

Experimental demonstration of virus replication with eclipse, maturation, and release phases

Burst Size

Number of virions released from a single infected host cell

Eclipse Period

Time after infection when viral components are being synthesized but no infectious virions are detected

Maturation Phase

Assembly of viral components into complete virions

Acute Infection

Viral infection with rapid onset, short duration, and quick resolution (e.g., influenza)

Persistent Infection

Long-term infection where virus remains in host for extended period

Latent Infection

Viral infection that remains dormant in host and can reactivate (e.g., herpesvirus)

Chronic Infection

Continuous low-level virus production without killing the host (e.g., hepatitis B)

Oncogenic Virus

Virus that can cause cancer by integrating into host genome and altering growth regulation

Proto-Oncogene

Normal gene that can become an oncogene when mutated or influenced by viruses

Oncogene

Gene that transforms normal cells into cancerous cells

Transformation

Conversion of normal host cells into tumor cells by viral infection

Prion

Infectious protein particle lacking nucleic acid; causes neurodegenerative diseases (e.g., mad cow disease)

Viroid

Short piece of naked RNA without protein coat; causes plant diseases

Cultivation of Viruses

Grown in living animals, embryonated eggs, or cell cultures

Primary Cell Culture

Culture derived directly from animal tissues; limited life span

Continuous Cell Line

Cell culture that can be maintained indefinitely (e.g., HeLa cells)

Cytopathic Effect

Visible changes or damage in host cells due to viral infection

Plaque

Clear zone in bacterial lawn caused by bacteriophage lysis of host cells

Plaque-Forming Unit (PFU)

Measure of the number of infectious virus particles

Hemagglutination

Viral clumping of red blood cells; used for virus quantification

Viral Identification

Methods include cytopathic effects, serological tests, and nucleic acid analysis

Serological Tests

Use of antibodies to detect viral antigens or host antibodies to viruses

Nucleic Acid Amplification

Techniques like PCR used to detect viral genomes

Retrovirus

RNA virus that uses reverse transcriptase to make DNA from RNA template (e.g., HIV)

Reverse Transcriptase

Enzyme that synthesizes DNA from RNA template

HIV

Human Immunodeficiency Virus; retrovirus that causes AIDS

Provirus

Viral DNA integrated into host cell genome in eukaryotes

Antiviral Drugs

Compounds that inhibit viral replication by targeting enzymes or steps of replication cycle

Interferons

Host proteins that inhibit viral replication and protect neighboring cells

Viral Latency

Virus remains inactive inside host cell and may reactivate under stress

Viral Receptors

Specific molecules on host cell surface used by viruses for attachment and entry

Host Cell Susceptibility

Determined by presence of receptors and ability to support viral replication