Module Six: Viruses and Acellular Pathogens

This flashcard set covers the introduction to viruses, their structure, replication cycles, detection methods, other acellular pathogens (viroids/prions), immune defenses, and various classes of antiviral medications.

Viruses

Acellular, non-living obligate intracellular parasites that must be inside a host cell to replicate.

Virion

An individual virus particle with a simple structure composed of a nucleocapsid.

Nucleocapsid

The combination of the viral nucleic acid (genome) and its protein coat (capsid).

Viral Genome

The genetic material of a virus, which unlike living cells, can be either $DNA$ or $RNA$.

Capsomers

Viral encoded protein building blocks that assemble to form the capsid.

Envelope

A phospholipid bilayer surrounding the capsid that is host-derived, or picked up from host cells upon release.

Spikes (Peplomers)

Viral derived protein structures used to attach the virus to host cell receptors.

Hemagglutinin ($H$)

A specialized spike used to attach the influenza virus to a host cell.

Neuraminidase ($N$)

A specialized spike found on influenza viruses used for identification and viral release.

Helical Virus

A virus shape where capsomers are arranged in a tube or barrel shape, with the nucleic acid length determining the cylinder length.

Icosahedron

A capsid shape composed of $20$ equilateral triangles, providing the virus with $20$ faces or facets.

Complex Viruses

Viruses with a combination of shapes, such as a bacteriophage which has an icosahedral head and a helical sheath.

Bacteriophage

A specific group of viruses that infect bacterial cells.

Lytic Cycle

The five-step infection process of a phage: attachment, penetration ($DNA$ injection), biosynthesis, maturation (self-assembly), and lysis (release).

Lysogeny

A viral cycle where the phage genome integrates into the bacterial genome and is passed to offspring through replication.

Induction

The process where phage $DNA$ is excised from the host genome, typically due to stress, to begin the lytic cycle.

Tropism

The affinity of animal viruses for a particular type of cell or tissue, such as hepatocytes in liver tissue.

Fusion

A penetration method for enveloped animal viruses where the viral envelope merges with the host cell membrane.

Uncoating

The step in the animal virus cycle where the protein capsid is removed to release the genetic material.

Budding

A release method for enveloped viruses where the particle pushes out the host membrane and is pinched off, taking the envelope with it.

Reverse Transcription

The process where viral $RNA$ is transcribed into $DNA$, a characteristic step for retroviruses like HIV.

Reverse Transcriptase

A specialized enzyme required by retroviruses to convert $RNA$ into $DNA$.

Dorsal Root Ganglion

The location outside the spinal cord where the Varicella zoster virus lies dormant after a chickenpox infection.

Dermatome

A region of skin served by a particular spinal or cranial nerve where shingles infections typically erupt.

In Vivo Cultivation

Methods of growing viruses in living organisms, such as animals or embryonated chicken eggs.

In Vitro Cultivation

The growth of viruses in an artificial environment, such as cell or tissue cultures in a flask or test tube.

Cytopathic Effects (CPEs)

Observable tissue changes caused by viral infection, such as canine distemper virus causing cells to have two nuclei.

Polymerase Chain Reaction (PCR)

A nucleic acid amplification test used to make millions of copies of a specific viral genetic sequence for detection.

Enzyme Immunoassay (EIA)

A detection method using enzyme-linked antibodies to create a sandwich assay that triggers a chromogenic (color change) reaction.

Viroids

Plant pathogens composed only of a small loop of single-stranded $RNA$ that cause crop failures.

Prions

Acellular pathogens consisting of abnormal, misfolded proteins that cause nervous tissue death.

Spongiform Encephalopathy

The condition resulting from prion infection where the brain develops holes and resembles a sponge.

Phagocytes

Cells like macrophages that serve as a first line of defense by engulfing and destroying viral particles in a phagolysosome.

Cytotoxic T Lymphocytes

Killer T cells that recognize viral antigens presented on MHC class one and release perforin to destroy infected cells.

Interferon

A protein released by infected cells to alert neighboring cells to produce antiviral proteins.

Nucleoside Analogs

Antiviral drugs that mimic nucleotides to 'fake out' polymerase enzymes and stop viral $DNA$ replication.

Acyclovir

A nucleoside analog used to treat herpes viruses, including chickenpox and shingles.

Neuraminidase Inhibitors

Medications like Oseltamivir (Tamiflu) that block the release of influenza viruses from host cells.

Fusion Inhibitors

Antiviral medications, such as Selzentry, that prevent viruses like HIV from attaching to and entering healthy $CD4$ T lymphocytes.

Protease Inhibitors

Drugs that block viral protease enzymes (molecular scissors) from cutting large protein chains into functional individual proteins.