Applied Microbiology week 8: Acellular Microbes, Viruses and Prions

This set covers the vocabulary and foundational concepts regarding viruses, viroids, satellites, and prions as presented in Lecture 7.

Transcription

The process where DNA is copied into messenger RNA (mRNA).

Translation

The process where mRNA is used to build a protein at the ribosome.

Viruses

Acellular agents composed of nucleic acid (DNA or RNA) enclosed in a protein coat (capsid), sometimes with a lipid envelope.

Viroids

Acellular agents consisting of small, circular RNA molecules only, primarily infecting plants, with no protein coat.

Prions

Acellular agents made up of misfolded proteins only, containing no nucleic acid.

Satellites

Incomplete viral agents that require a helper virus to replicate.

Adolf Mayer

The scientist who in 1876 investigated tobacco mosaic disease and demonstrated it was infectious via filtered plant extracts.

Pierre Roux

Scientist who in 1903 defined viruses as filterable, invisible under light microscopy, and non-culturable on standard media.

Edward Jenner

Scientist who in 1796 developed the first vaccination by using cowpox to provide smallpox protection.

Obligate intracellular parasites

Agents that require living host cells to replicate, such as viruses.

Virion

A complete, infectious virus particle outside a host cell.

Bacteriophage (Phage)

A virus that specifically infects bacteria.

Capsid

The protein coat that surrounds and protects the viral nucleic acid.

Nucleocapsid

The core structure present in all viruses, composed of nucleic acid and the capsid.

Capsomeres

Repeating protein subunits that make up the capsid and determine the shape of the virus.

Protomers

Basic protein subunits that assemble into capsomeres.

Helical Capsids

Protein structures that form a hollow, tube-like shape built from repeating protomers in a spiral arrangement.

Icosahedral Capsids

Spherical-like viral capsids made up of $20$ triangular faces, composed of pentamers (pentons) and hexamers (hexons).

Viral Envelope

An outer, flexible lipid membrane derived from the host cell that surrounds the nucleocapsid of some viruses.

Peplomers (Spikes)

Viral glycoproteins embedded in the envelope involved in attachment, entry, and release from host cells.

$+$ sense RNA ($+$ssRNA)

Viral RNA that acts like mRNA and can be translated directly into protein once inside the host cell.

$-$ sense RNA ($-$ssRNA)

Viral RNA that must be converted to mRNA first before it can be translated.

Tropism

The specificity of a virus for particular host species (host range) or specific cells (tissue tropism).

Uncoating

The step in the viral life cycle where the capsid is removed or broken down to release viral nucleic acid.

Early proteins

Viral proteins produced during biosynthesis that modify or take control of the host cell for replication.

Budding

A release mechanism for enveloped viruses where the virus exits through the host membrane, which then becomes the viral envelope.

Retroviruses

Viruses that use reverse transcriptase to convert their ssRNA genome into dsDNA, reversing the usual flow of genetic information.

Provirus

Viral DNA of a retrovirus that has integrated into the host cell's genome.

Lytic Cycle

A reproductive strategy where the virus immediately replicates and induces host cell lysis to release new virions.

Lysogenic Cycle

A reproductive option for temperate phages where the viral DNA integrates into the host genome as a prophage.

Induction

The process of activating a prophage to leave the lysogenic cycle and enter the lytic cycle, often triggered by stress.

Cytopathic Effects (CPEs)

Visible structural changes in eukaryotic cells caused by viral infection, such as cell rounding or detachment.

Syncytium formation

A cytopathic effect where multiple infected host cells fuse into a single large cell with multiple nuclei.

Transformation

An oncogenic infection where a virus alters the host cell, resulting in a malignant or cancerous state.

Plaques

Clear zones in a lawn of host cells on agar indicating areas of host cell destruction by viruses.

$$PFU/mL$$

Plaque Forming Units per mL; calculated as the number of plaques divided by the dilution factor.

$$ID_{50}$$

The amount of virus required to infect $50\%$ of exposed host cells or organisms.

$$LD_{50}$$

The amount of virus required to kill $50\%$ of exposed host organisms; a measure of virulence.

Transmissible Spongiform Encephalopathies (TSEs)

Fatal neurodegenerative diseases caused by prions characterized by hole-like changes in brain tissue.

$$PrP^C$$

The normal, properly folded cellular form of the prion protein found in neurons.

$$PrP^{Sc}$$

The misfolded, infectious form of the prion protein that is resistant to proteases.