Chapter 13: Characterizing and Classifying Viruses, Viroids, and Prions

Vocabulary flashcards covering viral structure, classification, replication cycles, plant viruses, viroids, and prions based on Chapter 13 lecture slides.

Virion

An extracellular state of a virus consisting of a protein coat (capsid) surrounding nucleic acid, and sometimes a phospholipid envelope.

Nucleocapsid

The combination of a virus's nucleic acid and its surrounding protein coat (capsid).

Capsid

The protein coat that surrounds and protects viral nucleic acid, composed of individual protein subunits called capsomeres.

Capsomeres

The protein subunits that assemble to form the protective capsid of a virus.

Viral Envelope

An outer membranous layer surrounding the capsid of some viruses, composed of a phospholipid bilayer and proteins acquired from host cell membranes during viral replication or release.

Bacteriophages

Viruses that specifically infect bacterial cells; also called phages.

Lytic Cycle

A viral replication cycle in bacteriophages that leads directly to host cell lysis and cell death.

Lysogenic Cycle

A viral replication cycle in which a bacteriophage remains latent within the host bacterial cell, integrating its genome into the host cell DNA.

Prophage

Inactive bacteriophage DNA that has been integrated into the circular chromosome of a host bacterium during lysogeny.

Phage Conversion

A change in host phenotype induced by a prophage, such as conferring toxin-producing abilities to the bacterial cell.

Specialized Transduction

A process in which specific host bacterial genes adjacent to an integrated prophage are excised along with phage DNA and transferred to a new host cell.

Positive-Sense (+RNA)

Single-stranded viral RNA that is equivalent to mRNA and can be directly translated into proteins by host ribosomes.

Negative-Sense (-RNA)

Single-stranded viral RNA that is complementary to mRNA and cannot be directly translated; it must first be transcribed by RNA-dependent RNA transcriptase.

Reverse Transcriptase

A viral enzyme used by retroviruses to synthesize a double-stranded DNA copy from an RNA genome template.

Provirus

Viral DNA that is permanently integrated into an animal host cell's chromosome.

Latent Viral Infection

A state in which a virus remains present within a host cell for long periods without causing disease or visible symptoms.

Persistent Viral Infection

A viral infection in which disease occurs gradually over a long period of time and is eventually fatal.

Protooncogenes

Normal cellular genes that promote cell growth and division, which can lead to cancer if inappropriately activated.

Plaque

A clear area on an agar plate within a lawn of bacterial growth where bacteriophages have infected and lysed host bacteria.

Plaque-Forming Units (PFU)

A quantitative measurement unit used to calculate the concentration of infective viral particles in a suspension.

Cytopathic Effect (CPE)

Observable structural or degenerative changes in cultured host cells caused by viral infection.

Viroids

Extremely small, circular pieces of infectious single-stranded RNA that lack a protein capsid and cause disease in plants.

Prions

Proteinaceous infectious agents lacking nucleic acid that cause neurodegenerative diseases by altering normal host proteins into misfolded infectious forms.

Cellular PrP (c-PrP)

The normal, functional form of prion protein synthesized by host cells, containing ̑\alpha-helices.

Prion PrP (p-PrP)

The disease-causing, misfolded form of prion protein characterized by $\beta$-pleated sheets that converts normal c-PrP into p-PrP.

Spongiform Encephalopathies

A group of fatal neurological diseases caused by prions, characterized by the development of large vacuoles in brain tissue.