Ch 7 Introduction to Viruses: Structure, Classification, and Life Cycle Study Guide | Quizlet

Why are viruses classified as obligate intracellular parasites?

They lack cellular structures and metabolic machinery, requiring a host cell to replicate and propagate.

What is the ultramicroscopic size range of viruses?

Viruses range in size from $20\,nm$ to $1,500\,nm$.

What is the diameter measurement of parvoviruses reported in the notes?

Parvoviruses measure about $0.02\,\mu m$ in diameter.

How do the genome sizes of Hepatitis B and pandoraviruses compare?

Hepatitis B has only $4$ genes, whereas pandoraviruses have over $2,500$ genes.

What are capsomeres (capsomers)?

Protein subunits that self-assemble to form the protective viral capsid.

What is a virion?

The complete virus particle capable of infecting a host.

What geometric features characterize an icosahedral capsid?

It is a three-dimensional structure consisting of $20$ triangular faces and $12$ vertices.

What estimated percentage of the human genome consists of remnants from ancient viral infections?

$40\%$ to $80\%$ of the human genome.

What are complex capsids, and what is a primary model studied for this structure?

Asymmetrical capsids composed of multiple types of proteins found in bacteriophages, such as T-even bacteriophages T-2 and T-4.

What criteria are used in the Baltimore Classification System to divide viruses into seven groups?

The type of nucleic acid (DNA or RNA) and its replication strategy or method.

What suffixes are used in formal classification for viral orders, families, and genera?

Orders use the suffix -virales, families use -viridae, and genera use -virus.

How do Hepatitis B, poliovirus, and rabies virus differ in their host range?

Hepatitis B has a restricted host range, poliovirus has a moderately restrictive host range, and rabies virus has a broad host range.

In which cellular compartments do animal RNA viruses versus DNA viruses typically replicate?

RNA viruses typically replicate in the cytoplasm, while DNA viruses replicate in the nucleus.

How are mature enveloped viruses released from host cells without immediately destroying them?

By budding or exocytosis, which allows for gradual shedding while the host cell remains viable.

What are cytopathic effects (CPEs), and what are two common indicators of them?

Virus-induced damage altering the microscopic appearance of host cells; inclusion bodies and syncytia formation are common indicators.

What is a provirus?

Viral DNA integrated into the host cell genome, establishing a chronic latent state with periodic reactivation.

What percentage of human cancers are linked to oncogenic viruses?

Approximately $13\%$ of human cancers.

In what year were bacteriophages discovered?

Bacteriophages were discovered in $1915$.

What is the key functional difference between the lytic cycle and the lysogenic cycle?

The lytic cycle culminates in host cell lysis to release new virions, while the lysogenic cycle integrates viral DNA into the host genome as a prophage without immediate lysis.

Which bacteriophage is identified as an example that undergoes the lysogenic cycle?

The lambda phage.

What naturally occurring protein shows promise in treating certain viral infections?

Interferon (IFN).

What are prions and what type of diseases do they cause?

Infectious agents composed solely of protein that lack nucleic acids; they cause spongiform encephalopathies.

What human disease and two animal diseases are caused by prions according to the notes?

Creutzfeldt-Jakob Disease (CJD) in humans, scrapie in sheep, and bovine spongiform encephalopathy (mad cow disease) in cattle.

What are viroids and what types of organisms do they infect?

Small, circular RNA molecules lacking a protein coat that infect plants, such as tomatoes and potatoes.

What is a satellite virus, and what specific example is mentioned?

A virus that requires co-infection with a helper virus for replication, such as adeno-associated virus (AAV).