MicroBio Chapter 5 Study questions

• What are the main components of a virus's structure?

External coating, core containing DNA or RNA, sometimes enzymes.

• What is a capsid, and what is it made of?

Protein shell surrounding the viral nucleic acid.

• What are the two structural types of capsids? Describe each.

• Helical: Rod-shaped capsomeres form hollow cylinders into a continuous helix.

• Icosahedral: 3D, 20-sided figure with 12 evenly spaced corners.

• What is a nucleocapsid?

Capsid plus nucleic acid.

• What is the difference between naked and enveloped viruses?

Naked viruses have only nucleocapsid; enveloped viruses have a phospholipid bilayer membrane from the host surrounding the capsid.

• Where do viral envelopes originate from?

Modified piece of the host’s cell membrane.

• What are viral spikes, and what is their role?

Proteins on the virus surface that allow docking to host cells.

• What is a virion?

A fully formed virus able to infect a host cell.

• What type of nucleic acids can viruses contain?

DNA or RNA.

• How does the size of a viral genome compare to that of a cell?

Viral genome is smaller than cellular genomes.

• What types of nucleic acid structures can viruses have (e.g., linear, circular)?

Single or double-stranded, linear, circular, or segmented.

Why do some viruses carry their own enzymes?

Some viruses carry enzymes for specific operations inside host cells.

• What are the general phases of the animal virus replication cycle?

Adsorption, penetration and uncoating, synthesis, assembly, release.

• What is adsorption, and how does it determine host range?

Virus attaches specifically to host cell receptors; determines host range.

• What happens if a host cell lacks the right receptor for a virus?

The virus cannot adsorb or invade; the cell is resistant.

• What are two methods of penetration used by animal viruses?

Endocytosis (whole virus engulfed), direct fusion (envelope merges with membrane).

• What is uncoating, and how does it occur?

Enzymes dissolve capsid/envelope, releasing viral nucleic acid into cytoplasm.

• Where are DNA viruses typically replicated and assembled?

Nucleus.

• Where are RNA viruses typically replicated and assembled?

Cytoplasm.

• Describe how enveloped viruses are released from the host cell.

Budding—virus pushes through host membrane, taking a piece of it as envelope.

How does lytic release differ from budding?

Host cell bursts to release viruses; different from budding which is gradual.

• What are cytopathic effects (CPEs)?

Virus-induced changes in cell appearance or function.

• Give three examples of CPEs.

• Changes in shape/size, inclusion bodies, syncytia (fused cells).

• What is a persistent infection?

Virus remains in host cell without immediate lysis.

• How long can persistent viruses remain in the host?

Weeks to lifetime of host.

• What is a provirus?

Viral DNA integrated into host DNA.

• Are new viruses produced during the provirus stage?

No.

• What is a chronic latent state? Give two examples of viruses that enter this state.

Virus periodically activates; examples include oral/genital herpes and chickenpox/shingles.

• How can viruses cause cancer?

By carrying oncogenes or inserting near host oncogenes.

• What are oncoviruses? List three examples.

Papillomaviruses, herpes virus, hepatitis B virus.

What are three features of transformed cells?

Increased growth rate, altered surface molecules, ability to divide indefinitely.

• What is a bacteriophage?

• Virus that infects bacteria.

• What bacterium is infected by the T-even phage?

E. coli

• What is lysogeny?

Viral DNA integrates into bacterial genome and replicates silently.

• What is a temperate phage?

Phage capable of lysogeny.

• What steps of replication are skipped during lysogeny?

Replication and release are skipped during lysogenic phase.

• What is a prophage?

Dormant bacteriophage DNA integrated into bacterial genome.

• How is the prophage replicated?

Copied during normal bacterial cell division.

What is induction?

Prophage activates, resumes viral replication, leading to lytic release.

• What is lysogenic conversion?

Bacteria acquire new traits from phage genes.

• How can phage genes contribute to human disease?

They can cause toxin/enzyme production causing human pathology.

Name three bacteria that become more pathogenic due to phage infection.

Corynebacterium diphtheriae, Clostridium botulinum, Escherichia coli.

• What are prions?

Infectious protein-only agents.

• What is unusual about how prions cause infection?

Exact mode unknown; no nucleic acid involved.

• What is the term for the group of diseases caused by prions?

Transmissible spongiform encephalopathies (TSEs).

• What does affected brain tissue look like under a microscope?

Sponge-like appearance under microscope.

• How are most prion diseases transmitted?

Contact with infected tissue, fluids, or medical instruments; not airborne or casual contact

• Are prion diseases fast-acting or slow-developing?

Long period before symptoms appear.

• Are prion diseases curable?

No cure; diseases are fatal and progressive.

Name three prion-associated diseases.

Creutzfeldt-Jakob Disease, Bovine Spongiform Encephalopathy, Kuru.

• Who is responsible for officially classifying viruses?

International Committee on the Taxonomy of Viruses (ICTV).

• What four main criteria are used in virus classification today?

Hosts/diseases caused, structure, chemical composition, genetic similarities.

• What naming system do clinicians often use?

Common names are used.

• What is the genome of a virus?

Total genetic information of a virus.

How does virus structure relate to its ability to infect specific hosts?

Spikes and envelopes help virus dock and enter specific host cells.