Virus Structure, Replication Cycles, and Disease Mechanisms in Virology

Virus

A tiny nonliving infectious agent.

Virology

The study of viruses.

Can viruses reproduce by themselves?

No. They need host cells to replicate.

Capsid

The outer protein shell of a virus.

Two common capsid shapes

Helical and icosahedral.

Viral envelope

A lipid-based layer surrounding the capsid of some viruses.

Naked virus

A virus that does not have a viral envelope.

Spikes

Glycoprotein extensions used for host cell recognition.

Why are viral genomes small?

Viruses lack their own metabolism and organelles, so they have little to code for.

What genetic material can viruses have?

DNA or RNA.

How are viruses commonly classified?

Genome type, genome architecture, capsid type, and envelope presence.

Genome type

Whether a virus uses DNA or RNA.

Genome architecture

The specific way a virus processes its DNA or RNA.

What must a virus ultimately produce to make proteins?

mRNA.

Retrovirus

An RNA virus that uses reverse transcription.

Reverse transcription

The process of making DNA from RNA.

Lytic cycle

A viral replication pathway that produces viruses and lyses the host cell.

Lytic cycle step 1: Attachment

The virus binds to the host cell.

Lytic cycle step 2: Penetration

The virus introduces its genome into the host cell.

Lytic cycle step 3: Replication

The host cell reads and replicates viral genes.

Lytic cycle step 4: Assembly

New viral parts are constructed and put together.

Lytic cycle step 5: Release

The host cell lyses and new viruses are released.

Lysis

The breaking open of a cell.

Lysogenic replication

A pathway where viral DNA becomes part of the host genome.

Prophage

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

What happens to a prophage when the host cell divides?

It is copied along with the host DNA.

Can a prophage later enter the lytic cycle?

Yes, under certain conditions.

Acute viral infection

Virus replicates and is cleared quickly by the immune system.

Examples of acute viral infections

Colds and influenza.

Chronic persistent infection

Virus slowly replicates over a long period.

Example of a chronic persistent infection

HIV.

Latent persistent infection

Virus has periods of dormancy followed by flare-ups.

Example of a latent persistent infection

Herpes virus.

What can antiviral drugs block early in infection?

Attachment, penetration, or uncoating.

Postexposure prophylaxis

Treatment after exposure that helps prevent or reduce infection.

What can antiviral drugs block later in infection?

Replication, assembly, or release.

Nucleoside analogs

Drugs that substitute for normal nucleosides and disrupt viral replication.

Reverse transcriptase inhibitor

A drug that prevents reverse transcriptase from functioning.

Prion

A misfolded protein that acts as an infectious agent.

Why are prions harmful?

Their abnormal shape makes them stick together and form clumps.

What disease type can prions cause?

Spongiform encephalopathies.

What do spongiform encephalopathies damage?

Brain tissue.

Why are prions difficult to destroy?

They require extreme heat, strong chemicals, or specialized autoclaving.