CLSC 2429 Unit 2 Chapter 5: Viruses and Prions

What are the four main parts of a virus?

Nucleic acid (DNA/RNA) in the core, covered by a capsid (protein shell), sometimes an envelope, and spikes for attachment.

List the five steps viruses use to invade cells.

1. Adsorption (spikes bind).

2. Penetration & Uncoating (entry, nucleic acid released).

3. Synthesis (parts made by host machinery).

4. Assembly (parts combine).

5. Release (by budding or lysis).

Why are antivirals hard to make, and what must they target?

Hard because viruses use host cells. They must target a specific step of the viral life cycle.

What's the difference between an antibiotic and an antiviral?

Antibiotics treat bacterial infections. Antivirals treat viral infections by inhibiting replication. They are not interchangeable.

Define persistent infection and give two types.

Infections lasting weeks to a lifetime.

Provirus (DNA incorporates, Measles) or Chronic Latent State (inactive, HSV) .

What are oncogenic viruses (oncoviruses)?

Viruses that cause cancer. Examples: Hepatitis B, Papillomavirus, Epstein-Barr virus.

Define bacteriophage.

A virus that infects bacteria.

Contrast the lytic and lysogenic cycles.

Lytic: Replication leads to bacterial cell lysis (death).

Lysogenic: Viral DNA (prophage) integrates into host chromosome, remaining dormant.

Why are temperate phages important in healthcare?

Lysogeny allows bacteria to gain toxins or enzymes (prophage provides adaptive genes) making them more harmful (e.g., Diphtheria).

Differentiate CJD, vCJD, and BSE.

All are fatal spongiform diseases caused by prions. 

CJD is spontaneous/genetic.

BSE ("Mad Cow Disease") is in cattle.

vCJD is the human form from eating contaminated beef.

How are viruses cultured in a lab?

They require live cells using: live animals, bird embryos, or cell/tissue culture . Damage observed in culture is called cytopathic effects.

Where do DNA viruses typically replicate their nucleic acid (NA) in the host cell?

In the host cell nucleus.

Where do RNA viruses typically replicate their nucleic acid (NA) in the host cell?

In the host cell cytoplasm

The formation of a multinucleate cell when adjacent host cells fuse together is called a syncytium, which is caused by which virus?

Respiratory Syncytial Virus (RSV).

What is the term for the accumulation of structures (like Negri bodies) in the host cell cytoplasm or nucleus, often used to diagnose viral infections?

Inclusion bodies.

Which cytopathic effect is characterized by host cells being killed completely, shrinking, detaching from the surface, and lysing?

Poliovirus.

The central core of a virus particle contains the nucleic acid (DNA or RNA) and may also contain what other components?

Matrix proteins and Enzymes.

Name the two common ways a virus can achieve Penetration and Uncoating into a host cell.

1. Host's lysosome brings the virus in through endocytosis (engulfment). 2. Direct fusion of the virus and host cell membrane

How are nonenveloped and complex viruses released from the host cell?

They are released when the host cell lyses or ruptures.

How are enveloped viruses released from the host cell?

They are liberated by budding from the host cell's membranes, picking up the envelope as they exit.

What are Prions?

Misfolded protein fibrils in brain tissue that cause fatal neurodegenerative diseases.