What are Viruses

What are viruses?

• Non-reproducing

• Non-metabolizing

• Obligate intracellular parasites

• Only function inside a host cell

What does "obligate intracellular parasite" mean?

A virus must be inside a living host cell to reproduce.

What is a virion?

A complete virus particle outside a host cell.

What are the three virus designs?

• Naked (unenveloped)

• Enveloped

• Bacteriophages (infect bacteria)

Which viruses infect eukaryotic cells?

• Naked viruses

• Enveloped viruses

Which viruses infect prokaryotic cells?

Bacteriophages (phages)

What are bacteriophages?

Viruses that infect bacteria.

Why is the name "bacteria eaters" not accurate for bacteriophages?

They infect bacteria; they don't actually "eat" them.

What are the two standard parts found in all viruses?

1. Genetic material (genome)

2. Protein capsid

What are the four possible viral genomes?

• Single-stranded DNA (ssDNA)

• Single-stranded RNA (ssRNA)

• Double-stranded DNA (dsDNA)

• Double-stranded RNA (dsRNA)

Which viral genomes are never the genomes of living organisms?

• Single-stranded DNA

• Single-stranded RNA

• Double-stranded RNA

What is the capsid?

The protein shell that protects the viral genome.

What is the capsid made of?

Capsomeres (protein subunits)

What is the most common capsid shape?

Icosahedron (20 sides)

What is a nucleocapsid?

Genome + Capsid

What do naked (unenveloped) viruses have?

Only a nucleocapsid (genome + capsid)

No envelope.

What is the difference between naked and enveloped viruses?

• Naked viruses: Nucleocapsid only

• Enveloped viruses: Nucleocapsid + envelope

Viruses are considered what type of parasites?

Obligate intracellular parasites.

A virus outside a host cell is called what?

Virion.

Genome + capsid = ?

Nucleocapsid.

Naked viruses have what?

Only a nucleocapsid.

Capsids are made of what?

Capsomeres.

Which virus infects bacteria?

Bacteriophage.

Which viruses have an envelope?

Enveloped viruses.

What does the envelope cover?

The nucleocapsid.

What is the envelope made of?

A phospholipid bilayer taken from the last host cell.

Where does the viral envelope come from?

The host cell's plasma membrane.

Are enveloped viruses more or less resistant outside the body?

Less resistant (more vulnerable).

What damages enveloped viruses outside the body?

• Drying (desiccation)

• Chemicals

• Detergents/soap

Why is the envelope beneficial inside the body?

It masks the viral surface, helping the virus avoid detection by the immune system.

What are glycoprotein spikes also called?

Peplomers

Where are peplomers located?

They stick out of the viral envelope.

What is the function of glycoprotein spikes (peplomers)?

They help the virus attach to host cells.

What are matrix proteins also called?

Tegument proteins

What is the function of matrix (tegument) proteins?

They stabilize the viral envelope.

What do matrix (tegument) proteins help extend?

The virus's viability in warm, moist environments.

Do all viruses have an envelope?

No.

Do all viruses have matrix (tegument) proteins?

No.

The envelope is made from what?

A phospholipid bilayer from the last host cell.

Outside the body, enveloped viruses are more vulnerable to what?

Drying and chemicals.

Inside the body, what does the envelope do?

Masks the viral surface from the immune system.

Glycoprotein spikes are also called what?

Peplomers.

Matrix proteins are also called what?

Tegument proteins.

Function of matrix (tegument) proteins?

Stabilize the envelope and extend viability in warm, moist environments