chap 6 micro lecture virus

What is mechanical transmission?

When an arthropod carries a virus on the outside of its body and transmits it to a new host through physical contact.

What is biological transmission?

When an arthropod carries a virus inside its body and transmits it to a new host through biting.

What are zoonoses?

Viruses that can be transmitted from animal hosts to humans, causing disease.

What do viruses consist of?

A nucleic acid (RNA or DNA, never both) surrounded by a protein coat (capsid).

What is inside the capsid of a virus?

The viral genome and enzymes needed to make new virions.

What is a capsid made of?

Protein subunits called capsomeres.

What is a bacteriophage?

A virus that infects bacteria.

What are naked (nonenveloped) viruses?

Viruses made of only nucleic acid and a capsid, without a lipid envelope.

What are enveloped viruses?

Viruses that have a nucleic-acid-packed capsid surrounded by a lipid envelope.

Where does a viral envelope come from?

It is a portion of phospholipid membrane obtained as the virion buds from a host cell.

What are viral spikes?

Protein structures that extend from the capsid (naked viruses) or the envelope (enveloped viruses) to attach and enter host cells.

What are the three main viral capsid shapes?

Helical, polyhedral (icosahedral), and complex.

Describe a polyhedral (icosahedral) capsid.

A three-dimensional, 20-sided structure with 12 vertices, resembling a soccer ball.

What is a complex-shaped virus?

Viruses like T4 bacteriophage or poxviruses, which don’t fit neatly into helical or icosahedral categories.

how is the genome arranged in a complex bacteriophage like T4?

The genome is inside the polyhedral head, connected by a sheath to tail fibers that attach to host cell receptors.

Where do bacteriophages replicate?

Only in the cytoplasm, because prokaryotic cells lack a nucleus and organelles.

Where do most DNA viruses replicate in eukaryotic cells?

Inside the nucleus, except for some large DNA viruses like poxviruses, which replicate in the cytoplasm.

Where do most RNA viruses that infect animal cells replicate?

In the cytoplasm, with a few exceptions.

How many stages are there in viral replication?

Five stages (attachment, entry, synthesis, assembly, release).

What type of bacteriophage can undergo both lytic and lysogenic cycles?

A temperate bacteriophage.

What happens to phage DNA in the lysogenic cycle?

It is incorporated into the host genome, forming a prophage that is passed on to future generations.

What can trigger a prophage to exit the lysogenic cycle and enter the lytic cycle?

Environmental stressors, such as starvation or exposure to toxic chemicals.

How can a prophage affect the phenotype of its bacterial host?

By bringing in extra genes, like toxin genes, which can increase bacterial virulence.

What is the term for a change in bacterial phenotype caused by a prophage?

Lysogenic conversion or phage conversion.

How do animal viruses enter host cells?

Through endocytosis (engulfment) or membrane fusion (viral envelope fuses with host membrane).

How are new virions released in influenza infection?

By budding from the host cell.

What happens after the virus is engulfed?

Viral RNA and proteins are made and assembled into new virions.

Which RNA virus replicates in the nucleus instead of the cytoplasm?

Influenza virus.

How do dsDNA viruses replicate in host cells?

They follow the normal DNA → RNA → protein flow, like cellular organisms.

What happens when a virus has a ssDNA genome?

Host enzymes synthesize a complementary strand to form dsDNA, which then follows DNA → RNA → protein.

What are the three types of RNA viral genomes?

dsRNA, +ssRNA (positive single-strand), and −ssRNA (negative single-strand)

How does +ssRNA function in viral replication?

It acts like cellular mRNA, which can be directly translated into proteins.

How is −ssRNA replicated?

Viral RNA-dependent RNA polymerase (RdRP) converts −ssRNA into +ssRNA, which can then be translated.

How do dsRNA viruses use RdRP?

RdRP uses the negative strand of dsRNA as a template to make +ssRNA, which is then translated by cellular ribosomes.

What is a prion?

A misfolded rogue form of a normal protein (PrPc) found in the cell.

How do prions become infectious?

The rogue prion protein (PrPsc) stimulates normal proteins to misfold, forming plaques.

What are viroids?

Acellular, virus-like particles consisting of a short circular RNA strand capable of self-replication.

What was the first viroid discovered?

Potato spindle tuber viroid (PSTV), which causes potato tuber spindle disease with slower sprouting and deformities.

How do viroids replicate?

They take control of the host cell machinery to replicate their RNA genome.

What are virusoids?

Non–self-replicating ssRNAs that infect plants but require a specific “helper” virus to replicate.

How is virusoid replication different from viroids?

Viroids replicate independently using host machinery, while virusoids need a helper virus for replication.

How can membrane filters be used in viral studies?

They remove cells or viruses from a solution; the pore size determines what is captured and what passes through. Viruses can pass through finer filters that block animal or bacterial cells.

How are human or animal cells cultured for viral studies?

In flasks containing the appropriate host cells to support viral replication.

What happens during the inoculation stage?

Virions attach to host cells.

What happens during the eclipse stage?

The viral genome enters the host, and no new virions are yet detectable.

What happens during the burst stage?

New virions are produced and released from the host cell.

What is the burst size?

The maximum number of virions produced per bacterium.

What is a persistent infection?

An infection where the virus is not completely cleared and remains in certain tissues/organs.

In a latent infection, what happens to the virus?

It stays dormant in host cells and can reactivate later.

What is a retrovirus?

A virus that uses reverse transcriptase to convert its RNA genome into DNA and integrate into the host genome.

Once inside the cell, what enzyme do retroviruses use?

Reverse transcriptase.

What does reverse transcriptase do?

Converts single-stranded RNA into double-stranded DNA.