Chapter 1-7 Virology and Microbial Genetics Flashcards

Flashcards covering acellular pathogens, virus structure and replication, RNA & DNA virus biology, bacteriophages, retroviruses, antiviral strategies, viroids/virusoids/prions, and horizontal gene transfer.

What defines acellular pathogens and why are they not considered cells?

Acellular pathogens lack a plasma membrane and ribosomes, cannot express their own genetic information or run metabolism, and must infect a host cell to replicate.

List examples of acellular pathogens mentioned in the notes.

Viruses, viroids (plant pathogens), virusoids, and prions (infectious proteins). The hepatitis D virus is noted as a virusoid that requires hepatitis B for pathology.

What is a virion?

A fully assembled infectious viral particle consisting of nucleic acid enclosed in a protein capsid, sometimes with an envelope.

What is the role of a viral envelope and what is it made of?

An outer lipid envelope surrounding the capsid, containing spikes that help determine host range and entry; envelopes are derived from host membranes but include viral proteins.

How do bacteriophages differ from animal viruses in structure and host range?

Bacteriophages have complex, non-enveloped structures with heads and tails designed to infect bacteria; animal viruses vary widely in morphology and infect animal cells.

Name the five general steps of viral replication common to many viruses.

Attachment, penetration, biosynthesis, maturation, and release.

What does host range mean for a virus?

The species and/or cell types that a virus can infect, determined by receptor compatibility and other host–virus interactions.

Identify three common virus morphologies.

Helical, polyhedral (icosahedral), and enveloped (plus the complex form seen in bacteriophages).

What are lytic and lysogenic cycles in bacteriophages?

Lytic cycle: phage replicates and lyses the host to release virions; Lysogenic cycle: phage DNA integrates into the host genome as a prophage and can later induce to enter the lytic cycle.

What is a prophage?

Phage DNA integrated into the bacterial chromosome during lysogeny.

Define phage conversion and specialized transduction.

Phage conversion: bacterial phenotype changes due to phage gene acquisition; specialized transduction: during excision, phage can carry adjacent bacterial genes to new hosts.

What makes retroviruses distinct and what enzymes do they carry?

Retroviruses use reverse transcriptase to convert RNA into DNA and integrase to insert viral DNA into the host genome.

What is a provirus?

Viral DNA that has been integrated into the host genome and can be transcribed/translated to produce viral components.

How do animal enveloped and non-enveloped viruses typically enter host cells?

Enveloped viruses often enter via fusion with the host membrane or endocytosis; non-enveloped viruses usually enter via endocytosis alone.

What are H spikes and N spikes in influenza, and what do they do?

H (hemagglutinin) spikes attach to host cells; N (neuraminidase) spikes help release virions by cleaving sialic acid.

Why are influenza vaccines updated annually?

Because flu viruses mutate rapidly, especially in surface proteins like H and N, altering antigenicity and reducing vaccine effectiveness over time.

Give examples of antiviral drugs and their targets as mentioned in the notes.

Tamiflu (oseltamivir) inhibits neuraminidase; zidovudine (AZT) targets reverse transcriptase; remdesivir inhibits viral RNA polymerase; other drugs target protease and integrase.

What are viroids and virusoids?

Viroids are small circular RNAs that infect plants and lack a capsid; virusoids are single-stranded RNAs that require a helper virus to replicate.

What are prions and how do they propagate?

Infectious misfolded proteins without nucleic acids; they induce misfolding of normal proteins, spreading disease through a chain reaction.

What is the major property of prions regarding heat resistance and transmission?

Prions are extremely heat resistant and can be transmissible or inheritable, making them hard to deactivate and disinfect.

What is horizontal gene transfer and how does it differ from vertical transfer?

Horizontal gene transfer is gene exchange between organisms not via reproduction (conjugation, transformation, transduction); vertical transfer is parent-to-offspring transmission.

Describe bacterial conjugation and the role of the F plasmid.

Conjugation transfers plasmids through direct contact via a sex pilus in Gram-negative bacteria; donor is F+, recipient is F−; rolling circle replication transfers a single strand of DNA.

How does Gram-positive conjugation differ from Gram-negative?

Gram-positive bacteria lack sex pili and form a mating bridge for DNA transfer through close cell contact; Gram-negative use sex pili.

Why is plasmid transfer clinically important?

Plasmids can carry antibiotic resistance genes and virulence factors, spreading MRSA and vancomycin resistance among bacteria.

What is transformation in horizontal gene transfer?

Uptake of naked DNA from the environment by a recipient cell, which may recombine into the chromosome and confer new traits.

What is transduction in horizontal gene transfer?

Gene transfer mediated by a virus (typically a bacteriophage) acting as a vector, sometimes transferring bacterial genes to another bacterium.

How do positive-sense and negative-sense RNA viruses differ in protein synthesis requirements?

Positive-sense RNA acts like mRNA and can be translated directly; negative-sense RNA must be copied to a positive-sense mRNA before translation.

What is the replication process for negative-sense RNA viruses?

They must first synthesize a positive-sense RNA copy to serve as mRNA and template to make new negative-sense genomes.

How do double-stranded RNA viruses replicate?

They undergo semi-conservative replication of each strand to form new double-stranded RNA genomes.

What is the basic difference in the nuclear vs cytoplasmic replication of DNA vs RNA viruses?

DNA viruses typically replicate in the nucleus and use host transcription/translation machinery; RNA viruses often replicate in the cytoplasm and may require viral enzymes.

Name the major DNA virus families listed and a disease they’re associated with.

Adenoviridae (acute respiratory diseases), Poxviridae (smallpox, cowpox), Herpesviridae (cold sores, chickenpox, mononucleosis, shingles), Papovaviridae (papillomaviruses and polyomaviruses), Hepadnaviridae (hepatitis B).

How have adenoviruses been used in medicine?

Adenoviruses can be engineered for gene therapy to deliver therapeutic genes to human cells.

What is a Pandora virus and why is it notable?

A giant virus described as enormous for a virus, about the size of a bacterium (~1 μm in width) with a large genome.

How are vaccines for influenza often produced today beyond eggs, and why was this shift pursued?

In addition to eggs, cell culture methods (e.g., canine kidney cells) are used to grow viruses to reduce mutations seen with egg-based methods and improve vaccine accuracy.