Virology Lecture Notes Review

A comprehensive set of Q&A style flashcards covering key concepts from the virology lecture notes, including virus definition, structure, taxonomy, replication, infection types, identification, and oncogenesis.

Who demonstrated that tobacco mosaic disease (TMD) was transmissible from a diseased plant to a healthy plant in 1886?

Mayer

In 1892, which scientist found that the infectious agent could pass through a filter designed to capture bacteria?

Iwanowski

Define a virus.

A small, filterable infectious agent that contains nucleic acid and a protein coat, multiplies only inside living cells, and can transfer its genome to other cells.

Are viruses living organisms?

No. They are not living outside host cells; they lack metabolism and cannot replicate on their own.

What nucleic acids can viruses contain?

DNA or RNA; can be dsDNA, ssDNA, ssRNA, or dsRNA.

What is a capsid?

The protein coat surrounding the viral nucleic acid, made of capsomeres; may be enveloped.

What is a viral envelope and what is its significance?

A lipid membrane surrounding some viruses; contains spike proteins used for attachment and can aid in identification.

What are the major viral morphologic types?

Helical, Polyhedral, Enveloped, and Complex.

What is a bacteriophage?

A virus that infects bacteria.

What is a plaque and what does plaque-forming units (PFU) measure?

A plaque is a clear zone of lysis on a bacterial lawn; PFU measures infectious virus particles.

Describe the lytic cycle of a bacteriophage.

Attachment/absorption, biosynthesis, maturation/assembly, and release leading to host cell lysis.

Describe the lysogenic cycle.

Phage DNA integrates into the host chromosome as a prophage; the host reproduces normally; prophage can excise later to initiate the lytic cycle.

What is host range?

The range of organisms a virus can infect, usually narrow and determined by attachment proteins and host receptors.

What is tissue tropism?

Infection of specific cell types within a host; even a susceptible host may have select cell/tissue infection.

What is bacteriophage therapy?

Use of phages to kill bacteria in infected tissue; phages can be cleared by the host immune system.

What are the main steps of animal virus replication?

Attachment, penetration, biosynthesis, assembly, and release (with latency possible in some viruses).

What is a provirus?

A viral genome (often dsDNA) integrated into the host cell’s chromosome, typically after reverse transcription in retroviruses.

Which enzyme do retroviruses use to convert RNA to DNA?

Reverse transcriptase.

What is oncogenesis in viruses?

Some viruses carry or induce oncogenes that can transform cells and contribute to tumor formation; about 10–20% of cancers are virus-associated.

What is an oncogene?

A gene whose product promotes cellular transformation or tumor formation; mutations or deregulation can lead to cancer.

How can oncogenic viruses activate cancer in the host cell?

Viral DNA integrates into the host genome; if it carries an oncogene, its expression can drive malignant transformation.

What are the three main classes of viral infections?

Acute infection, latent infection, and persistent infection.

What characterizes an acute viral infection?

Rapid viral replication with immune response; usually cleared by the immune system, though it can be fatal in some cases.

What characterizes a latent viral infection?

The virus remains dormant within cells for long periods and can reactivate later (e.g., herpes simplex).

What characterizes a persistent viral infection?

Long-term, often fatal infection in which the virus accumulates over time and overcomes immune clearance.

What methods are used for viral identification?

Serological testing for antibodies and molecular methods such as PCR and RFLP.

What is PCR and what is it used for in virology?

Polymerase chain reaction; amplifies a specific region of nucleic acid to detect a virus.

What is RFLP and how is it used in viral identification?

Restriction fragment length polymorphism; uses restriction enzymes to cut viral DNA and compare fragment patterns to identify viruses.

What are cytopathic effects and why are they important?

Visible changes in host cells due to viral infection; these effects can be diagnostic and are observed with a microscope.

Give an example of a common cytopathic effect.

Cell rounding/detachment or cell fusion (syncytia) are typical examples.