Virology Overview Quiz

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Questions and Answers

What happens during the assembly phase of phage replication?

Genome is packed into capsid and phage structures are assembled (correct)

Phage injects genetic material into the cell

Host cell factors are commandeered to replicate viral genes

Bacterial cell lyses to release new phages

How do enveloped viruses typically release from a host cell?

By utilizing endocytosis for exit

By budding off from the host cell (correct)

By rupturing the host cell membrane

By forming a provirus within the host

Which statement describes persistent infections?

Viruses avoid immune system clearance through various strategies (correct)

Viruses replicate rapidly and lead to cell lysis

Viruses cause immediate symptoms and are quickly eliminated

Viruses integrate into the bacterial genome without symptoms

What is the role of a provirus in a viral infection like HIV?

To integrate the viral genome into the host cell's DNA (C) Signup and view all the answers

Which method is commonly used to detect viruses?

Searching for viral genetic material or proteins in samples (D) Signup and view all the answers

What is the primary purpose of antibodies in agglutination tests?

To bind viral antigens (C) Signup and view all the answers

What limitation is associated with enzyme-linked immunosorbent assays (ELISA)?

Time needed for detectable antibody levels (D) Signup and view all the answers

Which method is NOT typically used to detect viral nucleic acids?

Enzyme-linked immunosorbent assays (ELISA) (C) Signup and view all the answers

What do prions cause in host organisms?

Transmissible spongiform encephalopathies (TSEs) (B) Signup and view all the answers

What is the main function of nucleoside analogs in antiviral treatment?

Block nucleic acid replication (A) Signup and view all the answers

What characterizes viruses as obligate intracellular pathogens?

They require a host cell to replicate. (C) Signup and view all the answers

What is the primary function of a viral capsid?

To package and protect the viral genome. (D) Signup and view all the answers

How do enveloped viruses acquire their lipid-based envelope?

They obtain it by budding off the host cell. (B) Signup and view all the answers

What type of viral genome requires transcription before translation into proteins?

Double-stranded RNA. (A), Single-stranded negative RNA. (D) Signup and view all the answers

What is the significance of attenuated strains in vaccines?

They are genetically altered to limit infectivity. (C) Signup and view all the answers

Which term describes the specific type of cells or tissues that a virus can infect?

Tropism. (A) Signup and view all the answers

What type of viruses exhibit a faster rate of genomic change compared to living infectious agents?

RNA viruses. (A) Signup and view all the answers

Which structure aids viruses in attaching and entering host cells?

Viral spikes (peplomers). (D) Signup and view all the answers

Which of the following statements is true about naked viruses?

They lack an envelope and usually lyse the host cell upon release. (C) Signup and view all the answers

Which of the following can be seen as a beneficial mutation for a virus?

Ability to escape host immune detection. (C) Signup and view all the answers

Study Notes

Virology

The study of viruses.

Viruses

Submicroscopic, infectious agents.
Acellular and obligate intracellular pathogens.
Extremely small (20–400 nm).
Infect a wide range of organisms including bacteria, animals, and plants.

Virion

A single, infectious virus particle.
Contains genetic material (DNA or RNA) enclosed within a protective protein capsid.

Capsid

Protein shell that packages and protects the viral genome.
Made up of capsomere subunits.
Accounts for the majority of a virion's mass.

Enveloped Viruses

Have a lipid-based envelope surrounding the capsid.
Acquire the envelope from the host cell membrane during budding.

Naked Viruses

Lack an envelope.
Released from the host cell by lysis (bursting).

Viral Spikes (Peplomers)

Glycoprotein extensions protruding from the viral capsid or envelope.
Facilitate attachment and entry into host cells by binding to specific receptors.

Viral Genomes

Can be RNA or DNA, single or double-stranded, segmented or linear, and circular or linear.

RNA Viruses: mRNA Production

Single-stranded positive RNA (ssRNA +): The viral genome acts as mRNA, directly translated by host ribosomes.
Single-stranded negative RNA (ssRNA -): The viral genome is complementary to mRNA. It is transcribed into mRNA by RNA-dependent RNA polymerases (RdRPs).

Single-stranded Retroviruses

RNA genome is converted to DNA by reverse transcriptase.
DNA is often integrated into the host cell's DNA.
Integrated DNA is transcribed into mRNA.

Double-stranded RNA Genome (dsRNA)

Transcribed into mRNA by RNA-dependent RNA polymerases.

Viral Genomic Change

Viruses exhibit rapid genomic change due to:
- Short replication time.
- High virion production rates.
- Higher mutation rates in RNA genomes compared to DNA.
  - DNA polymerases have proofreading capabilities.
  - RNA polymerases lack proofreading abilities.

Attenuated Strains

Genetic changes that reduce a virus's infectivity can lead to attenuated strains used in vaccines.

Beneficial Viral Mutations

Mutations can enhance viral survival by:
- Evading host immune system detection.
- Broadening host range.
- Expanding tropism.
- Increasing infectivity.

Host Range

The collection of species a virus can infect.

Tropism

Tissue or cell specificity of a virus.
Determined by viral surface factors and host cell receptors.

Broad Tropism

Viruses that infect a wide range of host cells or tissues.

Narrow Tropism

Viruses that infect only one type of host cell or tissue.

Viral Replication

Viruses hijack host cell machinery to multiply.

Generalized Bacteriophage Replication

Attachment (adsorption): Phage binds to bacterial cell.
Penetration (entry): Phage injects genetic material into the cell.
Replication (synthesis): Phage utilizes host cell factors to transcribe and translate viral genes.
Assembly (maturation): Genome is packaged into the capsid, and phage structures are assembled.
Release: Bacterial cell lyses, releasing newly formed phages.

Generalized Animal Virus Replication (Penetration)

Enveloped viruses: Enter by endocytosis or membrane fusion.
Naked viruses: Enter by endocytosis.

Generalized Animal Virus Replication (Release)

Enveloped viruses: Released by budding.
Naked viruses: Released by host cell lysis.

Acute Infections

Viruses infect a host cell, leading to immediate new virion production.

Persistent Infections

Viruses employ strategies to evade the immune system, leading to chronic or latent infections.

Provirus

Some viruses (e.g., HIV) integrate their genome into the host cell DNA, forming a provirus.

Oncogenic Viruses (Oncoviruses)

Viruses capable of causing cancer.
Responsible for approximately 10–15% of cancers.

Virus Detection Techniques

Standard light microscopy is not suitable for virus detection.
Molecular methods are commonly used:
- Detection of viral genetic material.
- Identification of viral proteins.
- Detection of antibodies against viral proteins in patients.

Viral Protein Detection

Utilizes purified antibodies to bind viral antigens.

Agglutination Tests

Purified antibodies linked to latex beads are mixed with a sample.
Antibodies bind viral antigens, causing the beads to agglutinate (clump together).

Enzyme-linked Immunosorbent Assays (ELISA)

Adapted to detect either antigens or antibodies in a sample.
Target binds to a surface, and a color change indicates binding.

Limitations of ELISA and Agglutination Assays

Detectable antibody levels can take time to develop (seroconversion window).

Viral Nucleic Acid Detection

A growing trend in diagnostics.
Very specific segments of viral nucleic acid are detected using:
- Fluorescent-labeled probes.
- Sequencing.
- Polymerase chain reaction (PCR).

Antiviral Drugs

Primarily limit infections, rather than cure them.

Vaccines

Train the immune system to recognize and fight viruses.
Effective means of limiting infection.

Nucleoside Analogs

Block nucleic acid replication.

Interferons

Naturally occurring substances released by cells in response to viral infections.

Oseltamivir (Tamiflu) and Zanamivir (Relenza)

Prevent influenza A and B virions from budding from the host cell surface.

Prions

Infectious proteins lacking genetic material.
Do not replicate.
Misfolded prion proteins trigger aggregation of specific host proteins.
Cause transmissible spongiform encephalopathies (TSEs).

Spongiform Encephalopathies

Can be inherited or acquired.

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Description

Test your knowledge on the fundamentals of virology, including the structure and types of viruses. This quiz covers concepts such as virions, capsids, and viral genomes, as well as the differences between enveloped and naked viruses. Challenge yourself and learn more about these fascinating infectious agents.