Basic Concepts in Virology Midterms

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Questions and Answers

What are the key components found in a virion?

Envelope, mitochondria, RNA

Cell wall, cytoplasm, nucleic acid

Nucleus, ribosomes, capsid

Nucleic acid core, protein coat, lipid envelope (correct)

Why are viruses considered obligate intracellular parasites?

They can replicate independently.

They possess cellular structures.

They can produce energy independently.

They require host cells to survive. (correct)

Which of the following statements about viral replication is correct?

Viruses can replicate their genome without host machinery.

The replication process of viruses involves the assembly of individual components. (correct)

Viruses are self-replicating once inside a host cell.

Viruses replicate by binary fission.

Who is credited with the discovery of viruses as filterable organisms?

Dmitri Iwanowski Signup and view all the answers

What is the primary reason viruses lack the ability to produce energy substrates?

They do not possess cellular structures. Signup and view all the answers

What conditions can readily disrupt the latent period of a virus?

Drying and acidic conditions Signup and view all the answers

What are some common modes of transmission for viruses during their latent period?

Respiratory droplets and blood Signup and view all the answers

Which immune responses may be required for protection and control of some viruses?

Antibody and cell-mediated immune response Signup and view all the answers

During which phase of the infectious cycle does viral attachment to the target cell occur?

Attachment (Adsorption) Signup and view all the answers

What initiates the internalization of a virus into a host cell?

Interactions between VAPs and cellular receptors Signup and view all the answers

What does viral tropism refer to?

Preference of virus for certain cell types or species Signup and view all the answers

What is the purpose of the viral assembly stage in the infectious cycle?

To combine structural proteins and genomes into new virus particles Signup and view all the answers

What role do viral attachment proteins (VAPs) play in the virus's infectious cycle?

Binding to receptors on host cells Signup and view all the answers

What process do most nonenveloped viruses use to enter host cells?

Receptor-mediated endocytosis Signup and view all the answers

What is the primary mechanism by which enveloped viruses typically exit a host cell?

Budding from the plasma membrane Signup and view all the answers

During the assembly of viruses, which structure is proposed to be formed initially for capsid viruses?

Procapsid Signup and view all the answers

Where does the genome of most DNA viruses (excluding poxviruses) get delivered after infection?

Nucleus Signup and view all the answers

What is the purpose of the uncoating process in viral infection?

Release of the viral genome Signup and view all the answers

What structure is associated with the formation of multinucleated cells during viral infections?

Syncytia formation Signup and view all the answers

What cellular components are involved in the acquisition of viral envelopes during the budding process?

Nuclear and endoplasmic reticulum membranes Signup and view all the answers

How do viruses that escape the host cell without killing it typically exit?

Exocytosis Signup and view all the answers

Which of the following statements about capsids is correct?

Capsids can be resistant to harsh environmental conditions. Signup and view all the answers

What role can certain viruses play in agriculture?

Serving as natural pesticides. Signup and view all the answers

How do naked viruses release from host cells?

Through lysis of the host cell. Signup and view all the answers

Which type of viral genome structure is NOT found in viruses?

Triple-stranded DNA Signup and view all the answers

What is the primary characteristic of abortive infections?

Viral mutants do not multiply Signup and view all the answers

What is a characteristic of non-symmetric capsids?

They form complex shapes and are associated with certain viruses. Signup and view all the answers

Which type of infection features periods of virus production interspersed with periods of latency?

Recurrent infection Signup and view all the answers

In a chronic infection, what happens during the viral replication process?

Virus synthesis occurs without causing cell death Signup and view all the answers

Which of the following is considered a beneficial use of viruses in medicine?

Acting as gene vectors for gene therapy. Signup and view all the answers

Why are naked viruses considered environmentally stable?

They can withstand drying, acid, and detergents. Signup and view all the answers

Which of the following factors is NOT associated with the innate immune response?

Delayed-type hypersensitivity Signup and view all the answers

What is the primary means by which viruses replicate?

By utilizing cellular components from the host. Signup and view all the answers

What typically occurs during the incubation period of a viral infection?

Asymptomatic amplification of the virus can occur Signup and view all the answers

Which description best fits latent infections?

Low macromolecular activity with no virus synthesis Signup and view all the answers

Transforming infections are associated with which type of viruses?

Oncogenic viruses that can immortalize cells Signup and view all the answers

What type of infection is characterized by viral replication without causing cell lysis?

Persistent infection Signup and view all the answers

Study Notes

Overview of Virology

Virology focuses on the study of viruses, known as the smallest filterable infectious agents.
Dmitri Iwanowski discovered viruses in 1892.

Characteristics of Viruses

Viruses can be living or non-living; classified as obligate intracellular parasites.
They depend on host cells for survival and cannot replicate independently.
Modes of replication involve the assembly of individual components.
Lack energy-generating mechanisms and cannot replicate their genomes without a host.

Viral Structure

Virions consist of three key components:
- Nucleic Acid Core: Contains either DNA or RNA; never both.
- Capsid: A protein coat that protects the nucleic acid, forming the nucleocapsid.
- Envelope: A lipid structure surrounding the virus; present in larger viruses.

Types of Viruses

Naked viruses rely on capsids, which provide structural rigidity and protect the genome from harsh environments.
Environmental stability allows them to endure conditions such as drying and acidic environments.

Viral Origin

Viruses likely originated from host cell DNA or RNA components that gained the ability to exist independently.
Viral genomes may be:
- Double-stranded DNA
- Single-stranded DNA
- Double-stranded RNA
- Single-stranded RNA

Capsid Types

Symmetric Capsids:
- Helical: Rod-like appearance.
- Icosahedral: Spherical shape formed from symmetric subunits.
Nonsymmetric Capsids: Complex forms associated with specific viruses.

Viral Replication Cycle

Six steps of viral replication include:
- Attachment (Adsorption): Viral proteins recognize and bind to host cell receptors, determining host range and viral tropism.
- Penetration (Virus Entry): Viruses enter host cells through multiple mechanisms, influenced by their structure (e.g., receptor-mediated endocytosis for non-enveloped viruses).
- Uncoating: The capsid is removed to release the viral genome into the host cell.
- Incubation Period: The virus amplifies and potentially spreads to secondary sites, may be asymptomatic or produce early nonspecific symptoms.
- Viral Assembly: Structural proteins, genomes, and viral enzymes assemble into new virions.
- Release: Viruses are expelled through cell lysis, exocytosis, or budding without necessarily killing the host cell.

Infection Types

Abortive Infection: A failed infection, resulting from viral mutants that do not replicate.
Persistent Infection: Ongoing viral replication without cell death; can be chronic, latent, or recurrent.
- Chronic: Non-lytic, productive.
- Latent: Limited viral activity with no synthesis.
- Recurrent: Cycles of latency followed by virus production.
- Transforming: Oncogenic viruses leading to cellular immortalization.

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Description

This quiz covers fundamental concepts in virology, including the structure and characteristics of viruses. You'll explore the contributions of key figures like Dmitri Iwanowski and learn about the essential components of viral particles. Test your knowledge on the smallest filterable organisms and their unique traits.