Definition of Viruses

Questions and Answers

What is a defining characteristic of viruses in terms of their replication?

They replicate only inside the living cells of a host organism. (correct)

They reproduce independently of host cells.

They can replicate using their own energy metabolism.

They contain ribosomes for protein synthesis.

Which of the following features differentiates viruses from bacteria?

Presence of single nucleic acid (correct)

Ability to grow independently

Enzymatic energy metabolism

Presence of ribosomes

Which of the following statements is true about the immune response to viruses?

Prions do not trigger an immune response.

Viruses do not elicit any immune response.

Bacteria trigger a stronger immune response than viruses.

Viruses can provoke an immune response. (correct)

What substance is lacking in the structure of viruses, which is essential for their function?

Ribosomes Signup and view all the answers

In what way are prions fundamentally different from viruses?

Prions do not have an incubation time. Signup and view all the answers

Which of the following is NOT a characteristic feature of viruses?

Single-celled structure Signup and view all the answers

How do viruses acquire the capability to reproduce?

By utilizing the genetic material of the host. Signup and view all the answers

What is implied by the absence of ribosomes in viruses?

Viruses require a host to translate their genetic code into proteins. Signup and view all the answers

What is the first critical step for a virus to initiate infection in a host cell?

Attachment to surface receptors on the susceptible host cell Signup and view all the answers

Which process describes the method by which enveloped viruses enter host cells?

Fusion of viral envelope with plasma membrane Signup and view all the answers

After attachment, how does a virus typically enter a cell?

Via endocytosis and vesicle formation Signup and view all the answers

What does the term 'uncoating' refer to in the viral life cycle?

The release of viral nucleic acid suitable for transcription Signup and view all the answers

What determines the host range and tissue tropism of viral species?

The interaction between virus and host cell surface receptors Signup and view all the answers

Which of the following statements about viral receptor binding is correct?

Some viruses have multiple ligand molecules that can bind to different receptors. Signup and view all the answers

What role does acidification of vesicles play in viral entry into cells?

It leads to the degradation of viral structures. Signup and view all the answers

Which type of viral entry allows direct introduction of viral genomes into the cytoplasm?

Direct penetration through channels Signup and view all the answers

What is a disadvantage of using specific phages for bacterial infections?

They may not affect all subspecies of bacteria. Signup and view all the answers

Which of the following statements regarding mycoviruses is true?

Mycoviruses selectively infect fungi. Signup and view all the answers

Which clinical issue can phage therapy address effectively?

Bacterial infections unresponsive to antibiotics. Signup and view all the answers

What is a cytopathic effect (CPE) observed during viral infections?

Lysis of host cells leading to plaques. Signup and view all the answers

What occurs during the formation of inclusion bodies in virus-infected host cells?

It signifies the presence of viral replication. Signup and view all the answers

What is a common outcome of viral infection in host cells?

Proliferation of the viral particles. Signup and view all the answers

Cell fusion caused by some viral infections results in what phenomenon?

Formation of multinucleated giant cells. Signup and view all the answers

How do phages improve their chances of success in treating bacterial infections?

By applying mixtures of phages. Signup and view all the answers

What is the primary purpose of using a bicarbonate buffering system in cell culture medium?

To stabilize physiological pH Signup and view all the answers

What is the typical duration for incubating cell cultures when suspecting viral presence?

1 to 4 weeks Signup and view all the answers

Which of the following is NOT a characteristic of primary cell cultures?

They can be maintained indefinitely Signup and view all the answers

What does a cytopathic effect (CPE) indicate during cell culture inspection?

Presence of the virus Signup and view all the answers

Which type of cell culture can be indefinitely maintained through serial subculture?

Continuous cell lines Signup and view all the answers

Which of the following cell lines is derived from a human carcinoma?

HEP-2 Signup and view all the answers

What kind of cells are utilized for the production of vaccines?

Primary cell cultures Signup and view all the answers

Which of the following statements about phenol red is accurate?

It indicates pH changes in culture medium Signup and view all the answers

What is the role of endolysin in the lytic cycle of bacteriophages?

It damages the cell wall of the host cell. Signup and view all the answers

In what phase does the bacteriophage inject its genetic material into the host cell during the lytic cycle?

Injection stage Signup and view all the answers

During which stage of the lytic cycle does the phage DNA/RNA commandeer the host cell's machinery?

Early infection stage Signup and view all the answers

What happens to the host cell at the completion of the lytic cycle?

It undergoes lysis and releases new phage particles. Signup and view all the answers

Which component does NOT assemble during the replication stage of the lytic cycle?

Host cell enzymes Signup and view all the answers

What distinguishes the lysogenic cycle from the lytic cycle?

The lysogenic cycle integrates viral DNA into the host genome. Signup and view all the answers

What triggers the transition from the lysogenic cycle back to the lytic cycle?

Exposure to harmful environmental factors Signup and view all the answers

Which of the following viruses acquires its envelope from the nuclear membrane?

Herpes virus Signup and view all the answers

Study Notes

Definition and Characteristics of Viruses

A virus is an ultramicroscopic infectious agent that replicates only inside living cells of an organism.
Viruses infect a wide range of life forms, including animals, plants, and microorganisms such as bacteria and archaea.
Found in nearly every ecosystem on Earth, viruses are the most numerous biological entities.
All viruses are potentially infectious and possess a single type of nucleic acid.
Viruses cannot grow independently and rely solely on the host for reproduction.
Lack enzymes for energy metabolism, ribosomes, and necessary genetic information for enzyme and ribosomal protein synthesis.

Differences Among Viruses, Bacteria, Fungi, and Prions

Viruses require a host for reproduction, while prions lead to long-lasting diseases without inducing immune responses.
Viruses attach to specific receptors on host cells to initiate infection, with interactions determining host range and tissue tropism.
Penetration into host cells varies: receptors-mediated endocytosis, fusion of the viral envelope, or direct introduction of viral genomes.

Bacterial and Viral Interactions

Bacteriophages are viruses that infect bacteria, utilizing two main reproduction cycles: the lytic cycle and the lysogenic cycle.
Lytic Cycle involves:
- Attachment to bacterial surface proteins and injection of phage DNA/RNA.
- Host cell's organelles are commandeered to produce viral proteins and new phage particles.
- Host cell lysis releases new phages to infect other bacteria.
Lysogenic Cycle allows phages to integrate their genome into the host DNA, replicating passively through host cell divisions.

Mycoviruses and Fungal Interactions

Mycoviruses are viruses that selectively infect fungi and have been recognized since the 1960s.

Effects of Viral Activities on Host Cells

Viral infection can lead to cytopathic effects, altered cell functions, or host cell proliferation.
Cytopathic Effects (CPE) result from viral lysis of host cells, visible as clear zones or plaques.
Inclusion Bodies formed during viral replication may help diagnose infections like smallpox or poliomyelitis.
Some infections cause Cell Fusion, resulting in merged infected cells, detectable through specific culture conditions.

Cell Culture Techniques for Virus Study

Primary Cell Cultures: Normal cells from animals or humans that grow limited passages, essential for virus isolation and vaccine production. Examples include monkey kidney and human amnion cell cultures.
Continuous Cell Lines: Derived from cancer cells, enabling indefinite serial culture, useful for viral identification but not for vaccine production. Examples include HeLa and Vero cell lines.

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Description

This quiz explores the definition and characteristics of viruses as ultramicroscopic infectious agents. Understand how viruses interact with living cells in various organisms, including animals, plants, and microorganisms. Test your knowledge on the vital role viruses play in biology.