Microbiology Chapter on Viruses

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Questions and Answers

Which of the following characteristics is NOT true for all viruses?

They are obligatory intracellular parasites.

They can multiply by using the host cell's synthesizing machinery to cause the synthesis of specialized elements that can transfer the viral nucleic acid to other cells.

They can replicate independently of a host cell. (correct)

Viruses contain either DNA or RNA, never both.

The 'host range' of a virus refers to:

The size range of host cells the virus can infect.

The specific species of bacteria a virus can infect.

The spectrum of host cells in which a virus can multiply. (correct)

The number of times a virus can replicate within a single host cell.

What is the protein coat surrounding the nucleic acid of a virus called?

Viroid

Prion

Envelope

Capsid (correct)

What is the difference between the 'capsid' and the 'envelope' of a virus?

The capsid is composed of proteins, while the envelope is composed of lipids, proteins, and carbohydrates. (A) Signup and view all the answers

What is the name for a complete, fully developed viral particle, composed of a nucleic acid surrounded by a coat?

Virion (A) Signup and view all the answers

How is viral size typically determined?

Using an electron microscope. (A) Signup and view all the answers

What is the range of sizes for viruses?

20-1000nm (D) Signup and view all the answers

What is a capsomere?

A subunit of the capsid. (D) Signup and view all the answers

What is a distinguishing characteristic of a latent viral infection?

The virus remains dormant within the host cell for an extended period without causing symptoms. (D) Signup and view all the answers

What is the primary cause of prion-related diseases?

Misfolded proteins. (D) Signup and view all the answers

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

They typically cause the production of anti-viral proteins in the host plant. (D) Signup and view all the answers

Which of the following are NOT challenges associated with fulfilling Koch's Postulates for viruses?

Viruses can be transmitted through contaminated water sources. (A) Signup and view all the answers

What is the main difference between a virus and a viroid?

Viruses are always associated with a protein coat, while viroids are not. (D) Signup and view all the answers

What is the function of a virion?

To transport the viral nucleic acid to other cells. (B) Signup and view all the answers

What is a characteristic of persistent viral infections?

The virus remains in the host for a long period of time, often without causing symptoms. (C) Signup and view all the answers

Which of the following is NOT a reason why the study of SIV and FIV is valuable?

They can be easily transmitted between different species. (A) Signup and view all the answers

Which of the following viruses has a helical structure?

Tobacco mosaic virus (B) Signup and view all the answers

Why can the genes that code for proteins in viruses often serve two functions?

Viruses have limited space within their genetic material. (B) Signup and view all the answers

Which of the following viral families has a genome composed of double-stranded RNA?

Reoviridae (A) Signup and view all the answers

What is a distinguishing feature of enveloped viruses?

They have an outer membrane derived from the host cell. (D) Signup and view all the answers

Prophages and proviruses are similar to plasmids in that they can:

Be replicated with the cell's chromosome. (A) Signup and view all the answers

What is the primary function of the + strand in a double-stranded RNA virus?

It acts as mRNA for protein synthesis. (B) Signup and view all the answers

Which viral family uses reverse transcriptase to synthesize DNA from RNA?

Retroviridae (D) Signup and view all the answers

What is the primary function of the RNA-dependent RNA polymerase in Picornaviridae?

Transcribing mRNA from the + strand RNA (D) Signup and view all the answers

Which of the following statements about prophages is TRUE?

Prophages can cause the host cell to produce new viruses. (B) Signup and view all the answers

How does the host cell's DNA become integrated with the genetic material of oncogenic viruses?

Viral enzymes, such as reverse transcriptase, transcribe viral RNA into DNA, which then integrates into the host cell's genome. (A) Signup and view all the answers

A patient presents with symptoms suggestive of a viral infection. What would be the most likely indicator of a viral etiology?

Presence of antibodies against a specific virus. (B) Signup and view all the answers

Which of the following methods is NOT typically used to cultivate viruses for research?

Growth in nutrient-rich broth. (B) Signup and view all the answers

Which of the following is NOT a characteristic of transformed cells?

Production of antibodies specific to the virus (D) Signup and view all the answers

Which family of viruses is associated with Burkitt's lymphoma and nasopharyngeal carcinoma?

Herpesviridae (C) Signup and view all the answers

How does the ability of a virus to produce tumors relate to the production of reverse transcriptase?

Reverse transcriptase is needed for the virus to integrate its genetic material into the host cell's DNA, potentially leading to oncogenesis (D) Signup and view all the answers

Which of the following viral families is NOT associated with oncogenic properties?

Picornaviridae (C) Signup and view all the answers

During the lytic cycle, what happens to the host cell after the phage DNA is injected?

The host cell is destroyed and releases new phage particles. (C) Signup and view all the answers

Which statement accurately describes the process of penetration during the lytic cycle?

Phage DNA is injected into the host cell, while the capsid remains outside. (B) Signup and view all the answers

What is the primary function of the repressor protein produced by the prophage during the lysogenic cycle?

To prevent the expression of the prophage genes and maintain lysogeny. (C) Signup and view all the answers

Which of the following is a characteristic of the lysogenic cycle that distinguishes it from the lytic cycle?

The phage DNA is replicated along with the host cell's DNA. (A) Signup and view all the answers

How does lysogeny lead to phage conversion?

By integrating phage DNA into the host cell's genome, the phage can contribute to the host cell's phenotype. (D) Signup and view all the answers

What is the primary difference between generalized and specialized transduction?

Generalized transduction can transfer any bacterial genes, while specialized transduction transfers only a specific set of genes. (B) Signup and view all the answers

How do animal viruses enter host cells?

Through endocytosis or fusion with the cell membrane. (A) Signup and view all the answers

What is the role of capsid proteins in the multiplication of animal viruses?

To protect the viral DNA or RNA during entry and transport within the host cell. (C) Signup and view all the answers

What is the name given to the area of lysis surrounding a single viral particle on a nutrient agar plate?

Plaque (B) Signup and view all the answers

Which of the following viral families would NOT typically be found with an enveloped structure?

Adenoviridae (C) Signup and view all the answers

What is the primary reason that viruses need to be grown in living cells?

All of the above. (D) Signup and view all the answers

Which of the following is NOT a technique used to identify viruses?

Microscopy (D) Signup and view all the answers

What is the name given to a group of viruses that share the same genetic information and ecological niche?

Species (D) Signup and view all the answers

Which of the following is NOT true about cultivation of animal viruses?

Animal viruses can be easily cultivated in laboratory media, similar to bacterial growth. (B) Signup and view all the answers

What is the general purpose of using a plaque assay for bacteriophages?

To quantify the concentration of bacteriophages in a sample. (B) Signup and view all the answers

Which of the following describes a characteristic of the morphology of complex viruses?

They have a polyhedral capsid with a helical tail attached. (B) Signup and view all the answers

Study Notes

Learning Objectives

Differentiate a virus from a bacterium
Describe the chemical and physical structure of enveloped and nonenveloped viruses
Define viral species
Provide an example of a family, genus, and common name for a virus
Describe how bacteriophages are cultured
Describe how animal viruses are cultured
List three techniques used to identify viruses
Describe the lytic cycle of T-even bacteriophages
Describe the lysogenic cycle of bacteriophage lambda
Compare and contrast the multiplication cycle of DNA and RNA-containing animal viruses
Define oncogene and transformed cell
Discuss the relationship between DNA- and RNA-containing viruses and cancer

Check Your Understanding

How did the small size of viruses aid in their detection before electron microscopes?
Diagram a non-enveloped polyhedral virus with spikes
Differentiate virus species from bacterial species
Provide the correct family and genus for HPV, along with a completed name for example.
Explain the plaque method
Explain why continuous cell lines are more practical for culturing viruses than primary cell lines
Explain tests that can identify influenza virus
Explain how bacteriophages obtain nucleotides and amino acids without metabolic enzymes
Describe lysogeny in Vibrio cholerae
Describe the principal events of enveloped DNA virus attachment, entry, uncoating, biosynthesis, maturation, and release
Define provirus
Explain how an RNA virus can cause cancer without DNA insertion

Viral Structure

A virion is a complete viral particle composed of nucleic acid surrounded by a coat
Viruses contain either DNA or RNA (never both), which can be single or double stranded, linear or circular, or divided into multiple molecules
The proportion of nucleic acid relative to protein in viruses ranges from 1% to 50%
The protein coat surrounding the nucleic acid is called a capsid, which is composed of subunits called capsomeres
Some viruses have an envelope consisting of lipids, proteins, and carbohydrates surrounding their capsid
Some envelopes contain spike like structures (carbohydrate-protein complexes)
Helical viruses have a hollow cylinder shape
Polyhedral viruses have a many-sided structure (often icosahedral)
Enveloped viruses have a pleomorphic spherical shape

Growing Bacteriophages/Animal Viruses

Bacteriophages are grown using a plaque method involving mixing them with host bacteria and nutrient agar
Animal viruses are sometimes grown in whole animals, or embryonated eggs, or in cell cultures (primary cell lines/embryonic diploid cell lines)
Viral growth can sometimes be seen as cytopathic effects in cell cultures

Viral Identification

Viral identification often involves serological tests
Viruses/proteins can be identified via PCR and RFLPs

Viral Multiplication

Viruses lack the enzymes necessary for energy production and protein synthesis; viral multiplication relies on the host cell's machinery
Lytic cycle: Phage causes lysis and death of the host cell
Lysogenic cycle: Phage DNA is incorporated into the host cell's DNA as a prophage.
Animal virus multiplication: Viruses attach, enter, uncoat, replicate, assemble & release
DNA viruses generally replicate in the nucleus, while RNA viruses typically do so in the cytoplasm
RNA viruses can include RNA dependent RNA polymerase

Viruses and Cancer

Oncogenic viruses cause cancer
Some DNA viruses are oncogenic, like those within the Adenoviridae, Herpesviridae, Poxviridae, Papovaviridae families
EBV is a herpesvirus that can cause Burkitt's lymphoma and nasopharyngeal carcinoma
Hepadnavirus are associated with liver cancer
Retroviruses are also oncogenic

Latent and Persistent Infections

Latent viral infection: The virus remains in the host cell without producing infection, like cold sores or shingles
Persistent viral infection: Virus occurs over a long period and is fatal

Prions

Infectious proteins that cause degeneration of brain tissue (e.g., CJD, mad cow disease)
Result from altered proteins (either a mutation or interaction w/ altered protein)

Plant Viruses and Viroids

Plant viruses enter hosts via wounds or parasites (like insects)
Viroids are infectious RNA molecules that cause plant diseases (e.g., potato spindle tuber disease)

Clinical Applications

Viruses can be studied by using tissue cultures and animal models.
Virus identification is often done using serological tests.
There are numerous viruses, and viral infection can cause a wide range of diseases or symptoms that are sometimes detected (e.g., hepatitis viruses and encephalitis).

Studying That Suits You

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Description

Test your knowledge on the essential aspects of viruses in microbiology. This quiz covers the differentiation between viruses and bacteria, their structures, life cycles, and associations with cancer. Perfect for reinforcing your understanding of viral classification and culture techniques.