Chapter 6; Viruses Overview HARD

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Questions and Answers

Which type of nucleic acid is NOT found in viruses?

Triple-stranded RNA (correct)

Double-stranded DNA

Circular RNA

Single-stranded RNA

What characteristic distinguishes helical capsids from icosahedral capsids?

Size of the virus

Type of host organism

Shape of the protein coat (correct)

Presence of nucleic acid

Which term refers specifically to the type of organism a virus can infect?

Host range (correct)

Tissue specificity

Morphology

Genome type

What is the role of +ssRNA in viral replication?

Provides the code for protein synthesis Signup and view all the answers

What happens during the maturation stage of bacteriophage replication?

New phage particles are assembled Signup and view all the answers

What distinguishes virulent phages from temperate phages?

Virulent phages undergo the lytic cycle. Signup and view all the answers

What triggers a temperate phage to switch from the lysogenic cycle to the lytic cycle?

Cellular stress conditions Signup and view all the answers

What is the primary difference in penetration mechanism between enveloped and non-enveloped viruses?

Non-enveloped viruses use endocytosis; enveloped viruses fuse with the plasma membrane. Signup and view all the answers

What is meant by the uncoating process in animal virus replication?

The viral nucleic acid is released from the capsid. Signup and view all the answers

Which of the following viral nucleic acid types is used as a template for creating +ssRNA?

-ssRNA Signup and view all the answers

Which steps are correctly associated with the viral growth curve?

Inoculation, Eclipse, Burst Signup and view all the answers

What mechanism does a retrovirus use to produce DNA from its RNA?

Reverse transcriptase Signup and view all the answers

What distinguishes continuous cell lines from primary cell cultures?

Continuous cell lines do not undergo contact inhibition Signup and view all the answers

Which of the following compounds is used to block viral penetration or uncoating?

Amantadine Signup and view all the answers

What is true about viroids?

They are associated with diseases in crop plants Signup and view all the answers

How are bacteriophages typically cultivated?

In a bacterial lawn Signup and view all the answers

Which statement accurately describes prion proteins?

PrPsc is an abnormal, misfolded prion Signup and view all the answers

What are plaques in the context of bacteriophage cultivation?

Clear zones in bacterial lawns resulting from phage activity Signup and view all the answers

What is characteristic of virusoids?

They require a helper virus for replication Signup and view all the answers

Which of the following is not a target for antiviral drug action?

Inhibition of protein synthesis Signup and view all the answers

Study Notes

Acellular Pathogens: Viruses

Definition: Viruses are submicroscopic, infectious, parasitic, and non-living agents. They consist of nucleic acid (DNA or RNA, which can be double-stranded, single-stranded, circular, or linear) surrounded by a protein coat (capsid).
Capsids: Viruses have three structural forms for their capsid: helical, icosahedral, or complex (a combination of the first two).
Host Range: This refers to the range of organisms a virus can infect. Tissue specificity within a host is also important, as different viruses can target specific tissues or organs (e.g., nervous system). Examples include smallpox (humans) and bacteriophages (certain bacterial species).
Classification Criteria: Viruses are classified based on factors including the host organism, morphology (capsid structure), and genome type.
+ssRNA vs. –ssRNA: +ssRNA directly acts as a messenger for protein synthesis. –ssRNA requires a template to be converted to +ssRNA for protein synthesis.

Bacteriophages

Definition: Bacteriophages are viruses that infect and replicate within bacterial cells.
Replication Steps: Bacteriophage replication proceeds through five phases:
- Attachment: The phage attaches to the host bacterium.
- Penetration: Viral DNA enters the host cell.
- Biosynthesis: The phage's DNA replicates, and its proteins are produced.
- Maturation: New phage particles are assembled.
- Lysis: The host cell is broken open (lysed), releasing newly assembled phages. The capsid does not enter the cytoplasm during this process.
Virulent vs. Temperate Phages:
- Virulent Phages: Undergo a lytic cycle, resulting in the cell's death.
- Temperate Phages: Undergo a lysogenic cycle, where they incorporate their DNA into the host chromosome and replicate along with the host cell. These remain latent until activation (i.e., stress). Stress can trigger the switch to a lytic cycle.

Animal Virus Replication

Differences from Bacteriophages: Animal virus replication differs from bacteriophage replication significantly. Primarily in that there the entire virus, not just the nucleic acid, may enter the cytoplasm.
Uncoating: This is the process by which the viral nucleic acid is released from the protein coat within the host cell.
Penetration Mechanisms:
- Enveloped Viruses: Fuse with the host cell's plasma membrane to release their nucleocapsid.
- Non-enveloped Viruses: Are taken in by endocytosis into the host cell.
+ssRNA and –ssRNA Replication (Animal Viruses):
- +ssRNA: Directly used by the host cell's ribosomes to synthesize proteins.
- –ssRNA: Requires creation of the complementary +ssRNA as a template before protein synthesis is possible.
Release Mechanisms:
- Enveloped: Budding from the host cell membrane, or direct extrusion.
- Non-enveloped: Lysis of the host cell.

Retroviruses & Others

Retroviruses: RNA viruses that use reverse transcriptase to produce DNA from their RNA.
Viral Growth Curve: The process of viral replication in a host cell that stages as inoculation, eclipse, and burst (release into the medium). Burst size is the maximum number of virions produced per bacterium.
Animal Virus Cultivation: Viruses can be cultivated in:
- Fertilized Chicken Eggs:
  - Amniotic cavity
  - Chorioallantoic membrane
  - Yolk sac
- Cell Cultures:
  - Primary: Isolated from animal tissues, have a limited lifespan and limited number of divisions. Affected by contact inhibition. The ability to grow stops as the cells begin to touch one another.
  - Secondary: Developed from primary cell cultures, grow longer than primary, but are still limited.
  - Continuous: Derived from transformed cells (tumors), can be subcultured indefinitely without limitations. Not affected by contact inhibition.
Bacteriophage Cultivation: Grown on a bacterial lawn (dense layer of bacterial cells).
Plaques: Clear zones in a bacterial lawn, indicating areas where the bacteria have been killed by the phage.
Virus Detection: By looking for changes in the host cell (cytopathic effects), for example:
- Cytopathic Effects (CPEs):
  - Syncytia: Fusion of host cells into multinucleated giant cells.
  - Cell inclusions: Accumulations of viral proteins or substances forming structures within the cell.
Virioids: Non-infectious, single-stranded RNA molecules that cause plant diseases. They need a host to replicate but do not encode proteins to do it themselves.
Virusoids: Infectious single-stranded RNA molecules needing a helper virus for replication. They do not encode proteins.
Prions: Infectious, self-replicating proteins causing diseases. They are misfolded forms of normal cellular proteins (PrP^C and PrP^Sc). PrP^Sc converts normal PrP^C into the pathogenic form, causing the diseases by accumulating in the CNS. Prion diseases are spread through the conversion process.
Antiviral Drugs: Some drugs block viral steps, for example: penetration/uncoating, genome replication, or virion maturation/release. Examples of antiviral drugs are given.

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Description

This quiz covers the essentials of acellular pathogens, specifically focusing on viruses. You will learn about their definitions, structural forms, host range, and classification criteria, along with important distinctions between +ssRNA and -ssRNA. Test your knowledge on these key concepts and enhance your understanding of viral biology.