Virology Quiz on Polyomaviruses

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Questions and Answers

What is the primary role of histones in polyomaviruses?

To facilitate viral entry into host cells

To organize the viral genome into nucleosomes (correct)

To create a lipid bilayer

To protect the viral envelope

Which component is NOT typically associated with the viral envelope?

Lipid membrane from the host cell

Glycoprotein spikes

Oligosaccharides linked with glycoproteins

Capsid proteins (correct)

What describes the relationship between viral membranes and nucleocapsids in certain viruses?

Nucleocapsids do not interact with membranes

The membrane lies beneath the capsid in some viruses (correct)

The capsid is derived from the host cell

The membrane is always external to the capsid

Which statement is true about the glycoprotein spikes found on viral envelopes?

They include transmembrane helixes Signup and view all the answers

What best describes the genomic organization of polyomaviruses like simian virus 40?

Circular double-stranded DNA Signup and view all the answers

What is the significance of oligosaccharides linked to glycoproteins in viruses?

They assist in viral entry and immune evasion Signup and view all the answers

Which structure is critical for maintaining the integrity of viral particles?

The capsid Signup and view all the answers

What role does the lipid bilayer play in enveloped viruses?

It forms the outermost layer and is involved in host cell interaction Signup and view all the answers

What function does the N protein serve in the context of viral RNA?

It binds to RNA to form a protective complex. Signup and view all the answers

What property is characteristic of the lipid envelope in certain viruses?

It provides a barrier against the host immune system. Signup and view all the answers

How do viruses typically enter host cells?

By utilizing receptor-mediated endocytosis. Signup and view all the answers

Which aspect of viral structure is vital for its recognition by host cells?

The specific arrangement and composition of viral proteins. Signup and view all the answers

What is the significance of the ribose-phosphate backbone in viral RNA structure?

It protects the RNA from degradation. Signup and view all the answers

Which statement accurately describes genomic organization in many viruses?

Genomic organization can be segmented or unsegmented. Signup and view all the answers

What is one role of specialized viral proteins during the packaging of the nucleic acid genome?

They form a protective shell around the nucleic acid. Signup and view all the answers

Why is the structure of the viral complex significant in the context of viral infection?

It influences the virus's ability to infect specific host cells. Signup and view all the answers

What is the primary reason viruses utilize a symmetrical structure for their capsid?

To create a stable structure while using minimal genetic resources. Signup and view all the answers

What does the term 'triangulation number' (T) signify in the context of viral capsids?

The number of triangular faces formed by the subunits in a capsid. Signup and view all the answers

How do head-to-head and tail-to-tail interactions contribute to the viral capsid structure?

They help subunits fit together tightly, creating a stable closed structure. Signup and view all the answers

Why is it essential for viruses to have a limited amount of genomic material?

To maintain a compact structure while ensuring survival in diverse environments. Signup and view all the answers

What is a primary characteristic of icosahedral capsids used by viruses?

They consist of repeated subunits providing symmetrical stability. Signup and view all the answers

What does it mean for a virus to have an efficient capsid structure?

It can protect the viral genome while using minimal resources. Signup and view all the answers

In terms of viral structure, what do identical subunits enclose?

The virus's genetic material. Signup and view all the answers

Which of the following best describes the function of repeated structural proteins in viral capsids?

They form a compact and stable structure to protect genetic information. Signup and view all the answers

Study Notes

Viral Structures and Symmetries

Helical symmetry: Virus particles formed from a single protein subunit arranged in a spiral structure. A 10 nm axial rise indicates the vertical distance the helix moves upward after a full rotation. Three protein subunits are required to make one full turn (μ = 3).
Tobacco Mosaic Virus (TMV): Axial rise per subunit is typically around 0.14 nm; number of subunits per turn (n) is 16.3.
Vesicular Stomatitis Virus (VSV): The N protein (nucleoprotein) wraps around the viral RNA, forming a helical structure. The scale bar of 100 Å represents the nucleocapsid diameter.

Enveloped RNA Viruses

Paramyxoviridae (Measles and Mumps viruses): Nucleocapsid surrounded by a lipid envelope studded with glycoproteins.
Rhabdoviridae (Rabies virus): Bullet-shaped with a nucleocapsid tightly coiled inside.
Orthomyxoviridae (Influenza virus): Contain segmented RNA genomes wrapped by nucleoproteins, forming multiple helical nucleocapsids. The genome is surrounded by the viral matrix protein, and the RNA polymerase complex (PB2, PB1, PA) helps initiate transcription.
Filoviridae (Ebola viruses): Filamentous structure with RNA genome tightly packed into a helical nucleocapsid.

Icosahedral Symmetry

Watson and Crick: Spherical capsids built with icosahedral symmetry (20 triangular faces, 12 vertices, 30 edges). This minimizes genetic material needed while maximizing stability.
Icosahedron: A Platonic solid, characterized by 5-fold, 3-fold, and 2-fold symmetry axes.

Viral Capsid Complexity

Triangulation number (T): Represents the complexity of the capsid's arrangement—how many subunits form one triangular face. T=1 is the simplest, whereas T=3 and higher values indicate more complex structures.
Quasiequivalence: Subunits in a capsid higher than T=1 occupy similar but not identical positions.
Adeno-associated virus 2: An example of a T=1 icosahedral structure.

Viral Proteins and Functions

Nucleocapsid: The core that encapsulates viral RNA, composed of nucleoprotein bound to RNA.
Lipid envelope: Acquired from host cell membranes during viral replication; embedded with viral glycoproteins for attachment and entry.
Spike proteins (S): Protrude from the surface; give virus its crown-like appearance. Critical for attachment to host cells.
Adenovirus structure: Follows T=25 icosahedral symmetry; contains 720 copies of the viral hexon protein (major component of the capsid). Fibers at 12 vertices aid in host cell attachment.
Herpes Simplex Virus (HSV) capsid: Highly organized structure with multi-viral proteins (VPs) and a specialized portal for DNA/RNA entry/exit.
Viral proteins (VPs): Varies by specific virus; major structural components for forming capsids and playing roles in genome packaging, assembly and functions.

Genome Packaging

Viral genomes are highly condensed, often analogous to packing wire into a tennis ball for optimal confinement.
Some viruses use specialized viral proteins, or cellular proteins like histones, to package the genome.
Structures of viral genomes: Linear, circular, gapped, segmented, single-stranded (+ or - strand), double-stranded, and ambisense characteristics.

Viral Genomes and Types

RNA and DNA-based genomes. RNA genomes appeared before DNA in evolution (RNA World), and DNA genomes are generally more complex.
Baltimore system: Seven types of genomes and descriptions, such as linear, circular, gapped, segmented, single-stranded, double-stranded, and ambisense, based on the relationship to mRNA.
Viral genome diversity is critical for viral function.

Genome Replication and Viral Protein Synthesis

Viral genomes code for unique methods such as ribosomal frameshifting, IRES-related translation of nested mRNAs, and polyprotein processing.
There are many varieties of viral enzymes including polymerase, transcriptases, proteases, helicases, and ligase.
Viral genomes are structurally diverse to encode, package, transcribe and translate unique proteins for replication and expression.

Other Viral Components

Viral proteins not directly part of structure, but involved in functions such as:
- Nucleic acid replication, transcription, and translation
- Host cell function shutdown
- Inhibition of innate immunity.
- Cellular machinery interference
- Synthetic activities

Viral DNA Genomes

dsDNA viruses dominate the bacterial virosphere; many DNA viruses emulate the host, based on DNA.
However, almost all viral DNA genomes are NOT like cell chromosomes, but have evolved unexpected, unique tricks for replication.

ssDNA Genomes

Circular or linear forms with a single strand.

RNA Genomes

RNA viruses dominate eukaryotic virosphere (rare in bacteria), have their own RdRp (RNA-dependent RNA polymerase) enzymes.

Other Viral Structures

Enveloped viral structures, with envelopes formed from host cell membranes, contain viral proteins, glycoproteins, and oligosaccharides.
Viral membrane interactions using glycoproteins and internal domains.
Multiple glycoprotein spike structures.

Viral Mutations and Genetic Methods

Mutations: Changes in nucleic acids and proteins; these changes can alter viral function but have not been altered in the past.
Genetic methods for virus manipulation: Transfection to introduce specific DNA to cultures or cells. Cloning techniques for manipulating viral DNA sequences.

Large Virus Groups

Bacteriophage T4: A large virus with multiple structural elements for various functionalities such as head, connector, tail sheath, whiskers, tail fibers, and baseplate.
Herpesviruses: Large viruses with specific protein subunits to produce a nucleocapsid, tegument envelope, and envelope.
Poxviruses: Large viruses with dumbbell-shaped cores and specific layering membranes.
Pithovirus: Large virus observed using electron microscopy.

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Description

Test your knowledge on polyomaviruses and their structures with this quiz. Explore the roles of histones, viral envelopes, and glycoproteins in these unique viruses. Each question focuses on key aspects of their genomic organization and integrity.