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Questions and Answers
What is a primary function of regulator proteins in viral biosynthesis?
What is a primary function of regulator proteins in viral biosynthesis?
Where do most dsDNA viruses replicate, except for Poxviruses?
Where do most dsDNA viruses replicate, except for Poxviruses?
Which type of RNA virus can directly act as viral mRNA?
Which type of RNA virus can directly act as viral mRNA?
How do naked viruses typically release progeny virions from host cells?
How do naked viruses typically release progeny virions from host cells?
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In what part of the host cell does maturation of RNA viruses primarily occur?
In what part of the host cell does maturation of RNA viruses primarily occur?
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What is the role of enzymes such as DNA/RNA polymerase in viral replication?
What is the role of enzymes such as DNA/RNA polymerase in viral replication?
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Where does the assembly of daughter virions typically take place for DNA viruses?
Where does the assembly of daughter virions typically take place for DNA viruses?
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Which mechanism is specifically associated with the release of enveloped viruses?
Which mechanism is specifically associated with the release of enveloped viruses?
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What is the primary function of a viral capsid?
What is the primary function of a viral capsid?
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Which of the following is true about the composition of a virion?
Which of the following is true about the composition of a virion?
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What distinguishes enveloped viruses from naked viruses?
What distinguishes enveloped viruses from naked viruses?
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What type of nucleic acid can be found in a viral core?
What type of nucleic acid can be found in a viral core?
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How are capsomers organized within the capsid?
How are capsomers organized within the capsid?
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What is the main characteristic that distinguishes enveloped viruses from naked viruses?
What is the main characteristic that distinguishes enveloped viruses from naked viruses?
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Which symmetry forms can a viral capsid exhibit?
Which symmetry forms can a viral capsid exhibit?
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Which viruses are characterized by helical symmetry?
Which viruses are characterized by helical symmetry?
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What is the smallest size range of viruses mentioned?
What is the smallest size range of viruses mentioned?
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Which of these statements correctly describes capsid functions?
Which of these statements correctly describes capsid functions?
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What is the role of the viral envelope in viral infections?
What is the role of the viral envelope in viral infections?
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Which of the following correctly describes the composition of complex virions?
Which of the following correctly describes the composition of complex virions?
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The spikes on a virus primarily serve which functions?
The spikes on a virus primarily serve which functions?
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What type of nucleic acid is referred to as +ssRNA?
What type of nucleic acid is referred to as +ssRNA?
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Which structure is characteristic of icosahedral symmetry in viruses?
Which structure is characteristic of icosahedral symmetry in viruses?
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Which of the following classifications is NOT used for viruses?
Which of the following classifications is NOT used for viruses?
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Study Notes
Viral Size
- Smallest living units measure from 20nm –300nm
- Largest virus is Poxvirus (300nm)
- Smallest virus is Polio and foot & mouth disease virus (20nm)
Viral Structure
- Two major types: naked nucleocapsid virus and the enveloped virus
Virion
- Complete virus particle - entire infectious unit is called Virion
- Contains DNA or RNA surrounded by a protein coat called capsid
- Some viruses’ capsid may be covered by a lipid envelope; they are called enveloped viruses
Viral Core
- Site: in the centre of the virus
- Compositions: viral nucleic acid, either DNA or RNA, may be double or single stranded
- Functions: control the viral heredity and variation, responsible for the infectivity
Capsid
- Accounts for most of the virion mass
- Subunits called protomeres aggregate to form Capsomers which in turn aggregate to form the capsid
- Site: surround the viral genome, outer of the viral core
- Compositions and arrangement:
- Protein in nature and consists of Capsomers
- Symmetry in arrangement: helical symmetry; cubic or icosahedra symmetry; complex symmetry
- Functions of viral capsid:
- protects the viral nucleic acid
- participates in the viral infection
- shares the antigenicity
Biosynthesis
- Synthesis of NA & capsid
- Production of enzymes needed for viral synthesis, assembly & release
- Regulator proteins are synthesized - Regulator proteins shut down normal host cell function
Enzymes
- Encode for:
- DNA / RNA polymerase
- Other replication enzymes
- NA replication produces new viral genomes
dsDNA Viruses
- Except Poxviruses, dsDNA viruses replicate in the nucleus
- Using host cell dependent RNA polymerase to synthesize their mRNA
- RNA viruses mainly in cytoplasm
RNA Viruses
- Three kinds:
- +ssRNA: +ssRNA virus itself can direct as viral mRNA
- -ssRNA: Use the virion RNA polymerase to synthesize viral mRNA
- Retro viruses: Use virion reverse transcriptase to synthesize a DNA copy of the viral RNA genome
- Uses the host cell RNA polymerase to synthesize viral mRNA
Maturation
- Assembly of daughter virions into capsids in host cell nucleus or cytoplasm
- Assembly of viral nucelo - capsid may take place in:
- Nucleus………………DNA viruses
- Cytoplasm…………...RNA viruses
- At cell surface….........Avian Influenza virus
- Herpes and Adenoviruses host cell nucleus
- Picorna and Poxviruses assembly occur in cytoplasm of host cell
- Accumulation of virions at sites of assembly may form inclusion bodies
Release
- Release of new intact infectious virions
- May occur by:
- Budding through cell membrane (e.g: Enveloped viruses)
- Lysis of infected host cells (e.g: Naked viruses)
Envelope
- Amorphous structure composed of lipid, and glycoprotein
- Lies to the outside of the capsid
- Contains a mosaic of antigens from the host and the virus
- Site: on the surface of some viruses
- Composition: lipid, protein, and carbohydrate
- Functions: antigenicity, infectivity, and resistance; some viruses possess neuraminidase
Spikes
- Glycoprotein projections with enzymatic and/or adsorption and/or hemagglutinating activity
- Arise from the envelope and are highly antigenic
Simple Virion (Naked Virus)
- Contain NA & capsid
Complex Virion (Enveloped Virus)
- Contain NA, capsid & envelope
+ssRNA
- Same as viral mRNA
-ssRNA
- As a template transcribe complimentary mRNA
Viral Symmetry - Shape
- Three types:
- Icosahedral (cubic)
- Helical
- Complex
- Cubic symmetry, the capsid is 20 triangular facets & 12 corners e.g.Adenovirus
- Helical symmetry- helical nucleocapsid e.g.Influenza virus
- Complex symmetry -- neither cubic nor helical symmetry, may be brick shaped. poxvirus
Classification of Viruses
- Criteria used for viral classification includes:
- Classified mainly based on nucleic acid:
- Type of nucleic acid (DNA or RNA)
- Physical construction (single / double stranded / linear / circular / segmented)
- Classified mainly based on nucleic acid:
- Baltimore Classification of Viruses
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Description
Test your knowledge on the various aspects of viral structure and size, including the types of viruses, the composition of virions, and the role of the capsid. This quiz covers essential concepts in virology that are crucial for understanding how viruses function and infect hosts.
