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Questions and Answers
Which virus family is characterized by viruses with enveloped, icosahedral capsids and double-stranded DNA?
Which virus family is characterized by viruses with enveloped, icosahedral capsids and double-stranded DNA?
Which of the following families contains viruses with single-stranded DNA?
Which of the following families contains viruses with single-stranded DNA?
What is the nucleic acid type associated with the virus family Hepadnaviridae?
What is the nucleic acid type associated with the virus family Hepadnaviridae?
Which group do Poxviridae viruses belong to based on their nucleic acid structure?
Which group do Poxviridae viruses belong to based on their nucleic acid structure?
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Which of the following statements is true regarding the adenoviruses?
Which of the following statements is true regarding the adenoviruses?
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What is a virion?
What is a virion?
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What primary role does the capsid serve in a virus?
What primary role does the capsid serve in a virus?
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Which classification accurately describes a virus that contains RNA and is capable of reverse transcription?
Which classification accurately describes a virus that contains RNA and is capable of reverse transcription?
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How do viruses replicate within a host cell?
How do viruses replicate within a host cell?
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What distinguishes bacteriophages from other types of viruses?
What distinguishes bacteriophages from other types of viruses?
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Study Notes
Virology
- Virology is the study of viruses, complexes of nucleic acids and proteins
- Viruses replicate inside animal, plant, and bacterial cells
- To replicate, viruses utilize host cell functions, acting as parasites
- All viruses are obligate intracellular parasites
- Virus replication inside host cells releases virus particles (virions)
- Virions lack metabolism and organelles
- Virions carry genetic information for new virus particle generation after infection
- Virus sizes range from 20 to 450 nanometers (nm)
Chemical Composition of Viruses
- Viruses are minute nucleoprotein particles
- They consist of a nucleic acid core (DNA or RNA, linear or circular) and a protein coat (capsid) surrounding the nucleic acid
- The protein coat is made of identical structural units called capsomeres
- Virus composition, number, and structure differ
Virus Structure
- Some viruses have an envelope of fat and protein molecules
- A virus particle outside the cell is called a virion
- Each virion contains at least one protein synthesized by specific genes in its nucleic acid
Other Virus-like Particles
- Viroids are disease-causing organisms containing only nucleic acid without structural proteins
- Prions are virus-like particles primarily composed of proteins tightly integrated with a small nucleic acid molecule
- Viruses attach to bacteria using a "tail" and proteinaceous "pins"
- The virus tail contracts, penetrating the bacterial cell wall and membrane to inject viral nucleic acids
Capsid Structure and Function
- The capsid is the protein shell enclosing the nucleic acid, also called the nucleocapsid
- The capsid is composed of protein subunits called capsomeres
- The capsid protects the nucleic acid from enzymes
- The capsid has attachment sites for host cells
- The capsid enables the virion to penetrate the host cell membrane and sometimes inject infectious nucleic acid into the cytoplasm
Virus Classification
- Viruses are classified based on the host cell they infect (animals, plants, fungi, bacteria)
- A more useful classification system is based on the nucleic acid type:
- DNA viruses are further divided into double-stranded and single-stranded types
- RNA viruses are positive-sense, negative-sense, and double-stranded
- Reverse-transcribing viruses (retroviruses) include double-stranded, and single-stranded types
- Baltimore classification groups viruses by their nucleic acid type, strandedness, sense, and replication method into seven categories
Structure, Function, and Uses of Viruses
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A virus is a small parasite that cannot reproduce independently
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Once in a susceptible cell, a virus directs cell machinery to produce more viruses
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An entire infectious virus particle (virion) comprises the nucleic acid and protein outer shell
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Simplest viruses have only enough nucleic acid to encode a few proteins (e.g., 4)
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Complex viruses can encode many proteins (e.g., 100-200)
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DNA viruses typically use cellular enzymes in DNA/mRNA synthesis
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All viruses use normal cellular ribosomes, tRNAs, and translation factors in protein synthesis
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Most viruses utilize the cellular machinery for macromolecular synthesis during the infection phase, directing it to synthesize a limited number of viral mRNAs and proteins instead of the thousands of normal cellular macromolecules
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Description
Explore the essential concepts of virology, including virus structure, composition, and replication. This quiz covers the nature of viruses as intracellular parasites and the characteristics that define them. Test your knowledge of these microscopic entities and their impact on living organisms.
