Questions and Answers
What term is used to describe a virus in its extracellular state?
Which type of virus is characterized by the absence of a phospholipid membrane?
What part of the virus protects the viral genome during transfer between host cells?
How do viruses reproduce once they have invaded a host cell?
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Which structural component of viruses is specifically involved in assembling new virions?
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What are the three primary shapes of viruses according to their capsid symmetry?
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Which type of virus includes herpesviruses and HIV?
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What eliminates the capsid of a virus once it enters a host cell?
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What structure do helical viruses possess that provides a central cavity for nucleic acid?
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Which of the following viral shapes is characterized by equilateral triangles forming a spherical structure?
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What type of virus uses its tail to inject DNA into a bacterial host cell?
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What is the primary reason for the higher mutation rates observed in RNA viruses as opposed to DNA viruses?
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What phase do viruses enter when their capsid is removed and they become active?
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Which component protects the viral genome and aids in its transfer between host cells?
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In what form can the viral genetic material exist?
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What term is used to describe the total genetic content of a virus?
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What type of viral structure has a combination of helical and icosahedral shapes?
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During which process does the viral DNA utilize the host's DNA polymerase?
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Study Notes
Overview of Viruses
- Viruses are acellular pathogens with a simple structure and lack cytoplasmic membranes, cytosol, or organelles.
- They can infect all types of cells, including bacterial cells (bacteriophages).
- Viruses depend on host cells for metabolic processes and reproduction.
Virus Structure and States
- Extracellularly, viruses exist as virions, which are inactive and cannot reproduce.
- A virion is composed of a capsid (protein coat) that surrounds a nucleic acid core, containing the viral genome.
- Nucleocapsid refers to the combination of the nucleic acid and the capsid.
- Some virions possess an enveloped layer (phospholipid membrane) derived from the host cell, classifying them as enveloped viruses (e.g., herpesviruses, HIV).
- Non-enveloped or naked viruses (e.g., poliovirus) lack this outer membrane.
Intracellular Virus Activity
- Once inside a host cell, the virus sheds its capsid and enters the intracellular state as active nucleic acids.
- Viral nucleic acids instruct the host to synthesize viral components, leading to virion assembly.
Capsid Symmetry and Virus Shapes
- Viruses exhibit various capsid symmetries, which lead to different shapes:
- Helical Viruses: Capsid forms a hollow tube that encases the nucleic acid. Example: Tobacco mosaic virus.
- Icosahedral Viruses: Spherical shape formed by fused equilateral triangles. Release occurs upon host cell lysis. Examples: Poliovirus, rhinovirus, adenovirus.
- Complex Viruses: Combination of icosahedral and helical shapes, often observed in bacteriophages, which have a unique head-tail morphology.
Viral Genetic Material
- Viral genomes contain either DNA or RNA and are often small, encoding only a few essential proteins.
- The genetic material can be single-stranded or double-stranded, linear or circular.
Replication Mechanism
- DNA Viruses: Viral DNA enters the nucleus, uses host DNA polymerase for replication and mRNA synthesis, leading to protein formation.
- RNA Viruses: Many replicate in the cytoplasm, using host ribosomes to translate viral RNA into proteins, which include RNA polymerase for further genome replication.
- RNA polymerases are prone to transcription errors, resulting in higher mutation rates in RNA viruses compared to DNA viruses.
Summary of Key Points
- Viruses are unique pathogens that utilize host metabolic machinery for reproduction.
- They exist as virions when extracellular and act as nucleic acids once intracellular.
- Viral shapes include helical, icosahedral, and complex.
- Their genomes can be either DNA or RNA, with RNA viruses having a higher mutation frequency.
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Description
Explore the fascinating world of viruses and bacteriophages in this quiz. Learn about their acellular structure, methods of infection, and impact on various organisms. Test your knowledge about these unique pathogens and their role in disease spread.
