Podcast
Questions and Answers
What is the defining characteristic of a retrovirus?
What is the defining characteristic of a retrovirus?
Which virus is an example of a positive-sense RNA virus?
Which virus is an example of a positive-sense RNA virus?
Viruses contain cytoplasm and a plasma membrane.
Viruses contain cytoplasm and a plasma membrane.
False
What are the two life cycles of a temperate bacteriophage?
What are the two life cycles of a temperate bacteriophage?
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What is the name of the protein sheath that surrounds the genetic material of a virus?
What is the name of the protein sheath that surrounds the genetic material of a virus?
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What type of genetic material does bacteriophage lambda contain?
What type of genetic material does bacteriophage lambda contain?
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Why can viruses evolve at a faster rate than other organisms?
Why can viruses evolve at a faster rate than other organisms?
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What is the term for when unrelated organisms independently evolve similar traits?
What is the term for when unrelated organisms independently evolve similar traits?
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All viruses acquire their envelope from the host cell's membrane.
All viruses acquire their envelope from the host cell's membrane.
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Which of the following is NOT a possible origin of viruses?
Which of the following is NOT a possible origin of viruses?
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What is the main difference between the lytic and lysogenic cycles of bacteriophage replication?
What is the main difference between the lytic and lysogenic cycles of bacteriophage replication?
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How do enveloped viruses acquire their envelope?
How do enveloped viruses acquire their envelope?
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What is the primary function of the enzyme reverse transcriptase?
What is the primary function of the enzyme reverse transcriptase?
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Why are viruses considered obligate intracellular parasites?
Why are viruses considered obligate intracellular parasites?
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Bacteriophage lambda is an example of an enveloped virus.
Bacteriophage lambda is an example of an enveloped virus.
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What are the two main methods by which viruses can access the host cell?
What are the two main methods by which viruses can access the host cell?
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Which of the following is an example of a non-retrovirus RNA virus?
Which of the following is an example of a non-retrovirus RNA virus?
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Viruses can directly replicate their DNA inside the host cell.
Viruses can directly replicate their DNA inside the host cell.
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What is the role of the integrase enzyme in retroviral replication?
What is the role of the integrase enzyme in retroviral replication?
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Study Notes
Viral Structure and Replication
- Viruses are small infectious agents, too small to see with a light microscope, requiring an electron microscope.
- Viral genetic material is either DNA or RNA.
- A protein capsid surrounds the genetic material.
- Viruses lack cytoplasm and a plasma membrane; therefore, they are obligate intracellular parasites.
RNA Viruses vs. Retroviruses
-
RNA viruses (non-retroviruses): Replicate by directly using RNA as the template for replication and protein synthesis.
- Some have positive-sense RNA (directly used as mRNA), others have negative-sense RNA (requiring conversion to positive-sense RNA).
- Examples: SARS-CoV-2 (positive-sense), influenza virus (negative-sense).
-
Retroviruses: Convert RNA to DNA using the enzyme reverse transcriptase.
- Their DNA is integrated into the host cell's genome.
- Example: HIV.
Viral Replication within Host Cells
- Lytic cycle: The virus takes over the host cell's machinery for rapid viral particle production. This ultimately leads to the host cell's lysis.
- Lysogenic cycle: The virus integrates its genome into the host cell's DNA (becoming a prophage) and replicates passively with the host genome. Later, the virus may excise its genome and enter the lytic cycle.
Viral Entry into Host Cells
- Some viruses enter host cells via endocytosis.
- Others fuse with the host cell membrane through receptor-mediated fusion.
Bacteriophage Lambda
- Infect bacteria, primarily E. coli.
- Have a double-stranded DNA genome and a protein capsid and tail.
- Temperate bacteriophages; can follow either a lytic or lysogenic cycle.
Viral Diversity and Envelopes
- Enveloped viruses: Have a lipid envelope derived from the host cell membrane, further protecting the viral genome and potentially helping with host cell entry and evasion of host immune systems.
- Non-enveloped viruses: Lack an envelope and consist solely of a capsid and genetic material.
Viral Origins and Evolution
- Scientists hypothesize potential origins from ancient RNA/DNA molecules, viroids, or transposons.
- Convergent evolution suggests viruses independently acquire similar characteristics to adapt to similar environments.
- Viral evolution is fast, driven by high mutation rates (common for RNA viruses because they lack efficient DNA-repair mechanisms), recombination, and rapid reproduction.
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Description
Test your knowledge on the structure and replication of viruses, including RNA viruses and retroviruses. This quiz will cover key concepts such as the lytic cycle and the differences between various types of viral replication. Perfect for students studying microbiology or virology.
