Questions and Answers
What is one main reason viruses are not considered living organisms?
Which structural component of a virus is responsible for genetic material protection?
What factor increases the susceptibility of enveloped viruses to external conditions?
What distinguishes bacteriophages from other viruses?
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What is the term for a complete virus particle that can infect a host cell?
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Which type of genetic material can viruses utilize?
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Why are non-enveloped viruses typically more resistant to sterilization methods?
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What viral structure assists in the recognition and attachment to the correct host cell?
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What defines the success of a bacteriophage in the lytic cycle?
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Which statement accurately describes the lysogenic cycle?
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What occurs when a provirus reverts to a lytic cycle?
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What distinguishes prions from other infectious agents?
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What is the primary mechanism by which viroids disrupt cellular function in plants?
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What is a consequence of bacteriophage infection on a bacterial host?
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How do prions affect proteins in an infected organism?
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Which of the following statements about HDV is correct?
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What is the primary role of RNA replicase in negative-sense RNA viruses?
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How does the integration of retroviral DNA into the host genome affect the host cell?
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Which enzyme is carried by retroviruses to convert RNA into DNA?
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What is a key feature of how enveloped viruses, like HIV, enter host cells?
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Which type of RNA virus can be directly translated into protein by host cell ribosomes?
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In which part of the cell do most DNA viruses need to be transcribed?
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What happens to a host cell during the lysis caused by viral replication?
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What allows some individuals to be immune to HIV infection?
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What is one effect of a virus fusing with the host cell membrane?
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What is viral progeny release through extrusion characterized by?
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Which statement best describes the role of structural proteins synthesized during viral replication?
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Which method is suggested to potentially deliver functional genes to treat diseases?
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What is the major implication of the fact that some viruses can only infect specific cells?
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What is the fate of the viral genome after replication in the host cell?
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Study Notes
Cell Theory and Viruses
- Viruses are acellular and do not meet the criteria for living organisms as per cell theory.
- Virus sizes range from 20 nm to 300 nm, while prokaryotes are 1–10 μm and eukaryotes are significantly larger.
Viral Structure
- Viruses consist of genetic material, a protein coat (capsid), and occasionally an envelope made of lipids.
- Genetic material can be circular or linear, and either single- or double-stranded DNA or RNA.
- Enveloped viruses are sensitive to heat and detergents, while non-enveloped viruses are more resistant and persist longer on surfaces.
- Viruses require a host cell for reproduction, acting as obligate intracellular parasites.
Bacteriophages
- Bacteriophages specifically infect bacteria by injecting their genetic material without entering the bacterium.
- They feature a tail sheath and tail fibers that facilitate binding and penetration of the bacterial cell.
Viral Genomes
- Viral genomes vary in size and can range from a few genes to several hundred.
- Positive-sense RNA viruses can be directly translated by host ribosomes, while negative-sense RNA viruses need a complementary RNA strand for translation.
- Retroviruses, such as HIV, carry reverse transcriptase to convert their RNA into DNA, integrating into the host genome for replication.
Gene Therapy
- Retroviruses and transduction techniques are researched for potential gene therapy applications to treat diseases caused by genetic anomalies.
Viral Life Cycle
- Viruses must bind to specific cell receptors to initiate infection.
- Entry methods include membrane fusion or endocytosis for enveloped viruses, while bacteriophages inject their genome through tail sheaths.
Translation and Progeny Assembly
- After entry, viral genetic material is translated into proteins using the host’s cellular machinery.
- DNA viruses typically enter the nucleus for transcription, while RNA viruses translate in the cytoplasm.
- Progeny virions are assembled from replicated genomes and structural proteins, with a single virus producing thousands of new virions.
Progeny Release Mechanisms
- Viral progeny can exit the host cell by:
- Cell death leading to viral spillover.
- Host cell lysis due to overwhelming virion numbers.
- Extrusion through plasma membrane fusion, allowing the host cell to survive.
Lytic and Lysogenic Cycles
- Bacteriophages can switch between lytic (virulent) and lysogenic cycles, with lysogeny involving integration into the host genome.
- Integrated viruses replicate alongside the bacteria during cell division, but can revert to lytic cycles under certain conditions, facilitating gene transfer (transduction) between bacteria.
Prions
- Prions are infectious proteins causing diseases through misfolding of normal proteins, resulting in cellular dysfunction.
- Associated diseases include bovine spongiform encephalopathy, Creutzfeldt–Jakob disease, and familial fatal insomnia.
Viroids
- Viroids consist of small circular single-stranded RNA and typically infect plants by silencing genes, disrupting protein synthesis.
- Some human-associated viroids, like hepatitis D virus (HDV), require co-infection with hepatitis B virus (HBV) to exert pathogenic effects.
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Description
This quiz focuses on the cell theory and the unique characteristics of viruses, covering their structure and classification as acellular entities. Learn about the differences between viruses, prokaryotes, and eukaryotes, including size and composition. Assess your understanding of how viruses operate and their role in biology.
