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Questions and Answers
What is the phenomenon called when a virus has a preference for infecting specific types of cells or tissues?
What is the phenomenon called when a virus has a preference for infecting specific types of cells or tissues?
Which stage involves the virus attaching to specific receptors on the host cell's plasma membrane?
Which stage involves the virus attaching to specific receptors on the host cell's plasma membrane?
Which of the following viruses is classified as a retrovirus?
Which of the following viruses is classified as a retrovirus?
What is the primary difference in mutation rates between RNA viruses and DNA viruses?
What is the primary difference in mutation rates between RNA viruses and DNA viruses?
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What method can the virus use to enter the host cell?
What method can the virus use to enter the host cell?
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What occurs during the eclipse period of viral replication?
What occurs during the eclipse period of viral replication?
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Which virus is known for causing chickenpox and shingles?
Which virus is known for causing chickenpox and shingles?
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Which of the following best describes the uncoating stage of the viral life cycle?
Which of the following best describes the uncoating stage of the viral life cycle?
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How long can the latent or eclipse period of a virus last?
How long can the latent or eclipse period of a virus last?
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Which virus is a common concern in dentistry due to its association with oral health issues?
Which virus is a common concern in dentistry due to its association with oral health issues?
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What is the main function of a virus's capsid?
What is the main function of a virus's capsid?
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What does viral tropism refer to?
What does viral tropism refer to?
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Which of the following statements about viruses is correct?
Which of the following statements about viruses is correct?
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What type of nucleic acid do viruses contain?
What type of nucleic acid do viruses contain?
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What is the role of the viral envelope?
What is the role of the viral envelope?
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Which type of symmetry does a filamentous virus exhibit?
Which type of symmetry does a filamentous virus exhibit?
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How do viruses replicate within a host?
How do viruses replicate within a host?
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What is the significance of viral persistence?
What is the significance of viral persistence?
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Which of the following is a correct classification based on viral nucleic acid?
Which of the following is a correct classification based on viral nucleic acid?
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What structural feature do prions lack that viruses possess?
What structural feature do prions lack that viruses possess?
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What occurs during the eclipse phase of a viral infection?
What occurs during the eclipse phase of a viral infection?
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What type of replication results in the death of the host cell?
What type of replication results in the death of the host cell?
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What is a characteristic of persistent viral infections?
What is a characteristic of persistent viral infections?
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During viral assembly, where can the assembly process occur?
During viral assembly, where can the assembly process occur?
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What are the two types of viral proteins synthesized during replication?
What are the two types of viral proteins synthesized during replication?
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What best describes viral latency?
What best describes viral latency?
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What role does mRNA play in the viral life cycle?
What role does mRNA play in the viral life cycle?
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What is the primary function of translocation in non-enveloped viruses?
What is the primary function of translocation in non-enveloped viruses?
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What type of viral infection allows the host cell to continue functioning normally?
What type of viral infection allows the host cell to continue functioning normally?
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What process occurs immediately after viral penetration into a host cell?
What process occurs immediately after viral penetration into a host cell?
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What characterizes a persistent viral infection compared to a latent infection?
What characterizes a persistent viral infection compared to a latent infection?
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What stage follows uncoating in the viral replication process?
What stage follows uncoating in the viral replication process?
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Which of the following diseases is caused by prions?
Which of the following diseases is caused by prions?
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Which of the following best describes tissue tropism?
Which of the following best describes tissue tropism?
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During which step are viral components assembled into new virus particles?
During which step are viral components assembled into new virus particles?
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What is a major difference between viruses and prions?
What is a major difference between viruses and prions?
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What happens to the host cell during the viral release stage if cell lysis occurs?
What happens to the host cell during the viral release stage if cell lysis occurs?
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What role does mRNA play in the viral life cycle?
What role does mRNA play in the viral life cycle?
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Which virus is primarily known for infecting birds and mammals?
Which virus is primarily known for infecting birds and mammals?
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What is a common characteristic of latent infections?
What is a common characteristic of latent infections?
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Which component of a virus is responsible for enclosing its genetic material?
Which component of a virus is responsible for enclosing its genetic material?
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What characteristic differentiates RNA viruses from DNA viruses in terms of genetic material?
What characteristic differentiates RNA viruses from DNA viruses in terms of genetic material?
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Which virus is known to affect immune cells and potentially lead to AIDS?
Which virus is known to affect immune cells and potentially lead to AIDS?
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Which type of virus is primarily associated with the risk of bloodborne transmission in dental settings?
Which type of virus is primarily associated with the risk of bloodborne transmission in dental settings?
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What feature of some viruses allows them to have an outer protective layer derived from the host cell?
What feature of some viruses allows them to have an outer protective layer derived from the host cell?
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Which viral symmetry is characterized by a long, thin shape?
Which viral symmetry is characterized by a long, thin shape?
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Which viral infection is significant in dental hygiene due to cold sores?
Which viral infection is significant in dental hygiene due to cold sores?
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Which classification of viruses includes those with double-stranded genomes?
Which classification of viruses includes those with double-stranded genomes?
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What is the significance of the capsomeres in virus structure?
What is the significance of the capsomeres in virus structure?
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What defines cellular tropism in the context of viral infections?
What defines cellular tropism in the context of viral infections?
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Study Notes
Virus Structure and Classification
- Viruses are infectious particles that reproduce by using a host cell's machinery.
- Composed of a DNA or RNA genome within a protein shell (capsid).
- Some have an external membrane envelope.
- Exhibit diverse shapes, genome types, and host ranges.
- Their size ranges from 10-100 nm (1/10 the size of bacteria).
- They are obligate intracellular parasites, requiring a living host cell for replication.
Virus Genome and Capsid
- Viruses possess either RNA or DNA genomes, never both.
- The capsid protects the genome and aids in host cell attachment.
- Some viruses have an envelope surrounding the capsid, often derived from the host cell membrane.
- Some viruses contain enzymes for replication.
Virus Symmetry and Nucleic Acid Classification
- Viruses are classified based on their symmetry (icosahedral, filamentous, head-tail) and nucleic acid type (dsDNA, ssDNA, dsRNA, ssRNA).
- RNA viruses generally show higher mutation rates than DNA viruses.
Dentally Relevant Viruses
- A table should be completed listing viruses and associated diseases (Picornavirus, Astrovirus, Calcivirus, Togavirus, Retrovirus, Orthomyxovirus, Paramyxovirus, Papillomavirus, Adenovirus, Coronavirus and their associated diseases).
- Key viruses relevant to dentistry include HIV, Hepatitis B, Varicella Zoster, Herpes, and Influenza viruses. Further details on these viruses are needed from the relevant workbook.
Viral Tropism and Replication
- Viral tropism refers to a virus's ability to infect specific cells, tissues, or host species.
- Viral replication involves several steps: adsorption (attachment to host cell receptors), penetration (entry into the cell), uncoating (release of the viral genome), transcription (mRNA synthesis), synthesis of viral components, assembly (formation of new virions), and release (from the host cell).
- Penetration mechanisms include endocytosis, fusion, and translocation. The uncoating/eclipse phase involves the release of the viral genome. Transcription utilizes the host cell's machinery. Viral proteins are structural or non-structural (enzymes). Assembly occurs in the nucleus, cytoplasm, or at the plasma membrane. Release can be lytic (host cell death) or lysogenic (host cell survival).
Viral Persistence and Latency
- Viral persistence describes a situation where the virus isn't cleared but remains in certain cells.
- Persistent infections can involve both active and dormant phases without causing rapid host cell death. (Examples are provided in the text: HIV, Epstein-Barr, Human Cytomegalovirus, Human Herpesviruses 6 and 7, Varicella-Zoster Virus, Human Papovaviruses and Hepatitis B Virus)
- Viral latency, a form of persistent infection, refers to a dormant state within a cell. It is distinct from chronic viral infections.
Virus Features
- Infectious particles: Viruses reproduce by using host cells.
- Genome: DNA or RNA, never both.
- Capsid: Protein shell enclosing the genome.
- Envelope: Some viruses have a lipid membrane from the host cell.
- Size: 10-100 nm, much smaller than bacteria.
- Obligate intracellular parasites: Replication only occurs within a living host cell.
Virus Structure
- Key components: Capsid (capsomeres), viral nucleic acid (DNA or RNA), envelope (in some), viral proteins (structural and non-structural).
- Nucleocapsid: Viral nucleic acid + capsid.
Virus Classification
- By symmetry: Icosahedral (20-sided, e.g., Herpes), filamentous (long, thin, e.g., Ebola), head-tail (e.g., bacteriophages).
- By nucleic acid type: DNA viruses (dsDNA or ssDNA); RNA viruses (dsRNA or ssRNA). RNA viruses generally mutate faster than DNA viruses.
Viruses and Disease
- HIV: Retrovirus infecting immune cells, leading to AIDS.
- HBV: DNA virus causing liver inflammation, potentially chronic disease or cancer.
- VZV: Herpesvirus causing chickenpox and shingles.
- HSV: Causes oral (HSV-1) and genital (HSV-2) herpes.
- Influenza virus: RNA virus causing seasonal flu; high mutation rate leads to new strains.
Viruses in Dentistry
- HSV: Causes cold sores; important for transmission.
- HPV: Linked to oral cancers.
- HBV and HCV: Bloodborne transmission risk in dental procedures.
- HIV: Compromises immune system, increasing risk of oral infections (e.g., oral candidiasis).
Viral Tropism
- Definition: A virus's ability to infect specific cell types, tissues, or species.
- Cellular tropism: Preference for specific cell types (e.g., HIV and CD4+ T cells).
- Tissue tropism: Preference for specific tissues (e.g., hepatitis viruses and liver cells).
- Host tropism: Ability to infect certain species (e.g., influenza and birds/mammals).
Viral Replication and Dissemination
- Steps: Adsorption (attachment), penetration (endocytosis, fusion, translocation), uncoating, transcription (mRNA synthesis), synthesis of viral components, assembly, release (cell lysis or budding).
Viral Persistence and Latency
- Viral persistence: Virus remains in cells; examples include HIV, EBV, and Hepatitis B.
- Viral latency: Virus is dormant but can reactivate later (e.g., HSV, VZV). Latency is a type of persistent infection.
Prions
- Definition: Infectious proteins causing degenerative brain diseases (e.g., CJD, mad cow disease).
- Key difference from viruses: Lack nucleic acids; resistant to standard disinfection.
Summary of Viral Information
- Viruses are small, infectious agents requiring host cells for replication.
- Structure: Capsid, nucleic acid (DNA or RNA), sometimes an envelope.
- Important dental viruses: HSV, HPV, HBV, HCV, HIV.
- Understanding viral replication, tropism, and latency is crucial for managing infections.
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Description
Test your knowledge on the structure and classification of viruses. Explore the concepts of virus genomes, capsids, and their various shapes and host ranges. This quiz covers essential details about virus symmetry and nucleic acid classification.
