Podcast
Questions and Answers
Which of the following statements best describes why viruses are not considered true living organisms?
Which of the following statements best describes why viruses are not considered true living organisms?
What characteristic do viruses exhibit that is similar to living organisms?
What characteristic do viruses exhibit that is similar to living organisms?
Which feature is NOT associated with viruses?
Which feature is NOT associated with viruses?
In what way do viruses depend on host cells?
In what way do viruses depend on host cells?
Signup and view all the answers
Which of the following is a true statement about viruses?
Which of the following is a true statement about viruses?
Signup and view all the answers
What is the highest taxon level used for many viruses?
What is the highest taxon level used for many viruses?
Signup and view all the answers
Which suffix is used for virus family names?
Which suffix is used for virus family names?
Signup and view all the answers
Which of the following is true about binomial nomenclature in relation to viruses?
Which of the following is true about binomial nomenclature in relation to viruses?
Signup and view all the answers
What is true about virus genus names?
What is true about virus genus names?
Signup and view all the answers
Which of these examples correctly follows the naming convention for viruses?
Which of these examples correctly follows the naming convention for viruses?
Signup and view all the answers
What determines the host range of a virus?
What determines the host range of a virus?
Signup and view all the answers
Which of the following hosts is protected from the influenza virus?
Which of the following hosts is protected from the influenza virus?
Signup and view all the answers
Which type of virus specifically infects fungi?
Which type of virus specifically infects fungi?
Signup and view all the answers
What can contribute to species resistance against certain viruses?
What can contribute to species resistance against certain viruses?
Signup and view all the answers
Which of the following statements is true regarding the infection of animals by measles virus?
Which of the following statements is true regarding the infection of animals by measles virus?
Signup and view all the answers
What is the typical size range of viruses?
What is the typical size range of viruses?
Signup and view all the answers
Which of the following describes helical viruses?
Which of the following describes helical viruses?
Signup and view all the answers
Which structure is typical of complex (binal) viruses?
Which structure is typical of complex (binal) viruses?
Signup and view all the answers
Enveloped viruses differ from helical and polyhedral viruses in that they are:
Enveloped viruses differ from helical and polyhedral viruses in that they are:
Signup and view all the answers
Which of the following correctly identifies a characteristic of polyhedral viruses?
Which of the following correctly identifies a characteristic of polyhedral viruses?
Signup and view all the answers
What is the term used to describe the combination of a virus's capsid and genome?
What is the term used to describe the combination of a virus's capsid and genome?
Signup and view all the answers
Which of the following statements correctly describes the role of spikes in viruses?
Which of the following statements correctly describes the role of spikes in viruses?
Signup and view all the answers
What distinguishes an enveloped virus from a naked virus?
What distinguishes an enveloped virus from a naked virus?
Signup and view all the answers
Which type of nucleic acid can be found in viral genomes?
Which type of nucleic acid can be found in viral genomes?
Signup and view all the answers
Which protein subunits make up the viral capsid?
Which protein subunits make up the viral capsid?
Signup and view all the answers
What is the purpose of a plaque assay method?
What is the purpose of a plaque assay method?
Signup and view all the answers
What do plaques represent in a lawn of bacteria during a plaque assay?
What do plaques represent in a lawn of bacteria during a plaque assay?
Signup and view all the answers
What does the term 'plaque-forming unit' (PFU) refer to?
What does the term 'plaque-forming unit' (PFU) refer to?
Signup and view all the answers
In a plaque assay, what is visualized in the agar?
In a plaque assay, what is visualized in the agar?
Signup and view all the answers
Which of the following best describes a plaque in the context of bacteriophages?
Which of the following best describes a plaque in the context of bacteriophages?
Signup and view all the answers
What is a requirement for viruses to grow?
What is a requirement for viruses to grow?
Signup and view all the answers
Which method is NOT used for culturing animal viruses?
Which method is NOT used for culturing animal viruses?
Signup and view all the answers
What indicates successful viral growth when using embryonated eggs for culturing?
What indicates successful viral growth when using embryonated eggs for culturing?
Signup and view all the answers
Which of the following practices does NOT involve the direct use of living cells?
Which of the following practices does NOT involve the direct use of living cells?
Signup and view all the answers
Which culturing method relies on direct observation of an embryo's response to viral infection?
Which culturing method relies on direct observation of an embryo's response to viral infection?
Signup and view all the answers
What characteristic is typical of most bacteria compared to obligate intracellular parasites like Rickettsias?
What characteristic is typical of most bacteria compared to obligate intracellular parasites like Rickettsias?
Signup and view all the answers
Which statement accurately describes Rickettsias?
Which statement accurately describes Rickettsias?
Signup and view all the answers
What is a significant difference between free-living bacteria and Rickettsias?
What is a significant difference between free-living bacteria and Rickettsias?
Signup and view all the answers
Which of the following best describes the survival requirements of most bacteria?
Which of the following best describes the survival requirements of most bacteria?
Signup and view all the answers
Which statement is NOT true about obligate intracellular parasites like Rickettsias?
Which statement is NOT true about obligate intracellular parasites like Rickettsias?
Signup and view all the answers
What is the primary role of interferon (IFN) in response to viral infection?
What is the primary role of interferon (IFN) in response to viral infection?
Signup and view all the answers
How does interferon (IFN) signal neighboring cells during a viral infection?
How does interferon (IFN) signal neighboring cells during a viral infection?
Signup and view all the answers
What action does interferon (IFN) induce specifically in virus-infected cells?
What action does interferon (IFN) induce specifically in virus-infected cells?
Signup and view all the answers
Which of the following statements about interferon (IFN) is correct?
Which of the following statements about interferon (IFN) is correct?
Signup and view all the answers
What effect does interferon (IFN) have on healthy cells during a viral response?
What effect does interferon (IFN) have on healthy cells during a viral response?
Signup and view all the answers
What does the term 'cytopathic effects' (CPE) refer to in the context of viral infections?
What does the term 'cytopathic effects' (CPE) refer to in the context of viral infections?
Signup and view all the answers
Which testing method is primarily used for the direct detection of viral genomic material?
Which testing method is primarily used for the direct detection of viral genomic material?
Signup and view all the answers
Which of the following is NOT a characteristic of serological tests for virus detection?
Which of the following is NOT a characteristic of serological tests for virus detection?
Signup and view all the answers
What is a key advantage of using cytopathic effect observations in viral testing?
What is a key advantage of using cytopathic effect observations in viral testing?
Signup and view all the answers
In what scenario would PCR tests be preferred over serological tests?
In what scenario would PCR tests be preferred over serological tests?
Signup and view all the answers
What occurs during the biosynthesis phase of the lytic cycle in bacterial viral infections?
What occurs during the biosynthesis phase of the lytic cycle in bacterial viral infections?
Signup and view all the answers
In the lysogenic cycle, what term describes viral DNA that is incorporated into the host genome?
In the lysogenic cycle, what term describes viral DNA that is incorporated into the host genome?
Signup and view all the answers
Which of the following statements about the lysogenic cycle is true?
Which of the following statements about the lysogenic cycle is true?
Signup and view all the answers
What is an evolutionary advantage of a virus's ability to enter either the lytic or lysogenic cycle?
What is an evolutionary advantage of a virus's ability to enter either the lytic or lysogenic cycle?
Signup and view all the answers
Which of the following best describes the role of integrase in the lysogenic cycle?
Which of the following best describes the role of integrase in the lysogenic cycle?
Signup and view all the answers
What happens to the varicella-zoster virus after a person recovers from chickenpox?
What happens to the varicella-zoster virus after a person recovers from chickenpox?
Signup and view all the answers
Which of the following describes how shingles differs from chickenpox?
Which of the following describes how shingles differs from chickenpox?
Signup and view all the answers
During latency, the varicella-zoster virus does which of the following?
During latency, the varicella-zoster virus does which of the following?
Signup and view all the answers
What is not a characteristic of the varicella-zoster virus during its latent phase?
What is not a characteristic of the varicella-zoster virus during its latent phase?
Signup and view all the answers
What triggers the reactivation of the varicella-zoster virus to cause shingles?
What triggers the reactivation of the varicella-zoster virus to cause shingles?
Signup and view all the answers
What characterizes the rash caused by chickenpox?
What characterizes the rash caused by chickenpox?
Signup and view all the answers
What occurs during the latent period of a viral infection?
What occurs during the latent period of a viral infection?
Signup and view all the answers
Which phase of a viral infection is characterized by the absence of complete virion particles inside the infected cell?
Which phase of a viral infection is characterized by the absence of complete virion particles inside the infected cell?
Signup and view all the answers
What is the primary consequence of viral release from an infected cell?
What is the primary consequence of viral release from an infected cell?
Signup and view all the answers
What distinguishes acute infections from latent infections?
What distinguishes acute infections from latent infections?
Signup and view all the answers
Which term best describes the new complete viruses produced during a viral infection?
Which term best describes the new complete viruses produced during a viral infection?
Signup and view all the answers
What is the primary purpose of transduction in molecular biology?
What is the primary purpose of transduction in molecular biology?
Signup and view all the answers
How does transduction facilitate horizontal gene transfer in bacteria?
How does transduction facilitate horizontal gene transfer in bacteria?
Signup and view all the answers
What occurs during the excision process in transduction?
What occurs during the excision process in transduction?
Signup and view all the answers
Which statement accurately describes the viral DNA after lysogeny?
Which statement accurately describes the viral DNA after lysogeny?
Signup and view all the answers
What is the outcome of a bacteriophage excising itself from a host chromosome?
What is the outcome of a bacteriophage excising itself from a host chromosome?
Signup and view all the answers
What is a characteristic feature of a transformed cell?
What is a characteristic feature of a transformed cell?
Signup and view all the answers
How do oncogenic viruses contribute to the onset of cancer?
How do oncogenic viruses contribute to the onset of cancer?
Signup and view all the answers
What percentage of all human cancers worldwide are estimated to be linked to oncogenic viruses?
What percentage of all human cancers worldwide are estimated to be linked to oncogenic viruses?
Signup and view all the answers
Which of the following best describes the effect of oncogenes on normal cells?
Which of the following best describes the effect of oncogenes on normal cells?
Signup and view all the answers
What is one manifestation of tumor-specific antigens in transformed cells?
What is one manifestation of tumor-specific antigens in transformed cells?
Signup and view all the answers
Study Notes
Viral Characteristics
- Viruses are infectious agents, obligate intracellular parasites.
- They infect various organisms, including animals, plants, fungi, and bacteria. Some viruses, like bacteriophages, infect only bacteria, while others infect fungi (mycophages). Animal viruses affect only animals, and plant viruses infect only plants.
- Viruses are not considered living organisms.
- Viruses lack a cell membrane, cytoplasm, and cellular organelles.
- They cannot perform metabolism independently; they rely on host cell enzymes and metabolic processes.
- Viruses cannot replicate independently.
- Viral classification does not utilize the full taxonomic hierarchy (Kingdom, Phylum, Class, Order, Family, Genus, Species) found in other organisms.
- Viruses are typically much smaller than bacteria, generally ranging from 5 to 300 nanometers in size.
- Most bacteria are free-living, meaning they can survive and reproduce outside a host cell.
- Rickettsias are bacteria that are obligate intracellular parasites, meaning they must live inside the cells of another organism to survive.
Viral Structure
- Genome: The viral genome is the entire genetic information of a virus, and it can be either circular or linear.. It can be single-stranded or double-stranded DNA or RNA.
- Capsid: A protein shell surrounding the genome.
- Capsomeres: Protein subunits that compose the capsid.
- Nucleocapsid: The capsid plus the genome.
-
Envelope: Some viruses have an outer membrane envelope.
- Naked/Nonenveloped Viruses: Do not have an envelope.
- Enveloped Viruses: The envelope originates from the host cell membrane.
-
Spikes: Viral glycoproteins projecting from the envelope or capsid.
- Function in attaching the virus to receptors on host cells.
- Present in both enveloped and nonenveloped viruses.
- Example: H and N spikes on influenza viruses (e.g., H1N1, H2N2 influenza viruses).
Viral Shapes
- Helical Viruses: Nucleic acid is enclosed within a hollow, helical protein cylinder.
- Polyhedral Viruses: Nucleic acid is surrounded by a polyhedral (many-sided) protein shell, often in the form of an icosahedron.
- Enveloped Viruses: Nucleic acid is surrounded by a helical or polyhedral core and further covered by an envelope.
- Complex (Binal) Viruses: Possess a head and tail structure.
Viral Life-like Characteristics
- Viruses possess a nucleic acid genome.
- They exhibit evolution through mutations.
- Viruses replicate inside living host cells, utilizing host cell machinery.
Viral Taxonomy and Nomenclature
- Taxonomy is the study of classification; each level of classification is called a taxon.
- The binomial nomenclature system uses a two-part name (genus and species) to identify organisms.
- Examples include Escherichia coli and Bacillus subtilis.
- Binomial nomenclature is not used for naming viruses.
- For viral classification, "order" is often the highest level used.
- Virus family names end in "-viridae" (e.g., Coronaviridae, Orthomyxoviridae).
- Virus genus names end in "-virus" (e.g., Coronavirus, Influenza virus).
Host Range
- Most viruses infect specific hosts.
- Host range is determined by specific host receptors and cellular factors.
- Absence of specific viral receptors protects hosts and contributes to species resistance. For example, plants, fungi lack receptors for influenza viruses, making them resistant to this virus. Similarly, dogs lack receptors for measles virus.
Plaque Assay Method
- Used for culturing bacteriophages.
- Bacteriophages form plaques, which are circular clearings on a lawn of bacteria on the surface of agar. Each plaque is filled with virus.
- Plaque-forming unit (PFU): a measure of the number of infectious virus particles.
Culturing Viruses
- Viruses are obligate intracellular parasites, meaning they cannot grow in a host-free medium.
-
Culturing Animal Viruses:
- Live animals: One method of culturing animal viruses.
- Embryonated eggs: Viruses can be cultured in embryonated eggs by injecting the virus into the egg and observing changes or death of the embryo.
- Animal cell cultures: Another method involving growing animal cells in a laboratory setting to culture viruses.
Interferon (IFN)
- Interferon (IFN) is a protein signaling molecule, a cytokine or hormone.
- Virus-infected cells release IFN, alerting neighboring cells via paracrine signaling.
- Paracrine signaling prompts healthy cells and immune cells to enter a viral protective mode.
- IFN also targets virus-infected cells, inducing apoptosis (programmed cell death).
Testing for the Presence of Virus
- Viral Infection - Cytopathic Effects (CPE): Changes in host cells due to viral infection, like cell lysis, can be observed under a microscope. Healthy cells vs CPE allows identification.
- Serological Tests: Antibody-based tests used to detect the presence of specific viral antigens or antibodies in a sample, such as serum.
- PCR (Polymerase Chain Reaction): A molecular technique to amplify and detect specific viral genetic material (DNA or RNA) in a sample. This is a sensitive method that can detect even low amounts of viral DNA or RNA.
Latent Infections
- Some viruses can undergo a latent infection.
- The virus initially causes an acute infection.
- Then it becomes dormant (remains hidden inside the cell).
- For example, Varicella-zoster virus causes chickenpox. Following recovery, the virus remains dormant in nerve cells.
- Years later, it can reactivate and cause shingles.
- Shingles affects nerve cells; chickenpox affects many areas.
Viral Replication - Lytic and Lysogenic Cycles
-
Bacteriophage Lytic Cycle:
- Penetration: Only phage DNA enters the host cell, not the entire virus.
- Biosynthesis: Host cell machinery is used to manufacture viral components (DNA, capsid).
- Lysis: Host cell breaks up and dies, releasing new viruses.
- Animal Virus Lytic Cycle: (Details on animal viral lytic replication would be needed here for this section to be complete.)
-
Lysogenic Cycle:
- Prophage/Provirus: Viral DNA integrates into the host cell's genome using viral enzyme integrase.
- Lysogenic cycle: Does not result in immediate host cell lysis.
- Prophage formation: Occurs in both bacterial and animal cells.
- Excision from host chromosome: Prophage can exit the host genome and enter the lytic cycle.
- Evolutionary Advantage: The ability to switch between lytic and lysogenic cycles provides an evolutionary benefit for the virus.
Transduction
- Transduction: A technique used by molecular biologists to introduce new genes into cells.
- Transduction in bacteria occurs naturally.
- Bacteriophages introduce genes from one bacterium to another, facilitating horizontal gene transfer.
-
Transduction Process:
- Following viral infection and lysogeny, viral DNA is incorporated into the host chromosome.
- Later, the prophage (viral DNA) excises itself from the host chromosome.
- The excision process is often imprecise and may include excision of host genes as well.
- The new virus can now introduce new host genes to other species.
Additional Information from Provided Text
- Latent period: The interval from infection/entry to virion formation.
- Virions: New complete viruses.
- Eclipse period: No complete virion particles are present inside the infected cell.
- Viral Release: Results in an increase of extracellular virus; patients exhibit symptoms.
Transformation of Normal Cells into Tumor Cells
- Viral Oncogenes: Oncogenic viruses can cause cancer by disrupting normal cell growth control mechanisms, leading to uncontrolled cell proliferation and tumor formation.
- Oncogenes become integrated into the host cell’s DNA and transform normal cells into cancerous cells. Approximately 15% of human cancers worldwide are linked to oncogenic viruses.
-
Transformed Cell Characteristics:
- Increased cell division
- Loss of contact inhibition
- Presence of tumor-specific antigen on cell surface and nucleus.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Description
Test your knowledge about viruses and their unique characteristics. This quiz covers viral structure, life cycles, and their role as infectious agents. Understand the differences between viruses and living organisms.
