Podcast
Questions and Answers
During the lytic cycle, at which stage does the phage inject its DNA into the bacterial cell?
During the lytic cycle, at which stage does the phage inject its DNA into the bacterial cell?
Which of the following is a characteristic of lysogenic phages?
Which of the following is a characteristic of lysogenic phages?
What is a prophage?
What is a prophage?
A lysogenic cell is immune to reinfection by the same phage. What is the most likely reason for this immunity?
A lysogenic cell is immune to reinfection by the same phage. What is the most likely reason for this immunity?
Signup and view all the answers
What is phage conversion?
What is phage conversion?
Signup and view all the answers
In specialized transduction, how are bacterial genes transferred from one bacterium to another?
In specialized transduction, how are bacterial genes transferred from one bacterium to another?
Signup and view all the answers
During the excision of a prophage from the bacterial chromosome, an error occurs, leading to the inclusion of some adjacent bacterial genes within the excised phage DNA. This recombinant phage infects a new bacterial cell. Which of the following outcomes is LEAST likely?
During the excision of a prophage from the bacterial chromosome, an error occurs, leading to the inclusion of some adjacent bacterial genes within the excised phage DNA. This recombinant phage infects a new bacterial cell. Which of the following outcomes is LEAST likely?
Signup and view all the answers
What specific risk is associated with live viral vaccines, as exemplified by the polio vaccine?
What specific risk is associated with live viral vaccines, as exemplified by the polio vaccine?
Signup and view all the answers
Individuals with anaphylactic reactions to eggs should not be given vaccines grown in chick embryos. Which vaccines should be avoided in these individuals?
Individuals with anaphylactic reactions to eggs should not be given vaccines grown in chick embryos. Which vaccines should be avoided in these individuals?
Signup and view all the answers
A traveler is planning a trip to an area where Yellow Fever is endemic. Based on the information, which type of vaccine would be MOST suitable for them?
A traveler is planning a trip to an area where Yellow Fever is endemic. Based on the information, which type of vaccine would be MOST suitable for them?
Signup and view all the answers
Which characteristic distinguishes killed viral vaccines from live viral vaccines?
Which characteristic distinguishes killed viral vaccines from live viral vaccines?
Signup and view all the answers
A researcher is investigating novel strategies to enhance vaccine efficacy. Considering the properties of different vaccine types, which approach would MOST likely lead to a long-lasting immunity and strong cell-mediated response, while also posing the GREATEST risk of complications in immunocompromised individuals?
A researcher is investigating novel strategies to enhance vaccine efficacy. Considering the properties of different vaccine types, which approach would MOST likely lead to a long-lasting immunity and strong cell-mediated response, while also posing the GREATEST risk of complications in immunocompromised individuals?
Signup and view all the answers
What is the primary mechanism by which APOBEC3G reduces HIV infectivity?
What is the primary mechanism by which APOBEC3G reduces HIV infectivity?
Signup and view all the answers
How does HIV counteract the antiviral effects of APOBEC3G?
How does HIV counteract the antiviral effects of APOBEC3G?
Signup and view all the answers
Which of the following is NOT a mechanism by which fever can inhibit viral infections?
Which of the following is NOT a mechanism by which fever can inhibit viral infections?
Signup and view all the answers
How do antibodies neutralize viruses?
How do antibodies neutralize viruses?
Signup and view all the answers
What is the role of perforins in T-lymphocyte-mediated lysis of virus-infected cells?
What is the role of perforins in T-lymphocyte-mediated lysis of virus-infected cells?
Signup and view all the answers
Which factor would most likely lead to decreased Ig production and phagocytosis?
Which factor would most likely lead to decreased Ig production and phagocytosis?
Signup and view all the answers
What is the primary difference between active and passive immunity?
What is the primary difference between active and passive immunity?
Signup and view all the answers
Which of the following mechanisms do cytotoxic T cells employ to eliminate virus-infected cells, representing a combined effect of direct cellular damage and programmed cell death?
Which of the following mechanisms do cytotoxic T cells employ to eliminate virus-infected cells, representing a combined effect of direct cellular damage and programmed cell death?
Signup and view all the answers
Consider a scenario where an individual with a genetic anomaly lacks the ability to produce Vif (viral infectivity factor). Assuming this individual is exposed to HIV-1, how would the interplay between APOBEC3G and the mutated virus likely manifest?
Consider a scenario where an individual with a genetic anomaly lacks the ability to produce Vif (viral infectivity factor). Assuming this individual is exposed to HIV-1, how would the interplay between APOBEC3G and the mutated virus likely manifest?
Signup and view all the answers
What characteristic defines cell cultures used for virus isolation?
What characteristic defines cell cultures used for virus isolation?
Signup and view all the answers
What is the defining characteristic of primary cell lines?
What is the defining characteristic of primary cell lines?
Signup and view all the answers
What is the typical lifespan of diploid cell lines in terms of subcultures?
What is the typical lifespan of diploid cell lines in terms of subcultures?
Signup and view all the answers
Which of the following is a technique used in virus isolation to enhance viral detection?
Which of the following is a technique used in virus isolation to enhance viral detection?
Signup and view all the answers
What cytopathic effect (CPE) is observed when cells are sensitive to the effects of viruses?
What cytopathic effect (CPE) is observed when cells are sensitive to the effects of viruses?
Signup and view all the answers
Which of the following is an example of a diploid cell line?
Which of the following is an example of a diploid cell line?
Signup and view all the answers
During the preparation of primary cell cultures, what is the role of proteolytic enzymes?
During the preparation of primary cell cultures, what is the role of proteolytic enzymes?
Signup and view all the answers
Which cell culture method is considered the gold standard for viral identification?
Which cell culture method is considered the gold standard for viral identification?
Signup and view all the answers
A researcher observes that a cell culture has undergone significant morphological changes, including cell lysis and syncytia formation, following inoculation with a clinical sample. This is indicative of what phenomenon?
A researcher observes that a cell culture has undergone significant morphological changes, including cell lysis and syncytia formation, following inoculation with a clinical sample. This is indicative of what phenomenon?
Signup and view all the answers
A lab technician is tasked with establishing a primary cell culture from a tissue biopsy. After enzymatic digestion and seeding the cells into a culture flask, they observe very slow growth and eventual senescence after only a few passages, despite optimal culture conditions. What is the most likely reason for this outcome?
A lab technician is tasked with establishing a primary cell culture from a tissue biopsy. After enzymatic digestion and seeding the cells into a culture flask, they observe very slow growth and eventual senescence after only a few passages, despite optimal culture conditions. What is the most likely reason for this outcome?
Signup and view all the answers
When viral isolation in cell cultures is not possible, which method is most useful for determining past infection?
When viral isolation in cell cultures is not possible, which method is most useful for determining past infection?
Signup and view all the answers
IgM antibodies typically appear within what timeframe following a primary viral infection?
IgM antibodies typically appear within what timeframe following a primary viral infection?
Signup and view all the answers
What is the primary reason antibody detection is not useful for diagnosing chronic viral infections like HIV?
What is the primary reason antibody detection is not useful for diagnosing chronic viral infections like HIV?
Signup and view all the answers
In serological testing, what does a four-fold increase in antibody titer between acute and convalescent phase serum samples typically indicate?
In serological testing, what does a four-fold increase in antibody titer between acute and convalescent phase serum samples typically indicate?
Signup and view all the answers
What is the main advantage of a killed virus vaccine compared to a live, attenuated vaccine?
What is the main advantage of a killed virus vaccine compared to a live, attenuated vaccine?
Signup and view all the answers
Which type of vaccine typically stimulates both IgA and IgG antibody production when administered via the natural route?
Which type of vaccine typically stimulates both IgA and IgG antibody production when administered via the natural route?
Signup and view all the answers
A vaccine that contains only purified protein subunits from a virus will primarily stimulate which type of immune response?
A vaccine that contains only purified protein subunits from a virus will primarily stimulate which type of immune response?
Signup and view all the answers
Why do killed virus vaccines typically require booster shots compared to live attenuated vaccines?
Why do killed virus vaccines typically require booster shots compared to live attenuated vaccines?
Signup and view all the answers
A researcher is developing a new vaccine against a highly mutable virus. Which vaccine approach would likely offer the broadest and most durable protection, considering the need to stimulate both humoral and cell-mediated immunity?
A researcher is developing a new vaccine against a highly mutable virus. Which vaccine approach would likely offer the broadest and most durable protection, considering the need to stimulate both humoral and cell-mediated immunity?
Signup and view all the answers
A patient who received a vaccine 10 years ago is exposed anew to the virus. It turns out the vaccine was a killed virus vaccine. The patient is displaying very mild symptoms. What immunological parameter is most likely responsible for this mild presentation, compared to an unvaccinated individual?
A patient who received a vaccine 10 years ago is exposed anew to the virus. It turns out the vaccine was a killed virus vaccine. The patient is displaying very mild symptoms. What immunological parameter is most likely responsible for this mild presentation, compared to an unvaccinated individual?
Signup and view all the answers
Flashcards
Lytic Cycle
Lytic Cycle
A viral replication cycle resulting in the destruction of the host cell.
Step 1: Attachment
Step 1: Attachment
The phage attaches to receptor on the bacterial cell surface.
Step 2: Penetration
Step 2: Penetration
The phage injects its DNA into the bacterial cell, leaving the capsid outside.
Step 3: Biosynthesis
Step 3: Biosynthesis
Signup and view all the flashcards
Lysogenic Cycle
Lysogenic Cycle
Signup and view all the flashcards
Prophage
Prophage
Signup and view all the flashcards
Phage Conversion
Phage Conversion
Signup and view all the flashcards
CXCR4 Receptor Interference
CXCR4 Receptor Interference
Signup and view all the flashcards
APOBEC3G
APOBEC3G
Signup and view all the flashcards
Vif Protein
Vif Protein
Signup and view all the flashcards
Fever
Fever
Signup and view all the flashcards
Mucociliary Clearance
Mucociliary Clearance
Signup and view all the flashcards
Factors Modifying Host Defenses
Factors Modifying Host Defenses
Signup and view all the flashcards
Active Immunity
Active Immunity
Signup and view all the flashcards
Neutralization
Neutralization
Signup and view all the flashcards
Passive Immunity
Passive Immunity
Signup and view all the flashcards
Live Viral Vaccine
Live Viral Vaccine
Signup and view all the flashcards
Killed Viral Vaccine
Killed Viral Vaccine
Signup and view all the flashcards
Duration of Immunity
Duration of Immunity
Signup and view all the flashcards
Immunoglobulin Produced
Immunoglobulin Produced
Signup and view all the flashcards
Cell Culture
Cell Culture
Signup and view all the flashcards
Cell Monolayer
Cell Monolayer
Signup and view all the flashcards
Cell Line
Cell Line
Signup and view all the flashcards
Cytopathic Effects (CPE)
Cytopathic Effects (CPE)
Signup and view all the flashcards
Primary Cell Cultures
Primary Cell Cultures
Signup and view all the flashcards
Diploid Cell Lines
Diploid Cell Lines
Signup and view all the flashcards
Diploid Cell Examples
Diploid Cell Examples
Signup and view all the flashcards
Heteroploid Cell Lines
Heteroploid Cell Lines
Signup and view all the flashcards
SVCE Cultures
SVCE Cultures
Signup and view all the flashcards
Multiwell Microplate Cultures
Multiwell Microplate Cultures
Signup and view all the flashcards
Serological Detection
Serological Detection
Signup and view all the flashcards
IgM Antibodies
IgM Antibodies
Signup and view all the flashcards
IgG Antibodies
IgG Antibodies
Signup and view all the flashcards
Paired Sera
Paired Sera
Signup and view all the flashcards
Four-fold Increase titer
Four-fold Increase titer
Signup and view all the flashcards
False Positive Reaction
False Positive Reaction
Signup and view all the flashcards
False Negative Reaction
False Negative Reaction
Signup and view all the flashcards
Live Attenuated Vaccine
Live Attenuated Vaccine
Signup and view all the flashcards
Study Notes
Virology Overview
- Virology is the study of viruses
- Viruses are not cells; they are nucleic acid molecules that invade cells and replicate within them.
- Viruses have no metabolic processes of their own.
- Viruses are classified as functionally active or inactive, rather than alive or dead.
- Outside a host cell, a virus particle is called a virion and is metabolically inert.
- Viruses lack the majority of enzymes for metabolism (lacking CHON synthesis and ATP generation)
Nature of Viruses
- Viruses are a heterogeneous class of agents varying in size, morphology, complexity, and host range.
- Viruses have a genome (either RNA or DNA, not both) surrounded by a protective protein shell.
- Viruses multiply only in living cells and are dependent on the host's energy-yielding and CHON-synthesizing apparatus.
- Viruses are obligate intracellular parasites.
- Viral genome separation from their protective shell is an initial step of the multiplication cycle.
- A single virus particle can replicate to produce hundreds of progeny viruses while a one cell division creates only two daughter cells.
Viruses vs. Bacteria
| Feature | Bacteria | Rickettsias/Chlamydias | Viruses |
|---|---|---|---|
| Intracellular parasite | No | Yes | Yes |
| Plasma membrane | Yes | Yes | No |
| Binary fission | Yes | No/Yes | No |
| Pass through bacteriological filters | No | No/Yes | Yes |
| Possess both DNA and RNA | Yes | Yes/No | No |
| ATP-generating metabolism | Yes | Yes/No | No |
| Ribosomes | Yes | Yes | No |
| Sensitive to antibiotics | Yes | Yes | No |
| Sensitive to interferon | No | No | Yes |
Viruses vs. Cells
| Property | Virus | Cell |
|---|---|---|
| Type of nucleic acid | DNA or RNA | DNA |
| Proteins | Yes | Yes |
| Lipoprotein membrane | May have | Yes |
| Ribosomes | No | Yes |
| Mitochondria | No | Yes |
| Enzymes | Few, if any | Many |
| Replication | No, uses host cell | Yes (binary fission or mitosis) |
Host Range of Viruses
- Viruses have a spectrum of host cells they can infect (e.g., invertebrates, vertebrates, plants, protists, fungi, bacteria)
- Most viruses infect specific cell types of a single host species.
- Host range is determined by the virus's requirements for specific attachment sites on the host cell (e.g., receptors).
- Examples determining host range are seen in bacteria (cell wall, fimbriae, flagella) and animals (plasma membrane).
Viral Size
- Viruses range in size from 20 to 1000 nm in length.
- Electron microscopy is used to determine viral size.
Viral Structure Components
- Viral nucleic acids (DNA or RNA)
- Viral proteins (capsid)
- Viral capsid
- Viral envelope
Viral Nucleic Acids
- Viruses can have either DNA or RNA, but not both.
- Viral genomes can be single-stranded (ss) or double-stranded (ds)
- Almost all viruses have a single copy of their genome (haploid) except retroviruses (diploid/dimer)
- Viral genomes can be linear, circular, or segmented (only for RNA)
- Viral genomes vary in size from a few thousand to 250,000 nucleotides.
- Viral genomes encode enzymes and structural proteins.
Viral Classification by Nucleic Acid Type
- DNA viruses: characterized as "HAPPY"
- RNA viruses:
- Positive (+) stranded RNA
- Negative (-) stranded RNA
- Double-stranded RNA
- Retroviruses
Viral Classification by RNA Viruses mRNA Synthesis Strategy
- Positive (+) stranded RNA: uses their RNA genome directly as mRNA, which is translated in host ribosomes to proteins
- Negative (-) stranded RNA: must first be transcribed into positive stranded RNA by an enzyme in their capsid (RNA-dependent RNA polymerase) to begin translation.
- Double-stranded RNA: carry their own RNA polymerase
- Retroviruses: have negative-polarity single-stranded RNA genomes, but are transcribed into dsDNA by reverse transcriptase enzyme, which is carried by the virus.
Viral Capsid/Envelope
- The capsid protects the virus’s nucleic acid.
- Capsid is made of protein subunits called capsomeres.
- Nucleocapsid is a structure referring to the nucleic acid and capsid.
- Some viruses have an envelope (a lipid bilayer) that surrounds the capsid.
- Envelope spikes/glycoproteins are crucial for attachment to host cells.
- Naked/non-enveloped viruses lack an envelope and are only surrounded by a capsid.
Capsid Morphology
- Enveloped helical
- Naked icosahedral/naked polyhedral
- Enveloped icosahedral/enveloped polyhedral
- Complex viruses
Helical Viruses
- Resemble long rods (rigid or flexible).
- Viral NA is in a hollow cylindrical capsid with a helical structure.
- Most helical viruses have envelopes.
Icosahedral/Polyhedral Viruses
- Common shape for many animal, plant, and bacterial viruses.
- Capsid is an icosahedron with 20 triangular faces and 12 corners.
- Capsomers form equilateral triangles.
- Some may have an envelope.
Complex Viruses
- Have complicated structures, often including bacterial viruses (bacteriophages).
- Often have a polyhedral head and a helical tail sheath.
- Examples include bacteriophages and poxviruses
Viral Proteins
- Capsid proteins protect viral genome/mediate attachment of virus to host cell receptors. Species and organ specificity are determined here.
- Outer viral proteins stimulate Ab production by the host and activate cytotoxic T-cells.
- Internal viral proteins may be structural or enzymes (RNA polymerase, DNA polymerase etc).
- Some viruses produce proteins that act as superantigens
- Human cells do not have these enzymes in their core mechanisms, so the virus often has to provide them itself inside a capsid
Atypical Virus-Like Agents
- Defective viruses
- Pseudovirions
- Viroids
- Prions
- Misfolded prion proteins can induce other proteins to misfold into prion form
Viral Replication/Multiplication
- For a virus to replicate, it has to invade a host cell and take over its metabolic machinery.
- Bacteriophages have two main replication cycles: lytic and lysogenic.
- Animal viruses also undergo replication steps, varying from host species and virus to virus, but they always require host cells to replicate
Lytic Cycle
- Attachment (adsorption): virus attaches to host cell
- Penetration: virus injects its DNA, often through a phage lysozyme
- Biosynthesis: viral genes are expressed
- Maturation (assembly): viral pieces are assembled into complete virions
- Release (lysis): host cell is broken open, releasing viral progeny
Lysogenic Cycle
- Phage DNA integrates into the host cell's DNA (now called a prophage).
- Host cell replicates normally, with the prophage DNA replicated as well, with no virus replication in this phase/cycle.
- The prophage can excise from the host's DNA, initiating the lytic cycle under certain conditions.
Replication of Animal Viruses
- Attachment
- Entry (often by endocytosis or fusion with the host cell membrane)
- Uncoating (releasing viral nucleic acid from the capsid)
- Biosynthesis (protein and nucleic acid synthesis)
- Maturation (assembly)
- Release (often by budding or lysis)
Viral Pathogenesis
- Viral infection can lead to several outcomes, such as:
- Viremia (virus in the blood)
- Over (infection is halted-immune responses)
- Tissue damage
- Latent viral infections (with periods of the virus being inactive and reactivation occurring)
- Autoimmune pathogenesis (immune reaction against the body's own tissues due to viral infection) - Example: measles causing encephalitis
- Oncogenic viruses that promote uncontrolled cell growth (e.g., Papillomavirus and others)
Host Defenses
- Nonspecific (innate) defenses:
- Interferons
- Natural killer (NK) cells
- Phagocytosis (macrophages, etc.)
- a-defensins, CXR4
- APOBEC3G
- Fever
- Mucociliary clearance
- Specific (adaptive) defenses:
- Active immunity
- Passive immunity
- Herd immunity
Antiviral Agents
- Drugs targeting the viral replication cycle
- Examples like Ganciclovir, Efavirenz, etc.
Specimen Selection and Collection
- Specimen collection depends on the virus and disease
- Collection is ideally done early in viral infection when viral titer is highest (typically first 4 days)
- Samples should be collected, ideally, at the infected site directly. An exception is certain viral infections of the CNS. In such cases, stool or throat samples are preferred for culture over CSF.
- Samples should be stored using viral transport media.
Laboratory Diagnosis
- Methods for detecting, culturing, and identifying viruses Include:
- Cytological or histological examination
- Electron microscopy
- Virus isolation in cell or tissue culture (SVCE)
- Direct antigen/gene detection (DFA, ELISA, PCR)
- Serological detection of viral antibodies
Viral Vaccines
- Active immunity can be elicited through vaccines containing a live, attenuated (weakened) virus, inactivated (killed) virus, or purified viral proteins.
- Examples include vaccines for measles, mumps, rubella (MMR), polio (live and inactivated), Hepatitis A, B, varicella, influenza, rabies.
- Passive immunity is provided by preformed antibodies from immune globulins (either human or animal origin).
- Passive-active immunity combines passive (immediate) and active (sustained long term protection) approaches.
- Rabies and Hepatitis B are examples of viruses using this two pronged approach.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Related Documents
Description
Test your knowledge of the lytic and lysogenic cycles in viral genetics. Answer questions about phage injection, prophages, and vaccine-related risks. This quiz covers key concepts essential for understanding bacteriophages and their interaction with bacterial cells.
