viruses (exam 3) Flashcards
. What are the unique characteristics of viruses?
Minuscule, acellular, infectious agents with DNA or RNA; obligate intracellular parasites; lack metabolic pathways, membranes, and organelles.
What are the two main components of a virus?
Protein (capsid) and nucleic acid (DNA or RNA).
What are the three main shapes of viruses?
Helical, polyhedral (icosahedral), and complex.
What is the difference between naked and enveloped viruses?
Enveloped viruses have a phospholipid membrane around the capsid, while naked viruses lack this membrane.
What is a virion?
The extracellular state of a virus, consisting of a capsid surrounding nucleic acid, sometimes with an envelope.
What is the host range of a virus?
The spectrum of host cells a virus can infect, determined by receptor compatibility.
What are the five stages of lytic replication in bacteriophages?
Attachment, entry, synthesis, assembly, and release.
- How does lysogenic replication differ from lytic replication?
Lysogenic replication integrates viral DNA into the host genome (prophage), delaying lysis; lytic replication immediately kills the host.
What is a prophage?
Inactive bacteriophage DNA integrated into a bacterial host’s genome during lysogeny.
What is lysogenic conversion?
When a prophage introduces new genes (e.g., toxins) that alter the host bacterium’s phenotype.
Where does DNA virus replication occur in animal cells?
Typically in the nucleus (e.g., herpesvirus).
Where does RNA virus replication occur in animal cells?
Typically in the cytoplasm (e.g., poliovirus).
What is a retrovirus?
An RNA virus that uses reverse transcriptase to convert its RNA genome into DNA (e.g., HIV).
What is a provirus?
Viral DNA integrated into a host cell’s genome (e.g., HIV provirus).
What enzyme do retroviruses carry?
Reverse transcriptase.
How do enveloped viruses acquire their envelope?
By budding from the host cell membrane, taking a portion of the membrane with them.
What are spikes on animal viruses?
Glycoproteins that mediate attachment to host cells.
- What is a latent viral infection?
A dormant state where the virus remains in the host without producing virions (e.g., HSV-1).
What is a persistent viral infection?
Slow release of virions over time without immediately killing the host (e.g., HIV).
How do viruses cause cancer?
By inserting oncogenes, disrupting tumor suppressor genes, or promoting uncontrolled cell division (e.g., HPV, EBV).
What is antigenic drift?
Minor mutations in viral genes (e.g., influenza H/N spikes) leading to small changes in antigens.
What is antigenic shift?
Major changes in viral antigens due to reassortment of genome segments (e.g., influenza A).
Why is influenza A prone to antigenic shift?
It infects multiple species (e.g., birds, pigs), allowing genome segment mixing.
What is the difference between communicable and noncommunicable diseases?
Communicable diseases spread between hosts; noncommunicable diseases do not (e.g., tetanus).
What is a contagious disease?
A communicable disease that spreads easily (e.g., measles).
- What is the difference between a portal of entry and exit?
Entry: How pathogens enter the host (e.g., respiratory tract). Exit: How they leave (e.g., feces).
What is the parenteral route?
Pathogen entry through breaks in the skin (e.g., needles, bites).
What is the difference between infection and disease?
Infection: Pathogen colonization; Disease: Symptoms/damage from infection.
- What is the difference between a symptom and a sign?
Symptom: Subjective (e.g., pain); Sign: Objective (e.g., fever).
What are resident microbiota?
Microbes that permanently colonize the host.
What are transient microbiota?
Microbes temporarily present in/on the host.
List Koch’s postulates.
1) Pathogen present in diseased hosts; 2) Isolated and grown in culture; 3) Causes disease when introduced to healthy host; 4) Re-isolated from new host.
What is the purpose of Koch’s postulates?
To establish a causal link between a microbe and a disease.
What are limitations of Koch’s postulates?
Fails for unculturable microbes, asymptomatic carriers, and polymicrobial diseases.
What is ID50?
Infectious dose for 50% of a population; measures virulence.
What is LD50?
Lethal dose for 50% of a population; measures toxicity.
What is the function of hyaluronidase?
Breaks down hyaluronic acid in connective tissue to promote pathogen spread.
What is the function of collagenase?
Degrades collagen in tissues to facilitate invasion.
What are the three types of exotoxins?
Cytotoxin, enterotoxin, neurotoxin.
What is an endotoxin?
Lipopolysaccharide (LPS) in Gram-negative bacterial cell walls; causes fever/shock.
How do AB toxins work?
B subunit binds host cell; A subunit enters and disrupts cellular functions (e.g., botulinum toxin).
What does botulinum toxin do?
Blocks acetylcholine release, causing paralysis.
What are the five stages of infectious disease?
Incubation, prodromal, illness, decline, convalescence.
How do capsules act as virulence factors?
Resist phagocytosis and enhance adhesion.
What is antigenic variation?
Pathogens alter surface antigens to evade immunity (e.g., Neisseria gonorrhoeae).
How does Neisseria achieve antigenic variation?
Gene recombination changes pilin proteins.
What are four ways virulence factors promote infection?
Adhesion, immune evasion, toxin production, and tissue invasion.
Why are virulence factors advantageous to microbes?
Enhance survival, transmission, and host damage.
Why is adhesion critical for infection?
Ensures pathogens attach to host cells/tissues to colonize and invade.
