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).
