GE 21 Virus Deck 2 Flashcards
What is the significance of tobacco mosaic disease?
First virus discovered, infects tobacco plants, led to understanding viruses are non-cellular, smaller than bacteria, and can crystallize.
Pioneered virology research and showed viruses could function outside host cells.
What is a virion?
Complete virus particle outside a host, contains genome (DNA or RNA), capsid (protein coat), some have lipid envelopes.
Inert outside cells but hijack host machinery for replication.
What are the three evolutionary scenarios for virus origins?
- Regressive hypothesis: evolved from complex ancestors
- Progressive hypothesis: mobile genetic elements gained ability to move between cells
- Virus-first hypothesis: viruses predate cellular life
Each hypothesis presents a different perspective on the origins of viruses.
Define acellular.
Not made of cells, no metabolism, growth, homeostasis, cannot reproduce independently, rely on host cell machinery.
Composed of genetic material (RNA/DNA), capsid, sometimes envelope.
What are the two components all viruses have?
- Genome (DNA or RNA, single or double-stranded)
- Capsid (protein shell) protects genome and helps attach to host cells
Some viruses also have lipid envelope and glycoproteins for host recognition.
What are capsids composed of?
Repeating subunits called capsomeres, protects nucleic acid, aids host attachment, and entry.
Key shapes include helical, icosahedral, and complex.
What is the function of viral envelopes?
Lipid bilayer derived from host cell membrane, aids in host attachment, immune evasion, and fusion with host membrane.
More sensitive to disinfectants than non-enveloped viruses.
What are bacteriophages?
Viruses that infect bacteria, have complex structures, inject DNA into bacteria, can follow lytic or lysogenic cycles.
Used in phage therapy as an antibiotic alternative.
What are capsomeres?
Protein subunits forming capsid, self-assemble into various shapes, influence viral stability and immune system recognition.
Structural proteins encoded by viral genes.
List the four groups of viral classification based on capsids.
- Helical
- Icosahedral
- Complex
- Enveloped
Capsid structure affects host interaction, stability, and immune evasion.
What are viral receptors and their importance?
Host cell surface molecules viruses bind to for entry, determine host range and tissue tropism.
Blocked by antibodies and antiviral drugs.
How are viruses classified by genome structure?
- DNA vs. RNA
- Single-stranded (ss) vs. Double-stranded (ds)
- Positive-sense vs. Negative-sense RNA
Determines replication strategy, enzyme needs, and mutation rate.
What is the Baltimore Classification?
Groups viruses based on mRNA synthesis, includes 7 groups: dsDNA, ssDNA, dsRNA, +ssRNA, -ssRNA, retroviruses, DNA RT viruses.
Key for understanding replication strategies.
What are obligate intracellular parasites?
Viruses that cannot reproduce outside host, rely on host enzymes and ribosomes.
Infect all life forms.
Define cytopathic effects.
Virus-induced cellular changes including cell lysis, apoptosis, syncytia formation, and inclusion bodies.
Causes tissue damage and inflammation.
What is the difference between lysis and apoptosis?
- Lysis: virus bursts host cell, releases virions
- Apoptosis: programmed cell death, limits viral spread
Some viruses delay apoptosis to increase replication.
List the six basic steps in viral infection.
- Attachment
- Entry
- Uncoating
- Replication
- Assembly
- Release
Release can occur via lysis or budding.
What occurs during the lytic cycle?
Virus rapidly replicates inside the host cell, leading to host cell destruction and release of new viruses.
Example: T4 bacteriophage.
What happens during the lysogenic cycle?
Viral genome integrates into host genome, remains dormant, can reactivate into lytic cycle.
Example: Lambda phage, HIV latency.
Define a prophage.
Integrated viral genome in bacterial DNA, passed to daughter cells during division.
Can later activate into the lytic cycle.
What is latency in viruses?
Virus remains dormant in host with no active replication, can reactivate under stress.
Examples: Herpes, HIV.
Differentiate between horizontal and vertical transmission.
- Horizontal: person-to-person, vectors, surfaces
- Vertical: mother-to-child (placenta, birth, milk)
Key for understanding transmission routes.
What is the difference between hyperplasia and hypoplasia?
- Hyperplasia: excessive cell growth
- Hypoplasia: underdevelopment
Relevant in the context of viral infections and their effects.
What is cell necrosis?
Uncontrolled cell death due to infection, triggers inflammation.
Important in understanding tissue damage.
