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Viruses
| Question | Answer |
|---|---|
| Why Does The Central Dogma Have To Move From DNA → RNA → Proteins? | DNA serves as a stable, long-term store of genetic information, while RNA acts as a temporary, flexible messenger that protects DNA and regulates expression. Proteins are the final products. |
| Virus | a genetic element that can multiply only in a living (host) cell. Not living, not found on the tree of life. |
| Obligate intracellular parasite (virus): | needs host cell for energy, metabolic intermediates, protein synthesis. Has its nucleic acid genome. |
| Virus Particle (Virion): | extracellular form of virus. Exists outside the host and facilitates transmission from one host cell to another. Replication/reproduction occurs only upon infection (entry into the host cell). |
| Baltimore Classification: | a system that categorizes viruses into seven classes based on their type of nucleic acid (DNA or RNA), strandedness (single or double), and how they replicate to produce mRNA. |
| Viral Diversity and Hosts | Viruses can have either DNA or RNA genomes, unlike cells which always use DNA. Their genomes may be single-stranded (ss) or double-stranded (ds). |
| Naked Viruses | Structure: Protein capsid only, no lipid membrane Stability: More resistant to drying, heat, detergents, and stomach acid Transmission: Often via fecal–oral route Release from cell: Typically by lysis (bursting the host cell). |
| Enveloped Viruses | Structure: Capsid surrounded by a lipid bilayer envelope derived from the host cell membrane. Stability: Less resistant, envelope is sensitive to drying, heat. Transmission: Usually via direct fluid exchange Release from cell: Often by budding |
| Lysozyme (Viral Enzymes): | creates openings in bacterial cell walls to allow the viral nucleic acid to enter the host cell, and later helps break down the cell wall to release newly assembled viral particles. |
| Neuraminidases (Viral Enzymes): | important in influenza viruses. Break down glycoproteins and glycolipids on the host cell surface, which facilitates the release of new viral particles from infected cells. |
| RNA-dependent RNA polymerases (Viral Enzymes): | essential for RNA viruses because host cells typically don't have the machinery to replicate RNA from an RNA template. These viral enzymes allow RNA viruses to replicate their genetic material inside the host cell. |
| Reverse transcriptase (Viral Enzymes): | found in retroviruses (like HIV) and allows these RNA viruses to create DNA copies of their RNA genome. This DNA can then integrate into the host cell's chromosome, which is how retroviruses establish persistent infections. |
| Bacterial Viruses Laboratory Growth: | Where viruses are present, they infect and kill bacteria, creating clear zones called “plaques.” They're clear plaques against the cloudy bacterial lawn. Each plaque is the area where a virus replicated and spread, killing the bacteria in that zone. |
| Animal and Plant Viruses Laboratory Growth: | require much more complex cultivation methods because they can only replicate inside living eukaryotic cells. Researchers must grow cells from organs in specialized culture medium, using plant tissue cultures (like hairy root systems) in liquid medium. |
| CFU | colony forming unit, fancy term for that one cell that formed a colony. |
| PFU | plaque forming unit, term used for plaque assay |
| Five steps of viral replication in a permissive (supportive) host: | attachment, penetration, synthesis, assembly, and release. |
| Most important step of viral replication: | attachment. |
| Steps of the lytic cycle of bacteriophages (viruses that infect bacteria): | Attachment - virion attaches to cell Penetration - DNA is injected, protein coat remains outside Synthesis - host cell machinery hijacked Assembly - New virus particles are assembled Lysis - host cell bursts, releasing virions to infect other cells |
| Lytic pathway | Proceeds directly to viral replication and host cell destruction, as shown in the first image. |
| Lysogenic pathway | viral DNA integrates into the host chromosome, creating a “prophage” that remains dormant. The lysogenized cell can reproduce normally, passing the viral DNA to its offspring. Under certain conditions, the prophage can revert to the lytic cycle. |
| Animal Virus Infection Outcomes: | Transformation: virus causes normal cells to become tumor cells Lysis: Cell death with virus release Persistent infection: Continuous virus release without killing the host cell Latent infection: Virus remains dormant but can reactivate |
| Archaeal Viruses Key Characteristics: | All known archaeal viruses have DNA genomes and most have double-stranded circular DNA |
| Archaeal Viruses Morphological Diversity: | comes in various shapes including icosahedral (geometric), filamentous (thread-like), pleomorphic (variable shape), and bottle-shaped forms. |
| Fifth Disease (Parvo-Virus): | A mild childhood viral infection caused by parvovirus B19 that produces a distinctive bright red "slapped cheek" facial rash followed by a lacy body rash. |
| Lymes Disease: | A bacterial infection transmitted by infected deer ticks that causes a characteristic bull's-eye rash, flu-like symptoms, and can lead to serious joint, heart, and neurological problems if untreated. |
| Chicken Pox Parties: | Deliberate gatherings where parents intentionally expose their healthy children to someone with chickenpox so they'll contract the disease and develop natural immunity before adulthood. |
| Shingles: | A painful viral infection caused by the reactivation of the dormant chickenpox virus (varicella-zoster) in adults, typically appearing as a painful, blistering rash along one side of the body following a nerve pathway. |
| Attachment (Bacteriophage vs. Animal Cell) | Attaches to the cell wall, Attaches to the cell membrane |
| Entry (Bacteriophage vs. Animal Cell) | Inject genetic material, penetrates viral nucleic acid vs. Endocytosis fusion, the virus is engulfed by a vesicle |
| Synthesis/Assembly (Bacteriophage vs. Animal Cell) | Occurs inside the host cell cytoplasm vs. Cytoplasm nucleus, Golgi, ER |
| Release (Bacteriophage vs. Animal Cell) | Lysis or Lysogeny Vs. Budding, exocytosis, lysis |
Created by:
smurtab