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A comprehensive set of flashcards covering viruses, viroids, prions, emerging diseases, and prokaryotic biology (bacteria and archaea).
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What genetic material do viruses possess?
Either DNA or RNA, never both.
Can viruses evolve?
Yes, viruses can evolve over time.
Why are viruses called obligate intracellular parasites?
Because they can replicate only inside a host cell.
Who coined the term “virus” and in what year?
Louis Pasteur in 1884.
What does the Latin word ‘virus’ mean?
Poison.
What key finding did Ivanowsky make in 1892 about tobacco mosaic disease?
Filtered sap free of bacteria could still cause the disease, implying an agent smaller than bacteria.
Why is viral classification difficult?
Viruses mutate rapidly and are not considered living organisms.
List the taxonomic levels used for viruses.
Order, family, genus, species.
Roughly how many viral species are known today?
More than 2,500.
What system is used to classify new variants within the same viral species?
Subtypes (e.g., H and N types in influenza).
Name the two main structural parts of a virus particle.
Covering and inner core.
What does a viral covering include?
Protein capsid and, in some viruses, a lipid envelope.
What is found in the inner core of a virus?
Nucleic acid (DNA or RNA) and viral proteins/enzymes.
Define viral capsid.
The protein coat made of repeating protein subunits.
What is a viral envelope and its origin?
A lipid membrane surrounding some viruses; it is derived from the host cell membrane.
What are viral glycoproteins?
Proteins encoded by the viral genome that protrude from the envelope and aid in attachment.
What is a naked virus?
A virus lacking an envelope.
Describe the structure of Tobacco Mosaic Virus.
RNA virus with a helical capsid.
Describe the structure of a T-even bacteriophage.
DNA virus with a polyhedral head and helical tail with fibers and base plate.
Describe the structure of the influenza virus.
RNA virus with spherical capsid, envelope, and surface spikes.
What is host specificity?
A virus can infect only particular species or cell types.
Define tissue tropism.
Restriction of a virus to specific tissues that bear the right receptors.
List the five general steps of viral reproduction.
Attachment, penetration, biosynthesis, maturation, release.
What happens in the lytic cycle?
The host cell is lysed, releasing new viruses and causing cell death.
What is a prophage?
Latent viral DNA integrated into a host’s chromosome during the lysogenic cycle.
How can a lysogenic virus become lytic?
Environmental stressors can trigger activation to the lytic cycle.
During viral latency, what is occurring?
Viral DNA replicates with host DNA, but virions are not produced.
Give an example of toxins produced due to lysogenic conversion.
Toxins produced in scarlet fever.
How do many enveloped animal viruses enter host cells?
Fusion of their envelope with the host membrane.
How do many naked animal viruses enter host cells?
Endocytosis by the host cell.
What is uncoating in animal viruses?
Removal of capsid (and envelope) to release genetic material.
Name a highly virulent virus that rapidly destroys host cells.
Ebola virus.
How are enveloped animal viruses often released?
Budding, acquiring a host-derived envelope.
How do naked animal viruses typically exit the host cell?
By causing lysis of the host cell.
What are bacteriophages?
Viruses that infect bacteria.
What is phage therapy?
Using bacteriophages to treat bacterial infections.
What is a retrovirus?
An RNA animal virus that converts its RNA into DNA via reverse transcriptase.
Give an example of a retrovirus.
HIV.
Define viroids.
Naked strands of RNA with no capsid that infect plants.
Define prions.
Infectious proteins with abnormal conformation causing neurodegenerative diseases.
Name diseases caused by prions.
Transmissible spongiform encephalopathies (e.g., mad cow disease).
What is an emerging infectious disease?
A disease appearing for the first time in humans or increasing rapidly in incidence or geographic range.
List factors that drive emerging viral outbreaks.
Changes in transmission, lack of immunity, and viral mutation.
Which two domains make up the prokaryotes?
Bacteria and Archaea.
Who first described prokaryotes as “animalcules”?
Antonie van Leeuwenhoek.
What concept did Louis Pasteur disprove?
Spontaneous generation.
What did Pasteur’s swan-neck flask experiment demonstrate?
Airborne microbes contaminate broth; without contaminants, no growth occurs.
Name the three main structural regions of a prokaryotic cell.
Cell envelope, cytoplasm, appendages.
Components of a prokaryotic cell envelope include…
Plasma membrane, cell wall, glycocalyx.
What is the bacterial cell wall made of?
Peptidoglycan.
Function of the glycocalyx?
Attachment and protection from host immune response.
Where is the bacterial chromosome located?
In the nucleoid region of the cytoplasm.
Role of prokaryotic ribosomes?
Protein synthesis.
Define fimbriae.
Short bristle-like structures for attachment to surfaces.
What is a conjugation pilus?
Hollow appendage for DNA transfer between bacteria.
What is the primary means of reproduction in bacteria?
Binary fission (asexual).
What is horizontal gene transfer?
Transfer of genes between bacteria by non-reproductive means.
Differentiate conjugation, transformation, and transduction.
Conjugation: plasmid transfer via pilus; Transformation: uptake of free DNA; Transduction: DNA transfer by bacteriophage.
Purpose of the Gram stain?
To distinguish Gram-positive from Gram-negative bacteria based on cell wall structure.
Describe Gram-positive cell walls.
Thick peptidoglycan layer outside the plasma membrane; stain purple.
Describe Gram-negative cell walls.
Thin peptidoglycan sandwiched between inner & outer membranes; stain pink/red.
Why are Gram-negative bacteria more antibiotic-resistant?
Their outer membrane blocks many antibiotics.
Name the three common bacterial shapes.
Cocci (spherical), bacilli (rod), spirilli (spiral).
What does ‘staph-’ indicate in bacterial arrangement?
Clusters.
What does ‘strept-’ indicate?
Chains.
Define aerobic bacteria.
Bacteria that require oxygen for cellular respiration.
Define facultative anaerobe.
Can grow with or without oxygen.
Define obligate anaerobe.
Cannot grow in the presence of oxygen.
What are photoautotrophs?
Photosynthetic bacteria using light to reduce CO₂.
Differentiate oxygenic vs anoxygenic photosynthesis.
Oxygenic (produces O₂, uses PSI & PSII); Anoxygenic (no O₂, uses PSI only).
What are chemoautotrophs?
Bacteria that oxidize inorganic compounds and fix CO₂.
What are chemoheterotrophs?
Bacteria obtaining both carbon and energy from organic molecules.
Define saprotroph.
Organism that decomposes dead organic matter; many pathogenic bacteria are saprotrophs.
How do bacterial toxins cause disease?
They disrupt host processes, causing symptoms like food poisoning or shock.
What are LPS and why dangerous?
Lipopolysaccharides in Gram-negative walls; they overstimulate immune response, causing shock.
What are superantigens?
Proteins that hyper-activate immune cells, leading to shock.
Define endospore.
Highly resistant dormant structure formed inside some bacteria.
Name three genera that produce endospores.
Clostridium botulinum, Clostridium tetani, Bacillus anthracis.
When do endospores germinate?
When environmental conditions become favorable.
What is the action of penicillins & vancomycin?
Inhibit peptidoglycan synthesis, weakening cell walls.
How do tetracyclines & erythromycin act?
Bind bacterial ribosomes, blocking protein synthesis.
Mechanism of sulfonamides & quinolones?
Inhibit bacterial nucleic acid synthesis.
Do antibiotics harm human cells?
No; they selectively target bacterial structures/processes.
Key biochemical trait distinguishing Archaea from bacteria?
Unique membrane lipids (branched hydrocarbons linked to glycerol).
Do Archaea have peptidoglycan?
No.
Name three major groups of Archaea.
Methanogens, halophiles, thermoacidophiles.
Where are methanogens found and what do they produce?
Anaerobic habitats (swamps, intestines); produce methane from H₂ and CO₂.
What conditions do halophiles require?
High salt concentrations (12–15%).
Describe thermoacidophiles.
Archaea thriving in extremely hot, acidic environments such as hot springs.