Chapter 6 Flashcards
(27 cards)
What is the size of a virus relative to a bacterium?
Viruses are much smaller than bacteria.
Viruses generally range from about 20–300 nanometers in diameter, while most bacteria are around 1–2 micrometers in size, making viruses roughly 10–100 times smaller than typical bacteria.
How is a virus able to maintain so many fewer genes than a bacterium?
Viruses rely on their host cells for many functions.
They encode only the essential proteins required for entry, replication, and assembly.
What is a virus?
Viruses are acellular infectious agents.
They consist of genetic material (either DNA or RNA) and a protective protein coat (capsid). Some viruses also have an envelope derived from the host cell membrane.
What is the basic structure of a virus? What is the function of these pieces?
Key components include the genome, capsid, and envelope (if present).
The genome carries the viral genetic information, the capsid protects the genome and aids in attachment to host cells, and the envelope enhances attachment and fusion with host cell membranes.
What is the capsid? What is it made of?
The capsid is the protein shell of the virus.
It is composed of multiple copies of one or a few types of protein subunits called capsomeres.
What are viral plaques?
Viral plaques are areas of cell destruction.
They appear as clear zones on a lawn of cells, resulting from one virus infecting a cell, replicating, and spreading to neighboring cells, causing cell lysis.
What types of organisms are susceptible to viral infections?
Viruses infect every domain of life.
This includes bacteria (infected by bacteriophages), archaea, plants, animals, and fungi.
What is a bacteriophage?
A bacteriophage (or phage) is a virus that infects bacteria.
Bacteriophages play roles in regulating bacterial populations and can influence bacterial evolution through gene transfer.
How have viruses impacted human populations? How do they impact the agricultural industry?
Viruses are responsible for many diseases and can cause widespread illness.
In agriculture, plant viruses reduce crop yields and quality, while animal viruses can affect livestock health.
Why is it difficult to come up with anti-viral therapies?
Key challenges include host dependence, high mutation rates, and intracellular location.
Targeting viruses without harming host cells is challenging due to their reliance on host machinery.
How are viruses beneficial?
Viruses help control microbial populations and have biotechnological uses.
They are used in gene therapy, vaccine development, and facilitate horizontal gene transfer among organisms.
What is the host range? Do viruses all have the same host range?
The host range defines which organisms a virus can infect.
Some viruses have a narrow host range, while others have a broad host range, demonstrating variability in host specificity.
Are viruses all the same size?
There is considerable size variation among viruses.
While many viruses are small, some ‘giant viruses’ are much larger and more complex.
What types of genes are encoded for in a viral genome?
Viral genomes encode structural genes, replication enzymes, and accessory genes.
Structural genes encode proteins for the capsid and envelope, while replication enzymes are necessary for replicating the viral genome.
What are viroids? Prions?
Viroids are small, circular RNA molecules that lack a protein coat.
Prions are misfolded proteins that induce other proteins to adopt the same misfolded conformation, associated with neurodegenerative diseases.
What do prions do? From where do they originate?
Prions cause normal proteins to misfold and aggregate.
They originate from normal host proteins that have undergone a conformational change.
How can the cell membrane of the host become part of a virus?
Some viruses are enveloped.
Enveloped viruses acquire their lipid membrane by budding from the host cell.
How can genomic information become part of a virus? How is this information transformed to other hosts?
Genomic information can integrate into a host’s DNA or be packaged during viral replication.
Lysogeny involves a bacteriophage integrating its genome, while transduction can transfer bacterial DNA to another cell.
What are spike proteins? Tegument?
Spike proteins are glycoproteins that facilitate virus binding to host cells.
Tegument is a layer found in some viruses that contains proteins aiding in infection initiation.
What must occur for a virus to infect a host? What happens once it has infected the host?
Infection involves attachment, entry, uncoating, replication, assembly, and release.
New viruses exit the cell by lysis or budding.
What happens in host recognition and attachment?
Viruses attach to specific receptors on the host cell surface.
Bacteria do not have specialized ‘virus transporters’; viruses exploit existing bacterial surface proteins.
Understand the difference between and what happens in the lytic vs. lysogenic cycle.
In the lytic cycle, the virus rapidly replicates and causes cell lysis.
In the lysogenic cycle, the viral genome integrates into the host’s DNA and replicates with it.
What is a prophage?
A prophage is the viral genome integrated into a bacterial host’s chromosome.
It remains dormant until triggered to become active.
What is the signal for a prophage to become lytic?
Environmental stress triggers prophage activation.
Factors like UV radiation or chemical agents can cause the prophage to excise and initiate the lytic cycle.
