Study "Cell Biology", a flashcard deck on FORKSAI.
How did early scientists describe invisible infectious agents before the term 'virus' was widely adopted?
Prior to being able to see them, invisible infectious agents were described as 'contagium vivum fluidum,' meaning contagious living fluid. This term reflected the understanding that these agents were infectious and could spread disease, even though their nature was unknown.
What significant technological advancement in the 1930s allowed scientists to directly observe viruses for the first time?
The advent of the electron microscope in the 1930s allowed scientists to directly observe viruses for the first time. This breakthrough enabled the study of their structure and replication, moving beyond the previous understanding of them as merely filterable agents.
Define a 'virion' and explain its primary components.
A virion is a complete, fully developed, infectious viral particle that exists outside a host cell. It is composed of nucleic acid, which can be either DNA or RNA, and is surrounded by a protective protein coat called a capsid.
How do viruses differ from bacteria in terms of their cellular machinery and energy generation?
Viruses are obligatory intracellular parasites, meaning they lack ribosomes and ATP-generating mechanisms, relying entirely on the host cell's machinery for multiplication. In contrast, bacteria are typically free-living organisms that possess their own ribosomes and ATP-generating systems.
In what situation would the presence of spikes on a virus be particularly important for its infectivity?
Spikes are particularly important for viral infectivity during the attachment and entry phases into a host cell. For example, influenza viruses use hemagglutinin (H) spikes to attach to host cells and neuraminidase (N) spikes to detach from the cell surface during the release of new virions.
How did Dmitri Ivanovsky's experiment with tobacco mosaic disease contribute to the understanding of viruses?
Dmitri Ivanovsky passed infected sap through a bacteria-proof filter and found that the filtrate still caused disease in healthy plants. This led him to conclude that the infectious agent was either a toxin or something smaller than bacteria, providing early evidence for the existence of filterable, non-bacterial pathogens.
Distinguish between 'naked viruses' and 'enveloped viruses' based on their structural composition.
Naked viruses, also known as non-enveloped viruses, consist only of a nucleic acid genome surrounded by a protein capsid. Enveloped viruses, on the other hand, have their nucleic acid and capsid further surrounded by an outer lipid layer, which is a portion of the host cell's phospholipid membrane obtained during budding.
Why are viruses considered 'obligatory intracellular parasites'?
Viruses are considered obligatory intracellular parasites because they absolutely require living host cells to multiply. They lack their own ribosomes and ATP-generating mechanisms, meaning they must utilize the host cell's synthesizing machinery to replicate their genetic material and produce new viral particles.
What is the function of capsomeres in a virus?
Capsomeres are the individual protein subunits that make up the capsid, which is the protein coat surrounding the viral nucleic acid. These subunits assemble to form the protective structure that encloses the viral genome.
How does the variety of viral nucleic acid differ from the nucleic acid found in cellular organisms?
Viral nucleic acid can be either DNA or RNA, but never both, and can be single-stranded or double-stranded, linear, circular, or segmented. In contrast, cellular organisms typically have double-stranded DNA as their genetic material, with RNA primarily serving as an intermediary.