The first electron micrographs of the Tobacco Mosaic Virus were captured in 1939 by Kausche, Pfankuch, and Ruska. This milestone was significant in virology as it provided the first direct visual evidence of the virus's rod-shaped structure, confirming earlier biochemical findings about its size and morphology.
602
What is the primary mechanism by which viruses propagate?
Viruses are obligate intracellular parasites that lack the machinery for independent reproduction. They propagate by hijacking the host cell's metabolic processes to synthesize viral components, a process known as viral replication. This involves the assembly of new virions within the host cell, which are subsequently released to infect other cells.
603
Which of the following structures is described as a fine protein filament extending from the bacterial surface?
Fimbriae are short, hair-like appendages composed of protein subunits called pilins. They are primarily involved in the attachment of bacteria to surfaces or host cells, playing a critical role in colonization and biofilm formation. Unlike flagella, they are not typically involved in motility.
604
During which century did smallpox outbreaks significantly impact populations?
Smallpox has a long history, with evidence of the disease appearing in various centuries. The 12th century is often cited in historical records regarding the prevalence and spread of the disease in different regions, contributing to its status as a major historical pathogen.
605
Which viral replication cycle is characterized by the integration of the viral genome into the host chromosome without causing immediate cell lysis?
In the lysogenic cycle, the viral DNA integrates into the host bacterial genome, becoming a prophage. The host cell continues to replicate and divide normally without bursting. The virus remains dormant until environmental triggers induce it to enter the lytic cycle, which eventually leads to cell destruction.
606
Which organism is commonly found as part of the human microbiome on the skin or in the nasal passages without typically causing disease?
Staphylococcus species, particularly Staphylococcus epidermidis, are common commensal bacteria that colonize human skin and mucous membranes. While they are generally harmless, they can act as opportunistic pathogens if they breach the skin barrier or enter the bloodstream, especially in immunocompromised individuals.
607
Which taxonomic class includes the Tobacco Mosaic Virus (TMV)?
Tobacco Mosaic Virus (TMV) is a well-studied plant virus belonging to the genus Tobamovirus. In modern viral taxonomy, it is classified within the class Virgaviricetes. This class encompasses various rod-shaped, positive-sense single-stranded RNA viruses that infect a wide range of plant hosts, causing significant agricultural damage.
AIDS (Acquired Immunodeficiency Syndrome) is caused by the Human Immunodeficiency Virus (HIV). The virus attacks the immune system, specifically targeting CD4 cells, which leads to a weakened immune response and makes the body susceptible to opportunistic infections and cancers.
609
What enzyme is encoded by the Tobacco Mosaic Virus (TMV) genome?
TMV is a positive-sense single-stranded RNA virus that encodes an RNA-dependent RNA polymerase (RdRp). This enzyme is essential for the replication of the viral genome within the host plant cell.
610
Which cellular system do viruses utilize to synthesize their components?
Viruses lack ribosomes, enzymes, and the energy-producing machinery required for protein synthesis and genome replication. Consequently, they must enter a host cell and commandeer its biosynthetic machinery, including ribosomes, tRNAs, and ATP, to produce viral proteins and replicate their genetic material.
