Martinus W. Beijerinck coined the term ‘virus’ in 1898 to describe the infectious agent of tobacco mosaic disease.

The electron microscope, invented in the 1930s, provided the resolution needed to visualize viral structures.

Viruses have either DNA or RNA as their genetic material, never both simultaneously, and rely on host cells for replication.

Influenza is caused by orthomyxoviruses (myxoviruses), which are single-stranded RNA viruses.

The envelope is a lipid bilayer surrounding some viruses, derived from the host cell membrane.

Bacteriophages are viruses that infect bacteria, typically containing double-stranded DNA.

Most plant viruses have single-stranded RNA as their genetic material, enabling replication in plant cells.

Many animal viruses, like adenoviruses, have polyhedral (icosahedral) capsids, though some are helical.

Bacteriophages have a complex capsid with an icosahedral head and helical tail, unique to their function.

Viruses are obligate parasites, requiring a host cell to replicate and perform metabolic activities.

Many animal viruses, like influenza, exhibit helical symmetry in their capsid structure.

AIDS is caused by HIV, a retrovirus that integrates its RNA-derived DNA into the host genome.

The Baltimore Classification groups viruses into seven classes based on genome type and replication strategy.

Potato spindle tuber disease is caused by viroids, small RNA molecules without a protein coat.

Most plant viruses are transmitted by insect vectors, like aphids, during feeding.

Polio is caused by poliovirus, while tetanus and diphtheria are caused by bacteria.

Plant viral infections cause necrosis (cell death), mosaic formation (patchy discoloration), and chlorosis (yellowing).

Theodor Diener discovered and named viroids in 1971 while studying potato spindle tuber disease.

Viroids are small, single-stranded RNA molecules without a protein coat, unlike viruses.

Viruses consist of a protein capsid and nucleotide-based genetic material (DNA or RNA).

Viroids interfere with host plant RNA processing, causing abnormal gene expression and disease symptoms.

Tobacco mosaic virus has a rod-shaped, helical capsid structure.

Viruses require a host cell’s machinery to replicate, a defining feature of their parasitic nature.

RNA viruses use RNA as their genetic material, demonstrating RNA’s hereditary role.

Viruses require living host cells for culture, not artificial nutrient media.

PSTV (Potato Spindle Tuber Viroid) has less genetic material (359 nucleotides) than even the smallest viruses.