BIO by M Tahir ( Lecturer Al Azhar )

Icosahedral viruses have a highly symmetrical capsid composed of 20 triangular faces, providing maximum stability.

Helical viruses have capsomeres arranged helically around the viral nucleic acid, producing a rod-like appearance.

Tobacco Mosaic Virus (TMV) is a classic example of a helical, positive-sense single-stranded RNA virus infecting plants.

Viral envelopes originate from host cell membranes and contain viral glycoproteins essential for attachment and entry.

Naked viruses possess only a nucleic acid core surrounded by a protein capsid and are generally more resistant to environmental conditions.

TMV infects tobacco and many related plants but cannot infect animal cells because of host specificity.

T4 bacteriophage possesses an icosahedral head, helical tail, and tail fibers, making it the classic example of a complex virus.

Hepatitis B virus is a partially double-stranded DNA virus belonging to the Hepadnaviridae family. It replicates through reverse transcription but is classified as a DNA virus.

Positive-sense ssRNA viruses can be translated immediately by host ribosomes upon entering the host cell.

Human Immunodeficiency Virus (HIV) is a retrovirus containing single-stranded RNA and the enzyme reverse transcriptase.

Lipid envelopes are easily disrupted by heat, drying, soaps, and detergents, making enveloped viruses less stable outside the host.

Influenza virus infects humans, birds, and several mammals, therefore it belongs to the animal viruses.