Characteristics of Viruses
📌 Viruses possess dual characteristics, acting as both living and non-living entities; they are considered living because they can replicate within a host cell using nucleic acids (DNA or RNA).
🔬 Viruses are classified as non-living because they can be crystallized and are acellular, lacking cytoplasm, nucleus, and organelles.
📏 Viral body sizes are extremely small, ranging from 20 nm to 400 nm in diameter, requiring an electron microscope for visualization.
🦠 Structurally, viruses like bacteriophages consist of a head (containing nucleic acid), a neck, and a tail, while influenza viruses have components like membranous proteins and the nucleocapsid.

Virus Classification and Structure
🧬 Based on nucleic acid content, viruses are classified as riboviruses (RNA, e.g., Coronavirus, Orthomyxovirus) or deoxyriboviruses (DNA, e.g., Bacteriophage, Herpesvirus).
⏹️ Basic viral shapes include polyhedral (like Adenovirus), helical (like Tobacco Mosaic Virus - TMV), spherical/enveloped (like Influenza), and complex (like Bacteriophage).
🏘️ Viruses are also grouped by their host cell, infecting humans (e.g., Hepatitis virus), animals (e.g., Paramyxovirus), plants (e.g., TMV), or bacteria (Bacteriophage).

Viral Replication Mechanisms
🌀 Viral reproduction occurs via replication inside a suitable host cell, observable clearly in bacteriophages infecting *Escherichia coli*.
💥 The lytic cycle results in the destruction of the host cell and the formation of new viral particles, involving stages: adsorption, penetration, e-clipse, formation, assembly, and lysis.
🔁 The lysogenic cycle involves the host cell integrating viral nucleic acid (becoming a prophage) without immediate destruction, allowing the cell to divide and pass on the viral genome before potential later synthesis and lysis.

Beneficial and Harmful Roles of Viruses
🌟 Beneficial viruses include interferon, which prevents viral replication; prophages, which can alter bacterial phenotypes useful in medicine; and vaccines, which stimulate antibody production.
☣️ Harmful viruses mentioned include Rice Tungro Bacilliform Virus (RTBV) attacking rice, TMV causing yellow spots on tobacco leaves, and Orthomyxovirus causing human respiratory infections.
🛡️ Prevention against viral diseases involves vaccination, adopting a healthy lifestyle, and avoiding fluid contact with infected individuals or animals.

Key Points & Insights
➡️ Viruses exhibit characteristics of both living (replication) and non-living (crystallization) matter.
➡️ Key structural components like the nucleic acid (DNA or RNA) are responsible for controlling replication activities within the host.
➡️ The two primary reproductive cycles are the lytic cycle (cell destruction) and the lysogenic cycle (integration as a prophage).
➡️ Proactive steps for protection include vaccination and maintaining a healthy lifestyle.

📸 Video summarized with SummaryTube.com on Nov 27, 2025, 05:55 UTC