Intro to viruses

• Enveloped viruses have an additional lipid bilayer surrounding the capsid, derived from host cell membranes during assembly or budding.
• The nucleocapsid is composed of protein subunits that surround the genome, providing protection and stability.
• Non-enveloped viruses lack this outer layer and are more stable outside the body but less able to infect cells.
• Genetic Material


  Viruses can contain either DNA or RNA as their genetic material, but not both. This genetic material can be single-stranded or double-stranded, linear or circular.
• Capsid


  The protein coat that surrounds and protects the viral genetic material. It is made up of protein subunits called capsomeres, which can be arranged in various symmetrical patterns, such as helical, icosahedral, or complex.
• Envelope


  Some viruses have an additional lipid bilayer membrane surrounding the capsid, known as the envelope. This envelope is acquired from the host cell membrane during the process of viral budding. Enveloped viruses often have glycoprotein spikes embedded in the envelope.
• Shape and Size


  Viruses exhibit diverse shapes and sizes. Common shapes include spherical (icosahedral), rod-shaped (helical), and complex structures. Sizes can range from about 20 nanometers (nm) to several hundred nanometers.
• Attachment Structures


  Viruses may possess specific attachment structures such as spikes or fibers protruding from their capsid or envelope. These structures facilitate attachment to host cell receptors during the infection process.
• Classification


  Viruses are classified based on various factors including their morphology, genetic material, mode of replication, and host range. The Baltimore classification system categorizes viruses into seven groups based on their genome type and replication strategy.
• Viral Lifecycle


  1. Attachment and entry into host cells

  2. Replication of viral genetic material

  3. Assembly of new virions

  4. Release from the host cell
• Host Specificity


  Viruses exhibit specificity for particular host organisms or cell types due to interactions between viral attachment proteins and host cell receptors. This specificity influences viral tropism and pathogenesis.
• Viral Diversity


  • Viruses display immense diversity in their morphology and structure, reflecting their adaptation to various environments and host organisms. This diversity contributes to the wide array of diseases caused by viruses.
• Visualization


  Techniques such as electron microscopy, X-ray crystallography, and cryo-electron microscopy are used to visualize and study the structure of viruses at high resolution, providing insights into their organization and function.