Lesson 3: Main components of viruses and their functions

Viruses consist of a few key components that enable them to infect host cells and replicate. The main components of viruses and their functions include:

1. Genetic Material (DNA or RNA):
   • Function: The genetic material of a virus carries the instructions needed for the virus to replicate and produce new viral particles. It contains the information necessary for the synthesis of viral proteins and the assembly of new virus particles. The genetic material can be either DNA or RNA, single-stranded or double-stranded, and linear or circular, depending on the type of virus.
2. Capsid:
   • Functions:
   • The capsid is the protein coat that surrounds and protects the viral genetic material
   • It plays a crucial role in the attachment of the virus to host cells.
   • The capsid is composed of protein subunits called capsomers, and its structure provides stability to the viral particle.
   • Interact specifically with the viral nucleic acid for packaging
   • Interact with vector for specific transmission
   • Interact with host receptors for entry to cell
   • Allow for release of nucleic acid upon entry into new cell
   • Assist in processes of viral and/or host gene regulation

1. Envelope (in Some Viruses):
   • Functions:
   • Some viruses have an outer envelope, which is a lipid membrane derived from the host cell membrane. The envelope contains viral glycoproteins that play a key role in the attachment of the virus to host cells. Enveloped viruses are often more sensitive to environmental conditions than non-enveloped viruses.
   • Viral envelope fuses with host’s membrane during internalization
   • Transports genome and capsid into cell
   • Protects nucleic acids
   • Stimulate the immune system to produce antibodies that can protect the host cells against future infections
2. Viral Envelope Proteins:
   • Function: Enveloped viruses have viral envelope proteins embedded in the lipid bilayer. These proteins are essential for the virus to interact with and enter host cells. They may be involved in binding to host cell receptors, membrane fusion, and other steps of the viral life cycle.
3. Spikes or Projections:
   • Function: Some viruses have spikes or projections on their surface, which are composed of viral proteins. These structures aid in the attachment of the virus to specific receptors on host cells.
4. Matrix Proteins (M proteins in Enveloped Viruses):
   • Function: Enveloped viruses often have matrix proteins located between the capsid and the envelope. These proteins help maintain the structural integrity of the virion and are important for the assembly and release of new virus particles.
5. Tail Fibers (in Some Bacteriophages):
   • Function: Bacteriophages, which infect bacteria, may have tail fibers or structures that assist in the attachment to and injection of the viral genetic material into bacterial cells.
6. Viral Enzymes (in Some Viruses):
   • Function: Some viruses carry specific enzymes within their structure. For example, retroviruses, like HIV, carry the enzyme reverse transcriptase, which is essential for converting viral RNA into DNA during the replication process.
     Other examples: RNA polymerase in viruses with (-) RNA genomes: Transcribe RNA to  mRNA or replicaation of RNA genome.

Understanding the functions of these viral components is crucial for studying the biology of viruses, developing antiviral drugs, and designing effective vaccines. The interaction between