Viruses: Structure and Replication

Viruses: Basic Characteristics

• Viruses are smaller than bacteria and animal cells.
• Viruses are not considered living for two reasons:
  • They need a host cell to replicate.
  • They cannot metabolize food for energy.

Viral Structure

• Viruses are made up of nucleic acids (DNA or RNA).
• They have a protein coat, also known as a capsid.
• The protein coat helps the virus attach to a host cell.

Viral Attachment

• For a virus to attach to a cell, the cell's receptors and the virus's proteins must match.

Viral Replication Cycles

• Viruses have two main replication cycles: lytic and lysogenic.
• Lytic cycle:
  • Virus infects a living cell.
  • New viral parts assemble inside the cell.
  • The new viruses destroy the cell (lyse it).
• Lysogenic cycle:
  • Virus infects a living cell.
  • Virus's DNA combines with the host cell's DNA.
  • The virus's DNA is inactive and does not harm the cell.
  • Cell replicates normally.
  • The lysogenic cycle can become lytic if the viral DNA separates from the host DNA.

Antivirals vs. Vaccines

• Antibiotics cannot kill viruses; they only kill bacterial diseases.
• Vaccines can prevent some viruses.

HIV

• HIV causes AIDS.
• HIV attacks helper T-cells, which are part of the immune system.
• HIV changes (mutates) very rapidly, making it difficult to develop a vaccine.
• The virus kills T-cells until the body loses its ability to fight off infections.

Explore the basic characteristics of viruses, including their structure and replication cycles. This quiz covers the differences between lytic and lysogenic cycles, as well as the components that make up a virus. Test your understanding of how viruses interact with host cells.