Viruses are obligate intracellular parasites, meaning they can only replicate inside living cells. They lack the machinery to make their own proteins or replicate their genetic material, so they hijack the host cell's resources to do so.

Here's a breakdown of the actions viruses have on living cells:

1. Attachment and Entry:

* Attachment: Viruses bind to specific receptors on the surface of host cells. This is like a key fitting into a lock, ensuring the virus targets the correct cell type.

* Entry: Once attached, the virus enters the host cell. This can happen through:

* Fusion: The viral envelope merges with the cell membrane.

* Endocytosis: The cell engulfs the virus in a vesicle.

2. Replication and Assembly:

* Genome Replication: The virus releases its genetic material (DNA or RNA) into the host cell. This material then directs the cell's machinery to create more viral DNA or RNA.

* Protein Synthesis: The viral genome instructs the host cell to produce viral proteins, including capsid proteins (which form the protective shell) and enzymes necessary for replication.

* Assembly: New viral particles are assembled from newly produced viral proteins and nucleic acids.

3. Release:

* Lysis: Some viruses burst the host cell, releasing newly formed viral particles to infect other cells. This process is often destructive and can lead to cell death.

* Budding: Other viruses exit the cell by budding off from the cell membrane, taking a piece of the cell membrane with them as their envelope. This method is less destructive to the host cell, but can still lead to cell death over time.

Effects of Viral Infection:

* Disease: The disruption and destruction of cells by viruses can lead to a variety of diseases, ranging from mild colds to serious conditions like AIDS and Ebola.

* Immune Response: The host's immune system detects viral infection and mounts an immune response to eliminate the virus. This response can cause symptoms like fever, inflammation, and fatigue.

* Latency: Some viruses can remain dormant within the host cell without causing any symptoms. They can later reactivate, causing disease.

* Cancer: Some viruses can integrate their genetic material into the host cell's DNA, leading to uncontrolled cell growth and cancer.

It's important to note that viruses can have a variety of effects on living cells, depending on the specific virus and the host cell.