Infecting the Cell

Lytic Cycle Background:

The Lytic Cycle causes lysis of the host cell. Most viruses infect the host through the lytic cycle - a more efficient process.

After virus attachment and fusion, viruses release their genetic material into the cell. They interfere with normal cell activity through intercalating their own gene expression mechanisms with those of the host. By doing so, they manipulate the cell to (1) code for virus proteins, (2) replicate the viral genome, and facilitate the (3) assembly of new viruses. Once infection is complete, newly assembled viruses are released through lysis of the host cell.

STEPS:

1. Virus enters the cell.

2. Virus releases its genetic material (RNA or DNA) into the cell, and hijacks the host's cellular machinery.

3. The hijacked cell, unable to recognize the virus as a foreign pathogen, facilitates replication of the viral genome and synthesis of viral proteins. The cell's machinery (e.g. ribosomes) treats the viral genome as its own. It will replicate the genome and encode new envelope and capsid proteins. Virus replication and protein synthesis disrupts the process of normal protein synthesis processes that the cell carries out to maintain proper body function.

4. Viruses use a special mechanism to assemble the newly produced virus parts (including the envelope + capsid proteins and the genetic material) into new, whole viruses.

5. Once infection is complete, and viral load in the host cell is substantial, newly assembled viruses are released through lysis of the cell. Viruses enter the surrounding waters and continue infecting cells in the host organism.

6. Once the viral load is substantial, the host begins experiencing symptoms associated with the viral infection.

Other viruses will simply "bud" with the cell membrane, taking some of it when it exits the cell. This will allow the virus to look like another normal cell. (ADD THIS?)

• ScienceDirect. "Lytic Cycle," https://www.sciencedirect.com/topics/immunology-and-microbiology/lytic-cycle
• Khan Academy. "Bacteriophages," https://www.khanacademy.org/science/biology/biology-of-viruses/virus-biology/a/bacteriophages

Lysogenic Cycle Background:

The Lysogenic Cycle allows viruses to reproduce without killing the host. It involves a period of initial dormancy before the virus hijacks the cell's machinery to reproduce.

After virus attachment and fusion, viruses release their genetic material into the cell. However, once the virus' genetic material is inside the cell, it is not immediately encoded by the cell. Instead, it recombines with the host cell's genetic material, remaining dormant/non-active. Once the virus' dormant genetic material is activated by an environmental trigger, it enters the lytic cycle and thus begins interfering with cellular mechanisms. Herpesvirus (a DNA virus), HIV (human immunodeficiency virus), and some DNA bacteriophages follow the lysogenic cycle. IS THIS ACCURATE? - Most RNA viruses, with the exception of reverse-transcribing viruses, do not follow the lysogenic cycle because their RNA genome cannot integrate with the host cell's DNA.

STEPS:

1. Virus enters the cell.

2. Virus releases its genetic material (RNA or DNA) into the cell.

3. The virus' genetic material recombines with the host cell's genetic material, remaining dormant/non-active. The recombined virus is called a provirus.

4. The host's cell's continue normal cell division, but create identical cells all containing the provirus.

5. Under the right conditions, the dormant provirus is activated. It exists the cell's DNA and enters the lytic cycle and thus begins utilizing the cell's machinery to replicate.

6. The lytic cycle begins.

• Khan Academy. "Bacteriophages," https://www.khanacademy.org/science/biology/biology-of-viruses/virus-biology/a/bacteriophages