1. Life Cycles of Viruses

2. Two Cycles and A Bit of Review
Remember that viruses are not able to reproduce on their own. They rely on a ‘host cell’ for reproduction
In the Lytic Cycle viruses infect the host cell, use it to replicate and then destroy it
In the Lysogenic Cycle the virus infects the host cell and inserts its DNA into the DNA of the host cell.

3. The Lytic Cycle
Proteins on the surface of the virus bind with proteins on the surface of the host cell  this is specificity
The Virus injects its DNA into the host cell
The DNA from the virus shuts down and takes over the host cell
The virus uses the materials of the host cell to make thousands of copies of its own protein coat and DNA

4. The Lytic Cycle
5. The cell lyses (bursts) and the releases hundreds of virus particles
This process is called a lytic infection

5. The Lysogenic Cycle
Proteins on the surface of the virus bind with proteins on the surface of the host cell  this is specificity
The Virus injects its DNA into the host cell
The viral DNA is inserted into the host cell’s DNA
The viral DNA is now known as a prophage

6. The prophage may remain as part of the host cell for many generations
The inserted DNA may be useful. It can block other viruses from entering the cell or create useful proteins
Eventually the viral DNA removes itself from the DNA of the host cell and start reproducing viruses

7. RETROVIRUSES Retroviruses contain RNA
They produce a DNA copy of their genes when they enter the cell
This DNA is entered into the host cell’s DNA
The DNA is then replicated and passed on to daughter cells each time the host cell divides