Viral Life Cycle of the Bacteriophage

What are the two life cycles seen in a bacteriophage?

A lytic or lysogenic cycle:

• Lytic, coming from the same stem word for lysis, means to cut/split. When a bacteriophage infects a bacterium on a lytic mission, the host cell machinery is used to produce bacteriophage components. Once a critical mass is attained, the bacterial cytosol is filled with bacteriophages and the host cell is sacrificed as it spills open and releases phages into the environment.
• Lysogenic cycles are much less barbaric. Here, the bacteriophage integrates itself into the bacterial genome. When this occurs, the bacteriophage is called a provirus and it is replicated with each generation of bacteria. This can occur indefinitely or be triggered to cause the bacteriophage to enter a lytic cycle.

Why are viruses obligate intracellular parasites?

Viruses do not have the machinery to replicate without a host. In the case of bacteriophages, the host is a bacteria, e.g. $E. \ coli$, and the bacterial ribosomes and machinery are used to generate the parts to produce progeny viruses.

What are the steps of viral infection (on a cellular level)?

1. Attachment
2. Injection
3. Replication
4. Expression
5. Assembly
6. Release

What makes the life cycle of retroviruses unique?

Retroviruses have an RNA genome that uses a $reverse \ transcriptase$ to turn the genome into DNA (unique among viruses). The DNA genome then integrates into the host's genome (common among viruses).