Compare lysogeny and lytic cycle of bacteriophages.
Answers
Phage have a very simple structure (Figure 1). Their genetic material is contained in a prism shaped head, surrounded by a protein capsid. This is connected to the elongated sheath (sometimes called the tail) by a neck or collar region.
The sheath forms a hollow tube through which the viral DNA/RNA is injected into the host cell and is surrounded by protective sheath proteins. At the bottom of the sheath is the base plate to which the tail fibers (normally six) that facilitate attachment to the host cell are attached.
bodyText
Figure 1. Example structure of a bacteriophage.
In order to reproduce, phage must first enter the host cell. They bind to specific receptors on the bacterial cell surface with their tail fibers (adsorption) and create a hole, a process which, along with attachment, is coordinated by the base plate3. A rigid tube is propelled out of the sheath, puncturing a hole in the bacterial cell membrane through which they inject their genetic material (DNA or RNA, double or single stranded). They can then hijack the host cell’s cellular machinery for their own replication if surrounding conditions are unfavorable in a process called the lytic cycle. Alternatively, they may enter a dormant state, known as the lysogenic cycle, within the host cell if conditions are favorable.
