Lysogenic cycle

Not to be confused with Lytic cycle.
Lysogenic cycle, compared to lytic cycle
Lysogenic Cycle:1. The prokaryotic cell is shown with its DNA, in green. 2. The bacteriophage attaches and releases its DNA, shown in red, into the prokaryotic cell. 3. The phage DNA then moves through the cell to the host's DNA. 4. The phage DNA integrates itself into the host cell's DNA, creating prophage. 5. The prophage then remains dormant until the host cell divides. 6. After the host cell has divided, the phage DNA in the daughter cells activate, and the phage DNA begins to express itself. Some of the cells containing the prophage go on to create new phages which will move on to infect other cells.

Lysogeny, or the lysogenic cycle, is one of two cycles of viral reproduction (the lytic cycle being the other). Lysogeny is characterized by integration of the bacteriophage nucleic acid into the host bacterium's genome or formation of a circular replicon in the bacterial cytoplasm. In this condition the bacterium continues to live and reproduce normally, while the bacteriophage lies in a dormant state in the host cell. The genetic material of the bacteriophage, called a prophage, can be transmitted to daughter cells at each subsequent cell division, and later events (such as UV radiation or the presence of certain chemicals) can release it, causing proliferation of new phages via the lytic cycle.[1]

Lysogenic cycles can also occur in eukaryotes, although the method of DNA incorporation is not fully understood. For instance, the HIV viruses can either infect humans lytically, or lay dormant (lysogenic) as part of the infected cells' genome, keeping the ability to return to lysis at a later time.[2]

The difference between lysogenic and lytic cycles is that, in lysogenic cycles, the spread of the viral DNA occurs through the usual prokaryotic reproduction, whereas a lytic cycle is more immediate in that it results in many copies of the virus being created very quickly and the cell is destroyed. One key difference between the lytic cycle and the lysogenic cycle is that the latter does not lyse the host cell straight away.[3] Phages that replicate only via the lytic cycle are known as virulent phages while phages that replicate using both lytic and lysogenic cycles are known as temperate phages.[1]

In the lysogenic cycle, the phage DNA first integrates into the bacterial chromosome to produce the prophage. When the bacterium reproduces, the prophage is also copied and is present in each of the daughter cells. The daughter cells can continue to replicate with the prophage present or the prophage can exit the bacterial chromosome to initiate the lytic cycle.[1] In the lysogenic cycle the host DNA is not hydrolyzed but in the lytic cycle the host DNA is hydrolyzed in the lytic phase.

  1. ^ a b c Campbell, Neil A.; Reece, Jane B. (2005). Biology. San Francisco: Pearson. pp. 338–339. ISBN 9780805371710.
  2. ^ Zheng, Yong-Hui; Lovsin, Nika; Peterlin, B. Matija (2005-03-15). "Newly identified host factors modulate HIV replication". Immunology Letters. 97 (2): 225–234. doi:10.1016/j.imlet.2004.11.026. ISSN 0165-2478. PMID 15752562.
  3. ^ Lodish, Harvey F. (2007). Molecular Cell Biology. New York: W.H. Freeman. pp. 158–159. ISBN 9780716776017.