lytic and lysogenic cycles

lysogenic cycle

The Lysogenic Cycle is another type of viral reproductive cycle in which the genome of the phage is replicated without destroying the host. Phages capable of using both modes of reproduction (lytic and lysogenic) are referred to as TEMPERATE PHAGES.

assembly

* newly produced viral components are assembled into complete new virus particles

lysis and release

* the host cell bursts open and releases new virus particles * these particles begin another cycle by infecting nearby cells

attachment

* virus attaches to a host cell * locks on to a specific receptor on the surface of the host cell (lock and key)

entry

* virus injects its DNA into the host cell * the empty coat remains outside the host cell * inside the cell, the viral DNA breaks down the host cell DNA

replication

* virus takes over total metabolic activities of the host cell * using the raw materials in the cell, viral DNA directs production of new virus parts

stages of lytic cycle

1. Attachment 2. Entry 3. Replication 4. Assembly 5. Lysis

lytic cycle

The LYTIC CYCLE is a viral reproductive cycle, during which a virus takes over all metabolic activities of a cell and causes the host cell to die. Bacteriophages that ONLY reproduce using the lytic cycle are called a VIRULENT PHAGES.

during the lysogenic cycle the phage genome is almost silent within the bacteria. why?

When the viral DNA is incorporated into the host cell's chromosome, the viral DNA is referred to as a PROPHAGE. One gene on the prophage codes for a protein that prevents transcription of most of the other prophage genes. This explains why the phage genome is mostly silent, but this also explains why the viral DNA does not direct production of more virus, which eventually prevents the cell from lysing or breaking in the lysogenic cycle.

what determines wether or not the lytic or lysogenic cycle is entered?

receptors on the membrane. The term "lysogenic" implies that prophages are capable of giving rise to active phages that lyse their host cells. This occurs when the viral genome exits the bacterial chromosome and initiates the lytic cycle. The triggers for this switch-over are usually environmental factors such as mutagens (e.g. radiation and presence of certain chemicals)