Lytic vs Lysogenic cycle |12 Differences in Points
The virus undergoes multiplication inside the cells of a host. Of them, bacteriophages show two types of reproduction in their life cycle.
1. Lytic cycle.
2. Lysogenic cycle.
Lytic vs Lysogenic cycle
|Sl.No||Lytic cycle||Lysogenic cycle|
|1||Lysis means destruction. A Lytic cycle will lead to the destruction of the infected cell and hence the name.||In lysogeny, integration of DNA occurs.|
|2||The virus get multiplied inside the bacterial host and releases when cell destroys.||In lysogeny, the virus multiply by usual prokaryotic reproduction|
|3||Bacteriophages that undergo lytic cycle|
are virulent type.
|Bacteriophages that undergo lysogenic cell are non-virulent or temperate.|
|4||Host cells undergo lysis.||The host cell do not undergo lysis.|
|5||Multiplies in short duration||Takes time to multiply|
|6||The host DNA gets hydrolyzed.||The host DNA is not hydrolyzed.|
|7||There is no integration of viral DNA with that of the host||Integration of DNA with the host DNA is seen.|
|8||The symptoms are evident in lytic cycle.||The symptoms are not evident in lysogenic cycle.|
|9||Gene recombination of the host DNA is|
|Gene recombination of the host DNA is allowed.|
|10||Cellular function of the host cell is|
completely taken under control by the
|Cellular function of the host is parially controlled by the virus.|
|11||There is no formation of prophage.||Formation of prophage occurs.|
|12||Lytic cycle occurs through the following steps.|
4. Assembly & release
|Some phages encodes a repressor protein in bacterial host which inhibits lytic cycle. In such cases lysogenic cycle occurs. Lysogenic cycle comprises of following|
4. Spontaneous induction
5. Assembly & release
|13||The number of phages formed is less number.||The number of phages formed is profuse and high in number.|
The stages of lytic cycle is as follows
1. Adsorption: Tip of the phages’ tail attached to the cell surface of the host via specific receptor sites.The host which lacks the receptor is resistant to the phage infection. After adsorption the sheath of the phage becomes short and wide.
2. Penetration: Penetration of phage DNA is mechanical. Binding to the host cells occurs due to electrostatic interactions which are influenced by Mg 2+ and Ca 2+ . Enzymes like lysozyme and endolysin protein attacks the peptidoglycan of bacteria and digest it. cell wall is also digested by viral activation of host degradation enzymes. The head and tail remains outside after the penetration of phage DNA.
3. Transcription / Replication and maturation:
This process occurs in several steps. Immediate early, delayed early and late
gene products are produced. Immediate early gene transcribe using
RNA polymerase. It codes for nucleases (breaks host DNA) and enzymes (alter bacterial RNA polymerase to transcribe delayed early phage genes).
Delayed early gene codes for polymerases, ligases, phage enzymes
which produce phage DNA constituents like 5- hydroxymethylcytosines (it replaces bacterial cytosine), glycosylating enzymes and enzymes which destroy precursors of cytosine deoxynucleotides. Late gene code for lysozyme, structural components like head, tail and fibers.
Synthesis of host mRNA and thereby the protein formation is stopped.
Host DNA is degraded into small fragments. Nucleoid region of the host is
dispersed. During this process, phage mRNA is produced which codes the production of capsids, virion specific proteins etc. Time when the number of phages increases is called a rise period.
Assembly and release: Formed phage components assemble together to a mature phage and get released by the rupture of the host cell. Time from infection to lysis is called a latent period.
Adsorption: This step shows similar mechanism of
adsorption of lytic cycle.
Penetration: Penetration is also similar in both the reproductive cycles.
After penetration, phages could not be recovered and this period is called a
eclipse period (in both cycles).
Prophage formation: Phage DNA gets integrated into host DNA is called as prophage. This prophage (behaves as a plasmid) in the host chromosomes acts as a gene. When the host replicates and divides, the prophage replicates along with it and gets transmitted to the daughter cells.
Spontaneous induction: The process of separation of prophage from the host chromosome is called as spontaneous induction. When the prophage containing host cell is exposed to UV radiation, heat, stress or some chemicals; the prophage gets excised from the bacterial chromosome.
The induction is followed by replication, maturation, assembly and release of the phage as in lytic cell.
Assembly and release :This step is similar to the assembly and
release of phages in lytic cycle.