Difference Between Lytic Cycle and Lysogenic Cycle

Main Difference – Lytic Cycle vs Lysogenic Cycle

A virus is an infectious agent that comprises a nucleic acid molecule inside a protein coat. Viruses may infect animal, plant, bacterial or algal cells. Once infected, viruses can reproduce inside the host. Thousands of identical copies from the original virus may be produced by the host cell in an extraordinary rate.  Lytic cycle and the lysogenic cycle are two mechanisms of viral replication, which may occur interchangeably. The main difference between lytic cycle and lysogenic cycle is that lytic cycle destroys the host cell whereas lysogenic cycle does not destroy the host cell. Viral DNA destroys the host cell DNA and arrests the cell functions in the lytic cycle. However, in the lysogenic cycle, viral DNA may merge with the host DNA.

Key Areas Covered

1. What is Lytic Cycle
      – Definition, Mechanism, Role
2. What is Lysogenic Cycle
      – Definition, Mechanism, Role
3. What are the Similarities Between Lytic Cycle and Lysogenic Cycle
      – Outline of Common Features
4. What is the Difference Between Lytic and Lysogenic Cycle
      – Comparison of Key Differences

Key Terms: Cell Lysis, Host Cell, Lysogenic Cycle, Lytic Cycle, Viral DNA, Viral Reproduction

What is Lytic Cycle

Lytic cycle is a type of a viral reproduction mechanism which results in the lysis of the infected cell. It occurs through five stages: adsorption, penetration, replication, maturation, and release. Virus may attach to the cell wall or the plasma membrane of the host cell. The attachment of the virus occurs to a specific receptor of the cell membrane, weakening the cell membrane. Virus produces a hole to penetrate its genetic material into the cytoplasm of the host. If the virus enters a permissive host, the viral DNA is replicated and produces viral proteins inside the host cell. Then, new viral particles are produced by the maturation of the proteins. The lysis of the host cell releases the viral particle from the cell. The steps of the lytic cycle are shown in figure 1.

Figure 1: Lytic Cycle

Since a new viral progeny is released to the outside, the lytic cycle is considered as the major mechanism of viral replication. 100-200 viral particles are produced per cycle. The lysis of the host is achieved by the enzyme released by the virus. On that account, the lytic viruses hijack the cellular mechanisms of the infected cell. The lysis of the cells produces symptoms of the viral infection in the host. 

What is Lysogenic Cycle

Lysogenic cycle is a viral reproduction mechanism in which the viral DNA is integrated into the host genome. The new set of genes in the host genome is called the prophage. Thereby, viral DNA becomes a part of the host genome. Once the host genome replicates, the viral genes are also replicated simultaneously. The prophage stage is shown in figure 2.

Figure 2: Prophage

Since no new progeny is produced by the lysogenic cycle, the host cell does not lyse. Therefore, no symptoms of the viral infection are shown in the host. Some viruses first undergo lysogenic cycle and then enters the lytic cycle. 

Similarities Between Lytic Cycle and Lysogenic Cycle

• Both lytic cycle and lysogenic cycle are mechanisms of viral reproduction.
• Both lytic cycle and lysogenic cycle only occur inside a host cell.
• Both lytic cycle and lysogenic cycle may produce thousands of original copies of the original virus.
• Both lytic cycle and lysogenic cycle moderate the DNA replication and protein synthesis of the host cell.

Difference Between Lytic Cycle and Lysogenic Cycle

Definition

Lytic Cycle: Lytic cycle is a type of a viral reproduction mechanism, which results in the lysis of the infected cell.

Lysogenic Cycle: Lysogenic cycle is a viral reproduction mechanism where the viral DNA is integrated into the host genome.

Integration of the Viral DNA

Lytic Cycle: In the lytic cycle, viral DNA does not integrate into the host DNA.

Lysogenic Cycle: In the lysogenic cycle, viral DNA integrates into the host DNA.

Prophage Stage

Lytic Cycle: Lytic cycle does not have a prophage stage.

Lysogenic Cycle: Lysogenic cycle has a prophage stage.

Host DNA

Lytic Cycle: Host DNA is hydrolyzed during the lytic cycle.

Lysogenic Cycle: Host DNA is not hydrolyzed during the lysogenic cycle.

Viral DNA Replication

Lytic Cycle: Viral DNA replication occurs independently from the host’s DNA replication in the lytic cycle.

Lysogenic Cycle: Viral DNA replication occurs along with the host’s DNA replication in the lysogenic cycle.

Productivity of Viral DNA

Lytic Cycle: The productivity of viral DNA in the lytic cycle is high due to the independent replication of the viral DNA.

Lysogenic Cycle: The productivity of the viral DNA in lysogenic cycle is lower than that of the lytic cycle since the viral replication occurs along with the host’s DNA replication.

Host’s Cellular Mechanisms

Lytic Cycle: Host’s cellular mechanism is completely taken over by the viral genome in the lytic cycle.

Lysogenic Cycle: Host’s cellular mechanism is slightly disturbed by the viral genome in the lysogenic cycle.

Virulency

Lytic Cycle: The lytic virus is virulent.

Lysogenic Cycle: The lysogenic virus is non virulent.

Lysis of the Host Cell

Lytic Cycle: Host cell is lysed during the release of the viral particles in the lytic cycle.

Lysogenic Cycle: Host cell is not lysed by the lysogenic cycle.

Liberation of the Viral Particles or a Progeny

Lytic Cycle: Viral particles are liberated in the lytic cycle. Therefore, lytic cycle produces a progeny of virus.

Lysogenic Cycle: Typically, viral particles are not liberated in the lysogenic cycle. Therefore, the lysogenic cycle does not produce a viral progeny.

Time

Lytic Cycle: Lytic cycle occurs within a short period of time.

Lysogenic Cycle: Lysogenic cycle takes time.

Follow up

Lytic Cycle: Lytic cycle cannot follow the lysogenic cycle.

Lysogenic Cycle: Lysogenic cycle can follow the lytic cycle.

Symptoms of Viral Infection

Lytic Cycle: Lytic cycle shows the symptoms of viral replication.

Lysogenic Cycle: Lysogenic cycle does not show symptoms of viral replication.

Genetic Recombination in Bacteria

Lytic Cycle: Lytic cycle does not allow genetic recombination in the host bacterium.

Lysogenic Cycle: Lysogenic cycle allows genetic recombination of the host bacterium.

Conclusion

Lytic cycle and lysogenic cycle are two mechanisms of the viral reproduction. In the lytic cycle, the host cell is lysed by the release of the new progeny of the virus. However, no cell lysis occurs in the lysogenic cycle. The viral DNA is integrated into the host genome in the lysogenic cycle. The main difference between lytic cycle and lysogenic cycle is the influence of each type of reproductive cycle to the host cell.

Reference:

1. “Lysogenic Cycle – Definition and Steps.” Biology Dictionary, 28 Apr. 2017, Available here.
2.“Lytic Cycle of a Virus: Definition & Steps.” Study.com, Available here

Image Courtesy:

1. “Lytic Cycle” by xxoverflowed (CC BY 2.0) via Flickr
2. “Prophage SVG” By Prophage.JPG: Suly12derivative work: Asiela (talk) – Prophage.JPG (CC BY-SA 3.0) via Commons Wikimedia

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