Made by:

Group 7 II – Jasmin

Jerome Añano

Joshua Tsang

Zel Santamaria

Lytic Cycle

Lytic cycle is the process in which a host cell is invaded, lysed, and destroyed by a virus.[1]

The lytic cycle definition states that the virulent phages are those phages that can multiply only on bacterial cells. At the end of their life cycle, they cause cell lysis that kills the host bacteria. The viruses that infect bacteria are called bacteriophages.[2]

What is Lytic Cycle?

Example: T4 Bacteriophage

Bacteriophage

Bacteriophages are viruses that can infect and destroy bacteria. This fact was actually used, prior to the discovery and widespread use of antibiotics, to treat certain infections. 

Who discovered bacteriophages is the subject of debate. Most credit Frederick Twort (1915), an English bacteriologist, and Felix d'Herelle (1917), a French-Canadian microbiologist with the independent discovery of bacteriophages.

Application / Significance

Felix D'Herelle

Frederick Twort

There are 6 steps in the lytic cycle:1. Phage attaches to a specific host bacterium.2. Phage injects its DNA.3. Disrupts the bacterial genome and kills the

bacterium.4. Takes over the bacterial DNA and protein

synthesis machinery to make phage parts.5. Assembly of new phages.6. The lysis of the bacterial cell wall to release a

hundred new copies of the input phage into the environment.[3]

The Lytic Cycle

The Lytic Cycle

The Lytic Cycle

The Lytic CycleThe general life cycle of a lytic virus, from infection of the host cell, hijacking of the host cells mechanisms, use of the host cells mechanisms to produce viral components, and assembly of the components into progeny viruses, to the destruction of the host cell by rupturing its plasma membrane (lysis) and the release of the progeny viruses so that they can spread and infect other cells.[4]

The burst time is calculated from the time the phage is attached to the cell till the lysis of the host cell and release of new phages. The total burst time is about 20 to 40 minutes. The number of viruses that are released from the cell at the burst time is called burst size. The burst size can vary from 50 to 200 phages. This was all about the lytic cycle of bacteriophage. The lytic cycle leads to cell lysis, hence the name.[5]

The Lytic Cycle

The lytic cycle of the bacteriophage: a lunar analogy

1) The bacteriophage does a lunar landing…

2) …and injects its DNA…

3)… which codes for the protein-bits of the bacteriophage…

4) …that assemble into new bacteriophages…

5) …and the moon-cell explodes.

6) Bacteriophages now free to wreak havoc on the entire universe!!

vs.

In the Lytic Cycle:

Viral DNA destroys Cell DNA, takes over cell functions

and destroys the cell.The Virus replicates and produces progeny

phages.There are symptoms of viral infection.Virtulant viral infection takes place.

Lytic Cycle vs. Lysogenic Cycle

In the Lysogenic Cycle:

Viral DNA merges with Cell DNA and does not destroy

the cell.The Virus does not produce progeny.There are no symptoms of viral infection.Temperate viral replication takes place.

Lytic Cycle vs. Lysogenic Cycle

TabulatingLytic Cycle Lysogenic Cycle

The lytic cycle causes the host bacterium to undergo cell lysis, that is, cell destruction.

The lysogenic cycle does not cause cell lysis or cell destruction.

The lytic cycle can lead to production of 100 to 200 progeny phages.

The DNA of the phage gets integrated into the bacterial chromosome and no progeny are produced mostly.

Lytic cycle cannot be converted into the lysogenic cycle.

Lysogenic cycle can be converted into lysogenic cycle when the host cell is exposed to chemical or physical agents.

Lytic Cycle vs Lysogenic Cycle

1. Miller, Levine, (2000). BIOLOGY. New Jersey: Prentice Hall 2. What is Lytic Cycle. October 2, 2011, from

http://www.buzzle.com 3. Lytic Cycle. October 2, 2011, from http://www.creationwiki.org 4. Lytic Cycle. October 2, 2011, from http://www.lexic.us 5. What is Lytic Cycle? . October 2, 2011, from http://

www.answers.com http://pudsandlosers.blogspot.com/2009_11_29_archive.html http://www.brighthub.com/science/genetics/articles/

30611.aspx#ixzz1aTCdeuwr http://www.scq.ubc.ca/doodling-drooling-macrophages/ http://www.buzzle.com/articles/lytic-cycle-vs-lysogenic-cycle.html http://en.wikipedia.org/wiki/Lytic_cycle http://en.wikipedia.org/wiki/Lysogenic_cycle

Bibliography

Thank you for listening