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Viral Reproductive

Cycles

II-Dahlia

Group 6 & Group 8

Lytic CycleLysogenic Cycle

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How do viruses reproduce?

Viruses invade or infect a living host cell inorder to replicate.

Either by

Lytic Cycle

Lysogenic Cycle

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Lytic Cycle

Lytic cycle of T4 phage on an E. Colicell.

A phagereproductive cyclePhage- bacterial

viruses.

Culminates in thedeath of the hostcell

Virluent phage-phage reproducingonly by lytic cycle

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Lytic Cycle

1. Attachment

Molecules on its tail fibersattach to the surface of thebacterium.

2. Penetration

The sheath of its tailcontracts, injecting DNAinto the cell.

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Lytic Cycle

3. Synthesis of viral genomes and proteins.

The phage DNA directsthe production of proteinsand copies of its genome.

4. Assembly

Three sets of proteinsassemble to form heads,tails, and tail fibers. Thephage genome is packed

inside the capsid.

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Lytic Cycle

5. Release

Phage produces enzyme that damagesthe bacterial cell wall, allowing fluid toenter until the cell swells and bursts.

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Lysogenic Cycle

Allows replication of the phage genome withoutdestroying the host

Phage genome is stored in the DNA of the hostand can be passed to many generations.

Temperate phage- phage capable of usingeither cycles

Ex. (lambda) phage- resembles T4 but hasonly one, short tail fiber.

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Lysogenic Cycle

Lytic cycle of a phage

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Lysogenic Cycle

Stages 1 & 2 of lytic cycle

The cycle undergoes attachment of thevirus and penetration of its genome to intothe host cell.

3.The phages DNA integrates into thebacterial chromosome andbecomes a prophage.

Prophage phage genome

integrated into the hosts DNAchromosome

Can be caused by starvationand low temperature.

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Lysogenic Cycle

4. The bacterium reproducesnormally, replicating theprophage as well andpassing it to its daughtercells.

5. Spontaneous induction

After generations, a

prophage finally initiatesexit from the bacterialchromosome.

Increased growth rate, less repressor genes, possibility for induction

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Lysogenic Cycle

6. The rest of the stages in thelytic cycle will occur.

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References

Main reference

Miller, K.R. and Levine, J. (1995). Biology. EnglewoodCliffs, New Jersey: Prentice-Hall, Inc.

Other references

Cambell, N.A. and Reece, J.B. (2007). Biology(7

th

ed.). Menlo Park, California: Benjamin Cummings.

Keiser, G.E. (2011, March). The Lysogenic Life Cycle.Retrieved fromhttp://faculty.ccbcmd.edu/courses/bio141/lecguide/unit3/viruses/lysolc.html

Keiser, G.E. (2011, March). The Lytic Life Cycle.Retrieved fromhttp://faculty.ccbcmd.edu/courses/bio141/lecguide/uni

t3/viruses/lytlc.html

http://faculty.ccbcmd.edu/courses/bio141/lecguide/unit3/viruses/lysolc.htmlhttp://faculty.ccbcmd.edu/courses/bio141/lecguide/unit3/viruses/lysolc.htmlhttp://faculty.ccbcmd.edu/courses/bio141/lecguide/unit3/viruses/lytlc.htmlhttp://faculty.ccbcmd.edu/courses/bio141/lecguide/unit3/viruses/lytlc.htmlhttp://faculty.ccbcmd.edu/courses/bio141/lecguide/unit3/viruses/lytlc.htmlhttp://faculty.ccbcmd.edu/courses/bio141/lecguide/unit3/viruses/lytlc.htmlhttp://faculty.ccbcmd.edu/courses/bio141/lecguide/unit3/viruses/lysolc.htmlhttp://faculty.ccbcmd.edu/courses/bio141/lecguide/unit3/viruses/lysolc.html

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Images

Slide 3, 5, & 8 bio3400.nicerweb.net

Slides 4, 5, 6, 9, 10, 11, &12 http://faculty.ccbcmd.edu/courses/bio141/lecguide/unit3/viruses/lysolc.html

http://faculty.ccbcmd.edu/courses/bio141/lecguide/unit3/viruses/lytlc.html

Czyz, A., Los, M., Wrobel, B., Wegrzyn, G. (2001,

April 18). Inhibition of spontaneous induction oflambdoid prophages in Escherichia colicultures. BMCBiotechnology, 1. doi:10.1186/1472-6750-1-1

http://faculty.ccbcmd.edu/courses/bio141/lecguide/unit3/viruses/lysolc.htmlhttp://faculty.ccbcmd.edu/courses/bio141/lecguide/unit3/viruses/lytlc.htmlhttp://faculty.ccbcmd.edu/courses/bio141/lecguide/unit3/viruses/lytlc.htmlhttp://faculty.ccbcmd.edu/courses/bio141/lecguide/unit3/viruses/lysolc.html