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Life Cycles of Pathogens

Life Cycles of Pathogens. The Basics of Viral Reproduction. All viruses reproduce via three basic steps: Viruses deliver their genetic material into a host cell. Viruses take over the host cell protein synthesis machinery to synthesize viral parts.

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Life Cycles of Pathogens

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  1. Life Cycles of Pathogens

  2. The Basics of Viral Reproduction • All viruses reproduce via three basic steps: • Viruses deliver their genetic material into a host cell. • Viruses take over the host cell protein synthesis machinery to synthesize viral parts. • Viral parts are assembled and exit host cells as new infectious particles. Read more at Suite101: Lysogenic Replication of Bacteriophage Viruses: Genetics & Reproduction of Hidden Virus through Lysogenyhttp://geneticsevolution.suite101.com/article.cfm/viral_lysogenic_replication#ixzz0f41ZlW8v

  3. The Lysogenic Cycle • The following are the steps of the lysogenic cycle:1) Viral genetic material (DNA or RNA) enters host cell2) Viral genetic material integrates into host cell DNA 3) Host cell copies viral chromosomes4) Host cell divides, and viral genes are transmitted to host daughter cells5) The virus is "triggered", the viral genetic material detaches from the host cell's DNA and enters the lytic cycle. • http://www.everythingbio.com

  4. Lysogenic Lytic The Lysogenic Reproductive Cycle of Bacteriophages Prophage

  5. Viral Triggers • While it is unclear as of yet what exactly constitutes a "trigger" that activates the viral DNA from the dormant stage, common stimuli include hormones, high stress levels (adrenaline), and free energy within the infected cell. • http://www.everythingbio.com

  6. Lytic Cycle • bacteriophages, viruses that have bacteria as hosts , reproduce via lytic replication, a type of viral replication that ultimately kills the infected bacterial cell. The five stages of the lytic cycle are as follows: Attachment: The phage encounters and connects to a bacterial cell. Entry: The phage injects its nucleic acid (genetic material) into the bacterium and destroys the bacterial DNA. Synthesis: No longer having its own DNA to work with, the bacterial cell begins replicating, transcribing and translating the viral nucleic acid. Assembly: The viral components made by the bacterial cell self-assemble into new viruses. Release: The bacterial cell is lysed (broken open), killing the cell and releasing the new viruses. Read more at Suite101: Lysogenic Replication of Bacteriophage Viruses: Genetics & Reproduction of Hidden Virus through Lysogeny • http://geneticsevolution.suite101.com/article.cfm/viral_lysogenic_replication Bacteriophage infecting a Bacterium Cell

  7. Attach Inject Replicate Release The Lytic Reproductive Cycle of Bacteriophages Virulent Phage

  8. Differences between . . . • Differences Between Lytic and Lysogenic Cycles • In the Lytic Cycle: • Viral DNA destroys Cell DNA, takes over cell functions and destroys the cell. • The Virus replicates and assembles new viruses • There are symptoms of viral infection. • Virulent viral infection takes place as new viruses infect other host cells. • In the Lysogenic Cycle: • Viral DNA merges with Cell DNA and does not destroy the cell, but becomes dormant. • The virus does not produce progeny. • There are no symptoms of viral infection. • Read more: http://www.brighthub.com/science/genetics/articles/30611.aspx#ixzz0e22HhvD6

  9. Herpes • An example of a virus that enter the lysogenic cycle is herpes, which first enters the lytic cycle after infecting a human, then the lysogenic cycle before travelling to the nervous system where it resides in the nerve fibers. After a long period of time (months to years) in a latent stage, the herpes virus is often reactivated to the lytic stage during which it causes severe nervous system damage. • http://www.everythingbio.com

  10. Retroviruses • the human immunodeficiency virus (HIV) has RNA for its genetic material but is able to enter the lysogenic cycle in host cells by changing into DNA • an enzyme called reverse transcriptase copies the RNA into DNA which is than able to integrate into the host DNA and become dormant for long periods of time before symptoms appear • HIV attacks helper T cells which are critical for initiating an immune response, so infection leaves the host with no way to fight the virus

  11. 4. Transcription and Translation 2. Reverse transcription 1. Building and entry 3. Integration 5. Assembly and Release The Reproductive Cycle of a Retrovirus—HIV Viral DNA Cell DNA Viral RNA and proteins Receptor

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