Viruses, lytic and lysogenic cycles

lysogenic cycle

The Lysogenic Cycle is another type of viral reproductive cycle in which the genome of the phage is replicated without destroying the host. Phages capable of using both modes of reproduction (lytic and lysogenic) are referred to as TEMPERATE PHAGES.

Virology

the study of viruses and viral diseases

Viral Biosynthesis

Parts of the virus are made.

assembly

* newly produced viral components are assembled into complete new virus particles

lysis and release

* the host cell bursts open and releases new virus particles * these particles begin another cycle by infecting nearby cells

attachment

* virus attaches to a host cell * locks on to a specific receptor on the surface of the host cell (lock and key)

entry

* virus injects its DNA into the host cell * the empty coat remains outside the host cell * inside the cell, the viral DNA breaks down the host cell DNA

replication

* virus takes over total metabolic activities of the host cell * using the raw materials in the cell, viral DNA directs production of new virus parts

stages of lytic cycle

1. Attachment 2. Entry 3. Replication 4. Assembly 5. Lysis

Viral Trigger

A condition in the host cell causes the viral DNA to activate into the lytic cycle. This can be caused by hormones or physical factors.

Lysogenic Cycle

A phage replication cycle in which the viral genome becomes incorporated into the bacterial host chromosome as a prophage and does not kill the host.

Viral Maturation

A process that takes place after separation of the viral infectious particle from host cell by budding or sealing of spherical capsid.

Virus

A tiny, nonliving particle that invades and then reproduces inside a living cell.

Lytic Cycle

A type of viral (phage) replication cycle resulting in the release of new phages by lysis (and death) of the host cell.

Herpes

A viral infection causing small painful blisters and inflammation, most commonly at the junction of skin and mucous membrane in the mouth or nose or in the genitals.

HIV

A virus that attacks and destroys the human immune system.

Bacteriophage

A virus that infects bacteria

lytic cycle

The LYTIC CYCLE is a viral reproductive cycle, during which a virus takes over all metabolic activities of a cell and causes the host cell to die. Bacteriophages that ONLY reproduce using the lytic cycle are called a VIRULENT PHAGES.

Viral Assembly

Genetic material surrounded by a protein coat

Viral Sheath

Helps inject the DNA

HPV

Human Papillomavirus

Host Cell

Living cell in which a virus can actively multiply or in which a virus can hide until activated by environmental stimuli

Viral DNA

Nucleic acid that contains the information for reproducing the virus

Capsid

Outer protein coat of a virus.

Viral Duplication

The viral DNA hides in the host DNA and replicates with the host in stealth.

Viral Attachment

This occurs when the virus attaches to its host. This is the moment in which the virus recognizes the host as a cell to infect and will inject viral DNA or RNA into the host.

Viral Penetration

Viral genetic material enters host cell

Viral Lysis

When a viral infected cell bursts and releases large amounts of organic matter.

during the lysogenic cycle the phage genome is almost silent within the bacteria. why?

When the viral DNA is incorporated into the host cell's chromosome, the viral DNA is referred to as a PROPHAGE. One gene on the prophage codes for a protein that prevents transcription of most of the other prophage genes. This explains why the phage genome is mostly silent, but this also explains why the viral DNA does not direct production of more virus, which eventually prevents the cell from lysing or breaking in the lysogenic cycle.

what determines wether or not the lytic or lysogenic cycle is entered?

receptors on the membrane. The term "lysogenic" implies that prophages are capable of giving rise to active phages that lyse their host cells. This occurs when the viral genome exits the bacterial chromosome and initiates the lytic cycle. The triggers for this switch-over are usually environmental factors such as mutagens (e.g. radiation and presence of certain chemicals)