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8 Cards in this Set
- Front
- Back
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Bacteriophages undergo different types of cylces. Name these cycles
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Lytic cycle and lysogenic cycle
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What does the word "lyse" mean?
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Burst (explode): This is what happens to the host cell in the lytic cycle
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There are two stages in the lytic cycle or a virus. What are they?
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Early stage and late stage
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Explain exactly what is happneing in the lytic stage.
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1. A virus infects a host cell and injects its DNA into it.
2. The host's own RNA polymerase binds to the virus' DNA at the promoter site. 3. The viral genes are transcribed 4. Three proteins are made: one shuts down the host's gene transcription, the second stimulates viral replication and the third assists in the "late stage" of the cycle 5. Viral enzymes digest (kill) the host's chromosomes which provide nucleotides for further synthesis. |
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Explain exaclty what is happening in the late lytic stage.
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1. The third protein from the early cycle begins to stimulate viral gene transcription
2. These genes encode the capsid (virus head) and speacil enzymes that aid in "exploding" the cell 3. The host cell eventually explodes, releasing all of the new virons |
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This is a diagram of both the early and late stages of the lytic cycle.
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Study diagram
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Explain in detail the lysogenic cycle.
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1. Lysogeny postpones the lytic cyle for the sole purpose of replicating "silently" until the time is "just right" to perform the lytic cycle
2. The virus injects its DNA into the host 3. This DNA integrates itself into the host's chomosomes becoming a PROPHAGE 4. The host cell divides - the viral DNA is replicated |
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Explain what takes place when (and why) a host cell transitions from the lysogenic cycle to the lytic cycle.
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1. If the lysogenic cycle cell is not growing well, it "cuts its loses" and enters the lytic cycle
2. If growing rapidly, the regulatory protein "cl" attaches to a special promoter that REPRESSES the lytic cycle (and will therefore remain in the lysogenic cycle) 3. However, if the cell is not growing rapidly, the protein "Cro" attaches to a different promoter which ACTIVATES the lytic cycle 4. This process is litteraly a "switch": if one promoter is activated, then the other is turned off. |
