In the following diagram of lytic and lysogenic cycles, describe ... - Free Printable

This image illustrates the two main life cycles of bacteriophages (viruses that infect bacteria): the Lytic Cycle and the Lysogenic Cycle. The task is to identify the labeled parts and steps in these cycles.

I will solve this by first identifying the key components and then describing each step of both cycles based on biological knowledge.

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Step 1: Identify the Key Components

The diagram shows a bacteriophage (virus) and a bacterial cell. I need to label the parts of the bacteriophage and the stages of infection.

- a. Points to the head/capsid of the bacteriophage, which contains the viral DNA.
- b. Points to the tail fibers, which help the phage attach to the bacterial cell.
- c. Points to the newly assembled bacteriophages inside the lysed bacterial cell.
- d. Points to the prophage, which is the viral DNA integrated into the bacterial chromosome during the lysogenic cycle.
- e. Points to the bacterial chromosome with the integrated prophage.

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Step 2: Describe the Lytic Cycle (Left Side)

The lytic cycle results in the destruction (lysis) of the host bacterium.

1. Attachment (Step 1): The bacteriophage attaches to the surface of the bacterial cell using its tail fibers (b).
2. Penetration (Step 2): The phage injects its DNA (from part a) into the bacterial cell. The empty capsid remains outside.
3. Biosynthesis (Step 3): The viral DNA takes over the bacterial machinery to replicate itself and synthesize new viral proteins. New phage particles are assembled inside the bacterium.
4. Lysis (Step 4): The bacterial cell bursts open (lyses), releasing the new bacteriophages (c) to infect other cells.

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Step 3: Describe the Lysogenic Cycle (Right Side)

The lysogenic cycle involves the integration of viral DNA into the host genome without immediate destruction.

5. Integration (Step 5): After penetration, the viral DNA integrates into the bacterial chromosome, becoming a prophage (d). This integrated DNA is replicated along with the bacterial DNA during cell division.
6. Replication (Step 6): The bacterium divides, and the prophage is passed on to daughter cells. The cell appears normal and healthy.
7. Induction (Step 7): Under certain conditions (e.g., stress), the prophage can excise itself from the bacterial chromosome and enter the lytic cycle.
8. Excision (Step 8): The prophage DNA is removed from the bacterial chromosome, initiating the lytic cycle.

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Final Answer:

Here are the labels for the diagram:

- a. Capsid (or Head) – contains the viral DNA.
- b. Tail fibers – used for attachment to the bacterial cell.
- c. New bacteriophages – produced during the lytic cycle.
- d. Prophage – viral DNA integrated into the bacterial chromosome.
- e. Bacterial chromosome with prophage – the host DNA containing the integrated viral genome.

Steps:

- 1. Attachment – Phage binds to the bacterium.
- 2. Penetration – Viral DNA is injected into the bacterium.
- 3. Biosynthesis – Viral components are synthesized and assembled.
- 4. Lysis – Bacterial cell bursts, releasing new phages.
- 5. Integration – Viral DNA becomes a prophage.
- 6. Replication – Bacterium divides, passing on the prophage.
- 7. Induction – Prophage excises and enters the lytic cycle.
- 8. Excision – Prophage DNA is removed from the bacterial chromosome.

This completes the solution to the problem.