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Questions and Answers
What is the primary purpose of the broth dilution assay?
What is the main difference between the plaque-forming assay and the broth dilution assay?
What is the primary mechanism by which a bacterial host becomes resistant to a phage?
What is the term for the process by which a phage infects a bacterial host and then remains dormant?
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What is the primary purpose of phage typing?
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What is the term for the study of the multiplication of a single phage over a single round?
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What is the primary advantage of the broth dilution assay over the plaque-forming assay?
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What is the term for the measure of the number of phages produced by a single infected bacterial host?
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What is the primary purpose of studying the life cycle of phages?
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What is the term for the process by which a phage infects a bacterial host and causes lysis?
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Study Notes
Lytic Cycle
- A virulent phage injects its DNA or RNA into the host cell
- Phage gene information is expressed, taking over the host cell's machinery to replicate the phage
- Upon completion of replication, the bacterial cell lyses, releasing new phage particles
- A plaque (zone of clearing) is formed when this process occurs on a lawn of agar-cultured bacteria
Lysogenic Cycle
- Some bacteriophages (temperate phages) have an alternate life cycle involving integration of the phage chromosome into the bacterial chromosome
- This is called the lysogenic cycle; integration is called lysogeny
- Lysogeny can persist for many bacterial cell cycles, but eventually comes to an end, and the lytic cycle is triggered
- Temperate phages (e.g., P1 and λ) may undergo the lytic cycle or integrate and maintain their chromosome in a stable, silent state within the bacteria (lysogenic state)
- The incorporated phage is known as a prophage, and lysogens are resistant to subsequent infections due to immunity provided by the prophage
Steps of the Lytic Cycle
- Attachment of the phage particle to the host cell
- Injection of the phage DNA into the host, followed by circularization of the phage chromosome
- Replication of phage DNA using host proteins and enzymes
- Transcription and translation of phage genes, and subsequent production of heads, sheaths, and tail fibers for assembly of progeny phage
- Packaging of phage chromosomes into phage heads
- Lysis of the host cell, and release of progeny phage particles
Phage Typing
- Identification of bacteria by testing their vulnerability to various bacteriophages
- A bacterial host may be infected by a range of phages
- A phage identifies and specifically binds to a host by binding to specific bacterial surface receptors
- Host cell may become resistant by surface mutations, or lysogenic conversion, which changes surface receptors and protects the host
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Description
This quiz covers the life cycle of virulent phages, including the injection of DNA or RNA into the host cell, gene expression, and replication. It also touches on the process of taking over the host cell's machinery and ultimately leading to the lysis of the bacterial cell.
