In the plaque assay, exactly what makes up a single plaque?

Verified step by step guidance

Understand that a plaque assay is a method used to quantify the number of virus particles capable of infecting cells in a sample.

Recognize that a single plaque represents a clear zone on a layer of host cells where the virus has infected and lysed the cells.

Know that each plaque originates from a single infectious virus particle, also called a plaque-forming unit (PFU).

Realize that the virus infects a host cell, replicates, and spreads to neighboring cells, causing cell death and forming the visible plaque.

Therefore, a single plaque is made up of a localized area of lysed host cells resulting from infection by one infectious virus particle.

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Plaque Assay

A plaque assay is a laboratory method used to quantify the number of infectious virus particles in a sample by infecting a layer of host cells. Each infectious virus particle infects a cell and spreads to neighboring cells, creating a clear zone called a plaque where cells have been destroyed.

Plaque Formation

A single plaque forms when one infectious virus particle infects a host cell and replicates, causing cell lysis. The infection spreads locally to adjacent cells, resulting in a visible clear area or plaque, which represents the progeny of that original virus particle.

Relationship Between Plaques and Virus Particles

Each plaque corresponds to one infectious virus particle, also called a plaque-forming unit (PFU). Counting plaques allows estimation of the concentration of infectious viruses in the original sample, assuming each plaque arises from a single virus.

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Textbook Question

The bacteriophage genome consists of many genes encoding proteins that make up the head, collar, tail, and tail fibers. When these genes are transcribed following phage infection, how are these proteins synthesized, since the phage genome lacks genes essential to ribosome structure?

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Textbook Question

A plaque assay is performed beginning with 1 mL of a solution containing bacteriophages. This solution is serially diluted three times by combining 0.1 mL of each sequential dilution with 9.9 mL of liquid medium. Then 0.1 mL of the final dilution is plated in the plaque assay and yields 17 plaques. What is the initial density of bacteriophages in the original 1 mL?

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Textbook Question

Define plaque, lysogeny, and prophage.

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