In the plaque assay, what is the precise origin of 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 by forming clear zones called plaques on a layer of host cells.

Recognize that each plaque originates from a single infectious virus particle, often referred to as a plaque-forming unit (PFU).

Know that when a single virus particle infects a host cell, it replicates and causes cell lysis, releasing progeny viruses that infect neighboring cells, leading to a localized area of cell destruction visible as a plaque.

Therefore, the precise origin of a single plaque is one infectious virus particle that initiated infection in a single host cell.

This concept is fundamental because counting plaques allows estimation of the number of infectious virus particles in the original sample.

Key Concepts

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

Plaque Assay Technique

The plaque assay is a method used to quantify viruses by infecting a layer of host cells and observing clear zones called plaques. Each plaque represents an area where the virus has lysed the host cells, allowing researchers to estimate viral concentration.

Origin of a Single Plaque

A single plaque originates from one infectious viral particle, or virion, that infects a host cell and initiates a localized infection. This infection spreads to neighboring cells, causing cell lysis and forming a visible plaque.

Host Cell Lysis and Viral Replication

After a virus infects a host cell, it replicates inside until the cell bursts (lysis), releasing new virions. These progeny infect adjacent cells, leading to a chain reaction that creates the clear zone observed as a plaque.

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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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