Bacteriophages and Their Life Cycles

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Questions and Answers

What is a nucleic acid genome?

It passes information from one generation to the next and all viruses have one.

What is a capsid?

A protein coat that surrounds the nucleic acid core.

What is an envelope in relation to viruses?

It surrounds the capsid but only some viruses have this, not all.

What are bacteriophages?

Viruses that infect bacteria. Signup and view all the answers

What is phage typing?

Identification of bacterial strains using infectivity by different bacteriophages. Signup and view all the answers

A virulent phage reproduces only by a lytic cycle.

True Signup and view all the answers

What happens during the lytic cycle?

A virulent phage enters the bacterial cell, takes over the activities of the cell to produce copies, and the host cell bursts, releasing new viruses. Signup and view all the answers

A temperate phage can only replicate by a lytic cycle.

False Signup and view all the answers

What occurs during the lysogenic cycle?

A temperate phage enters a bacterial cell and integrates its nucleic acid into the host DNA, allowing the host to remain alive while replicating. Signup and view all the answers

What is a prophage?

The phage nucleic acid that becomes integrated into the host DNA and replicates with it. Signup and view all the answers

What is non-integrative lysogeny?

Certain temperate phages may enter the bacterial cell and stay in the cytoplasm as a plasmid, replicating independently. Signup and view all the answers

What are plaques?

Patches of lysis and areas of lysed bacteria representing one initial bacteriophage. Signup and view all the answers

What is the purpose of the bacteriophage specificity exercise?

To identify potential lysis within a bacterial lawn. Signup and view all the answers

How do you know if bacteriophage infected the bacteria?

By using the process called phage typing, where plaque formation indicates bacteriophage infection. Signup and view all the answers

Why didn't bacteriophage infect all three bacteria?

Because they have to be a match; if they do not match, the virus cannot enter the host cell and cannot infect it. Signup and view all the answers

What is the explanation for bacteriophage specificity when it comes to infecting specific bacteria?

Viruses only infect those cells that have a matching protein to the one found on the virus capsid. Signup and view all the answers

Describe how this exercise demonstrates the principle of phage typing.

It showed what bacteria were sensitive to lytic T4-phage suspension. Signup and view all the answers

List other biological examples in which specific protein interactions are involved.

Pull-down assay, yeast-two hybrid assay. Signup and view all the answers

Study Notes

Bacteriophage Basics

Nucleic Acid Genome: Essential for passing genetic information across generations; present in all viruses.
Capsid: A protective protein coat encasing the nucleic acid core of a virus.
Envelope: A lipid layer surrounding the capsid; found only in some viruses.

Bacteriophage Characteristics

Bacteriophages: Viruses specifically designed to infect bacteria.
Phage Typing: A method to identify bacterial strains based on their susceptibility to various bacteriophages.

Phage Life Cycles

Virulent Phage: Completes reproduction solely through the lytic cycle.
Lytic Cycle: Compromises the host cell immediately, replicating the phage and causing cell lysis within approximately 30 minutes, producing 100 to 200 new virions.
Temperate Phage: Capable of replicating through either the lytic cycle or the lysogenic cycle.

Lysogenic Cycle and Prophages

Lysogenic Cycle: The temperate phage integrates its nucleic acid into the host DNA, allowing it to replicate without harming the host; can switch to lytic cycle if triggered.
Prophage: Integrated phage nucleic acid that replicates along with host DNA.
Non-Integrative Lysogeny: Some temperate phages remain in the cytoplasm as plasmids without integrating into the host DNA, reproducing independently or with the host.

Plaques and Infection Indicators

Plaques: Zones of bacterial lysis on a culture, indicating phage activity; represent individual bacteriophage origins.

Bacteriophage Specificity

Phage Infection Criteria: Bacteriophages require a match between their capsid proteins and the host's cell surface to successfully infect.
Mismatch Causes: If there’s no protein match, the virus cannot penetrate and infect the bacterial cell.

Experiment Purpose and Biological Examples

Exercise Goal: Identify potential lysis through plaque formation on a bacterial lawn.
Phage Typing Principle: Demonstrated sensitivity of certain bacteria to the lytic cycle of specific phages, such as T4-phage.
Specific Protein Interactions: Related biological processes include pull-down assays and yeast-two hybrid assays, which also explore protein interactions.

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Description

Test your knowledge on bacteriophages, including their structure, characteristics, and life cycles. This quiz covers essential concepts like the lytic and lysogenic cycles, as well as the role of phage typing in identifying bacterial strains. Dive into the fascinating world of viruses that target bacteria!