Bacteriophages: Structure, Composition, and Analysis

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Questions and Answers

What is a drawback of traditional antibiotics in combating pathogenic microorganisms?

Resistance to antibiotics is not limited to targeted bacteria, and it can take several years to develop new antibiotics.

What mechanism do bacteria use to protect their own DNA from restriction endonucleases?

Modifications such as methylation.

What is the primary application of CRISPR technology?

Gene editing.

How do phages play a role in the development of CRISPR technology?

Phages leave behind short DNA sequences in the genome of bacteria, which are used in CRISPR technology. Signup and view all the answers

What is a key difference between traditional antibiotics and phage therapy?

Phage therapy has few minor side effects, whereas traditional antibiotics have multiple side effects, including secondary infections. Signup and view all the answers

What is the primary function of the plaque assay in bacteriophage analysis?

To detect and isolate bacteriophages from an environmental sample Signup and view all the answers

How do temperate phages differ from lytic phages in terms of their replication cycles?

Temperate phages can undergo both lytic and lysogenic cycles, while lytic phages can only undergo lytic cycles Signup and view all the answers

what forms the prophage and in what cycle?

prophage forms when a viral genome integrates into the host genome. in lysogenic cycle Signup and view all the answers

What determines whether a bacteriophage will undergo a lytic or lysogenic cycle?

The transcription factors C1 and Cro in the phage genome, which regulate the synthesis of genes involved in the lytic or lysogenic cycles Signup and view all the answers

What is the structural characteristic of icosahedral bacteriophages?

They have a polyhedral shape with 20 triangular faces Signup and view all the answers

During the lytic cycle, what is the function of the enzymes that break the cell's peptidoglycan, leading to osmotic lysis?

They release the newly assembled phage particles from the host cell, allowing them to infect other cells Signup and view all the answers

How do the C1 and cro proteins compete with each other in the operator region of the phage genome?

C1 and cro proteins physically compete with each other in the operator region, with more C1 binding leading to lysogenic cycle and more cro binding leading to lytic cycle. Signup and view all the answers

What is the role of CII protein in phage development, and how is it regulated?

CII protein monitors the health of the host cell and decides which cycle to choose; it is sensitive to degradation by host proteases, such as HfLA. Signup and view all the answers

How does the phage switch between lysogenic and lytic cycles in response to host cell conditions?

When the host cell is growing and has enough nutrients, CII is degraded, leading to lytic growth; when nutrients are scarce, CII is activated, leading to lysogenic growth. Signup and view all the answers

What is the significance of lysogenic conversion, and how does it contribute to antibiotic resistance?

Lysogenic conversion can transform non-virulent bacteria into highly virulent pathogens, which can contribute to the development of antibiotic resistance. Signup and view all the answers

What are the four principles of phage therapy, and why are they important?

The four principles are: phage must be lytic, a single dose treats infection, phage is non-toxic and specific, and phage-mediated lysis is effective against antibiotic-resistant bacteria. Signup and view all the answers

How do bacteriophages differ from antibiotics in their mode of action, and what are the implications for their use in treating infections?

Bacteriophages target a narrow host range, whereas antibiotics have a broader spectrum; phages are effective against antibiotic-resistant bacteria. Signup and view all the answers

Study Notes

Bacteriophage Cycles

C1 facilitates the synthesis of genes needed for lysogenic cycle, while Cro facilitates the synthesis of genes needed for lytic cycle.
The region between C1 and Cro is operator sequences, which they interact with and physically compete for.
More C1 binding to the operator region means it will outcompete Cro and undergo lysogenic cycle, and vice versa.

Phage Switching Mechanism

CII is a protein involved in monitoring the health of the cell and decides which cycle to choose accordingly.
CII is sensitive to degradation by host proteases, specifically HfLA.
When cells are actively growing and have enough nutrients, they produce high levels of HfLA, degrading CII, leading to lytic growth.
When cells have limited nutrients, they produce less HfLA, allowing CII to activate and promote lysogenic growth.

Lysogenic Conversion and Phage Therapy

Lysogenic bacteriophages can contribute to the development of antibiotic resistance.
Phage therapy uses lytic bacteriophages to treat pathogenic infections, with four principles:
- Phage must be lytic.
- A single dose of phage should treat infection.
- Phage is non-toxic and highly specific for targeted bacterial populations.
- Antibiotic-resistant bacteria remain sensitive to phage-mediated lysis.

Bacteriophages Characteristics

Bacteriophages usually target a very narrow host range, requiring the disease-causing bacterium to be identified.
They have different shapes, genetic composition (single or double-stranded, RNA or DNA), and genome size (4 to 100s of genes).

Phage Analysis and Isolation

Plaque assay is used to analyze and isolate phages, involving:
- Sample collection from the environment.
- Sample dilution.
- Mixing with appropriate host cells.
- Pouring on agar plate.
- Incubation to allow growth.
- Plaque formation, creating a clear zone in the bacterial lawn.

Bacteriophage Structure and Types

Structure can be icosahedral or filamentous.
There are two types of bacteriophages:
- Lytic phages, which can only undergo lytic cycles.
- Temperate phages, which can undergo lytic and lysogenic cycles.

Lytic and Lysogenic Cycles

Lytic cycle:
- Adsorption/attachment.
- Penetration.
- Replication and synthesis.
- Assembly.
- Release.
Lysogenic cycle:
- Attachment/adsorption.
- Penetration.
- Prophage formation.
- Maintenance.
- Spontaneous induction.
- Replication and synthesis.
- Assembly.
- Release.

Phage Defense Mechanisms

Bacteria possess different ways to fight against viral attacks, including:
- Restriction endonucleases, which recognize short and specific sequences and cut them.
- CRISPR (clustered regularly interspaced short palindromic repeats), a system that protects hosts' own DNA by modifications such as methylation, and has applications in gene editing.

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Description

This quiz covers the genetic composition and structure of bacteriophages, including their genome, shape, and types. It also explores the analysis and isolation of phages using plaque assay. Test your knowledge of these microorganisms!