Bacteriophage: Definition, Structure, Diagram, and Function

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What is Bacteriophage?

Bacteriophage is nothing but an organism which eats a bacterium. As the name suggests that these are viruses which replicate and infect within the cells of the bacteria.

These are commonly called as phages and are found everywhere which is said to be omnipresent.

Bacteriophages contains both DNA and RNA as a nucleic acid in their genomes, which is found encapsulated in a protein coat which also infects other organisms like archaea.

The activity performed by bacteriophages to kill the bacteria is known as bactericidal property.

Which is first observed by Ernest Hanbury Hankins in the Ganges river water, which has the capability to kill cholera bacteria.

There are exists many types of viruses which kills certain bacterias respectively. These viruses act in the same way that how the antibodies affect the cell wall of the bacteria.

They also have the potential to act against antibody resistant pathogenic bacteria.

Features of Bacteriophage

A bacteriophage is made up of a protein coat which is known as capsid, it also encapsulates the genome and also consists a head like structure which is polyhedral in shape. Bacteriophages may be enveloped or non-enveloped.

They also have different shapes. The shapes of bacteriophages include rod-shaped, filamentous, isometric, etc.

The capsid of the bacteriophage is made up many numbers; of capsomeres. The size and shape of the capsomeres varies accordingly depending upon the number of species.

The genome is made up of DNA or RNA, they may be ss or ds DNA or RNA. It may also be linear or colinear.

The genomes which codes for the proteins ranges from four to hundred. Whereas the MS2 bacteriophage genome codes for the four proteins.

However, the largest genome which is present in a bacteriophage is of 735kbp. The tail of the bacteriophage may be long or short, and either be contractile or non-contractile.

The tail contains fibers which helps in anchoring the virus to the bacterial cell wall.

Classification of Bacteriophage

Bacteriophages are classified based on the content of nucleic acid present in there and also based on their morphological characteristics.

There are almost 19 families of bacteriophages, two of these two families belong to the RNA bacteriophages.

Even several types of bacteriophages exist in this environment, but only one type can infect that one specific type of bacteria.

Characteristic of Bacteriophage

They are generally classified into a number of virus families such as Inoviridae, Microviridin Rudiviridae and Tectiviridae.

Like many other viruses’ bacteriophages are also simple organisms which consists a core of genetic material which is surrounded by a protein capsid.

Bacterial DNA Transduction - Bacteriophage- Definition, Structure, Diagram, and Function - research tweet

The genetic material present in the bacteriophages may be either RNA or DNA. After infecting a cell, bacteriophages completely take control of the host cells and stops it from producing the components of bacteria and it also forces it to produces viral components which affects the normal activities of the cell.

This also eventually induces out the lysis of the host bacterial cell. They are involved in the process of transduction, where the bacteriophages occasionally remove the portion the DNA in the host cell and further transfers it into genome of the host cell.

Structure of Bacteriophage

Generally, a typical bacteriophage is comprising of a head, which is polyhedral in shape, a short collar and a helical shaped tail.

The head of the bacteria phage is polyhedral in shape and consists of about 2000 capsomeres long with the genetic material.

Bacterial DNA Transduction - Bacteriophage- Definition, Structure, Diagram, 1 and Function - research tweet

The genetic material is composed of either double stranded DNA or single stranded RNA with is present being enclosed within the head.

The tail of the bacteriophage looks like a hollow tube on its interior side and it is surrounded by a contractile sheath which has about 24 annual rings.

The distal end of the tail is composed of basal plate which has the tail fibers at each of its corner.

Life Cycle of Bacteriophage

When the bacteriophage enters the host cell it inserts its genetic material into the host cell and it undergoes two stages of life cycle namely Lytic cycle and Lysogenic cycle.

Lytic cycle is also known as Virulent cycle, whereas the Lysogenic cycle is known as Temperate cycle.

Lytic Cycle

While undergoing the lytic cycle, bacteriophages tend to infect the host cell and kills it, so that it releases the progeny viruses.

They are several steps involved in the process of lytic cycle as adsorption, penetration, synthesis of phage components, maturation and assembly and release.

Lytic and Lysogenic Cycle- Bacteriophage- Definition, Structure, Diagram, and Function - research tweet
I. Adsorption

This is the first step involved in the process of lytic cycle. Here the bacteriophage attaches itself to the surface of bacteria which is a host cell. It attaches the tip of the tail fibers which attaches specifically to the specific receptor sites on the surface of the host cell.

II. Synthesis of Phage Components

After the release of genetic material from bacteriophage into the host cell many components of new virus particles are released.

The sub units of the bacteriophage which includes the head, tail and late protein appears in the host cell. Whereas the early proteins and specific enzymes helps in carrying out the synthesis.

Components of GH phage are present in the nucleus and cytoplasm of the host cell.

III. Maturation and Assembly

When these cells mature, the head and tail protein of the phage DNA is surrounded by protein coat assemble. Apart from this to these virions are formed by addition of tail structures.

IV. Release

The lysis of the bacterial cell occurs by releasing the progeny during the process of replication, Phage enzymes weakens the cell of the bacteria.

Lysogenic Cycle

It is considered as the other pathway for reproduction of the virus in the host cell. During this phase, the integration of the phage nucleic acid into the host cell genome or either the formation of circular replicon in the host cells cytoplasm take place.

The host cell continuous to live and reproduces normally during this cycle. The genetic material of the phage is called prophage viruses which does not lyse so it is known as lysogenic bacteria.

During the multiplication of lysogenic bacteria, the prophage may lose due to excision.

Bacteriophage Citations


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