BACTERIOPHAGES Flashcards
Bacteriophages are viruses that infect bacteria
The phages have very complicated structure and are called——-
They are ——–shaped
They consist of ———– from each angle of which —–. Due to these, phage is adsorbed on the bacteria cell.
The phages have very complicated structure and are called complex viruses.
They are tadpole or spermatozoid shaped.
They consist of head, neck, tail and basal plate from each angle of which six teeth and filaments going out. Due to these, phage is adsorbed on the bacteria cell
the hexagonal head is containe the—–
The head is surrounded with ——The neck is free of this membrane
The tail is composed of a —– surrounded with —- and formed the cylindrical symmetry and the free filament of nucleic acid is hanged in this cylinder
basal plate is containe the———
Due to this—— phage breaks down a portion of the bacterial cell wall and penetrates through the cell wall of bacteria.
The nucleic acid DNA or RNA is contained in the hexagonal head. The head is surrounded with
protein membrane or capsid. The neck is free of this membrane. The tail is composed of a hollow core
surrounded with protein membrane and formed the cylindrical symmetry and the free filament of nucleic
acid is hanged in this cylinder. The lysozyme enzyme is contained in the basal plate. Due to this lysozyme
phage breaks down a portion of the bacterial cell wall and penetrates through the cell wall of bacteria.
The interaction of phage and bacteria is manifested in the following phases occurring in succession:
Adsorption
Penetration into the cell
Reproduction: biosynthesis, maturation
Release
The interaction of phage and bacteria
1. Adsorption
After a chance collision between phage particles and bacteria, attachment, or adsorption, occurs.
During this process, the attachment site on the virus attaches to a complimentary receptor site on the bacterial cell.
This attachment is a chemical interaction in which weak bonds are formed between the attachment and receptor sites. The complementary receptor sites are on the bacterial cell wall.
The interaction of phage and bacteria
2. Penetration.
After the attachment the bacteriophage injects its nucleic acid into the bacterium.
To do this, bacteriophage’s tail releases an enzyme, phage lysozyme, which breaks down a portion of the
bacterial cell wall.
During the process of penetration the tail sheath of the phage contracts and the tail core is driven through the cell wall.
When the tip of the core reaches the plasma membrane, the DNA from the bacteriophage’s head passes through the tail core and through the plasma membrane and enters the bacterial cell
The interaction of phage and bacteria
3. Biosynthesis.
Is the process when the nucleic acid is integrated in the bacterial genetic material and the synthesis of substrates necessary for the phage takes place.
the phage uses the host cell’s nucleotides and several of its enzymes to synthesize many copies of phage DNA. Soon after, the biosynthesis of the viral proteins begins.
The interaction of phage and bacteria
4. Maturation and Release
In the next sequence of events, maturation occurs. In this process,
bacteriophage DNA and capsids are assembled into complete virions. The phage heads and tails are
separately assembled from protein subunits and the head is filled with phage DNA and attached to the
tail. After self-collection the phages are released from the bacterial cell and affect that cell. These viruses
are termed virulent phages. In contrast to virulent bacteriophage some viruses do not cause lysis and
death of host cell when they multiply. These ones called temperate phages penetrate into the bacterial
cell then integrate in the genetic material of the bacteria (bacterial chromosome). The integrated into nucleic acid phage is known as a prophage. The prophage behaves like a segment of the host chromosome
and replicates with it. This phenomenon is called lysogeny, and a bacterium that carries a prophage
within its genome is called lysogenic bacterium.
