why do viruses that infect bacteria have tails
1. Bacteriophages that replicate through the lytic life cycle are called lytic bacteriophages,
2. Adsorption is the attachment sites on the phage adsorb to receptor sites on the host bacterium. 3. Specific strains of bacteriophages can only adsorb to specific strain of host bacteria (viral specificity). 4. In the case of bacteriophages that adsorb to the bacterial cell wall, a bacteriophage enzyme drills a hole in the bacterial wall and the bacteriophage injects its genome into the bacterial cytoplasm. 5. The bacteriophage replicates its genome and uses the bacterium's metabolic machinery to synthesize bacteriophage enzymes and bacteriophage structural components. 6. During maturation, the bacteriophage parts assemble around the phage genomes. 7. A phage-coded lysozyme breaks down the bacterial peptidoglycan causing osmotic lysis and release of the intact bacteriophages. Even bacteriophages have similar shapes. They have a head that has a slightly spherical shape called an icosahedron. A tube connects the long legs to the head.
This shape affects the even bacteriophage functions. to summarize. , 821 829 (2009); published online 8 April 2009 [ [ Viruses are minuscule infectious particles composed of a protein coat and a nucleic acid core. They exist in a huge variety of forms and infect practically all living creatures: animals, plants, insects and bacteria. Insight into the infection process could facilitate new therapeutic strategies for viral and bacterial diseases as well as food preservation. An article by et al (2009) published in this issue sheds light on the still mysterious infection process. It reports the first crystal structure of a significant portion of the bacteriophages T4 tail sheath protein. Together with fittings into existing cryo-EM reconstructions, it suggests a mechanism of genome delivery into the host cell for the Myoviridae phages. Viruses can be considered as mobile genetic particles, containing instructions for reproducing themselves using foreign cellular resources. The amount of viruses that exist in the biosphere is enormous, varying in their virion shapes, genomes and lifestyles.
Classification of viruses is defined by host preference, viral morphology, genome type and auxiliary structures such as tails or envelopes. Viral particles outside a host cell (so called virions) are inert entities with a genome surrounded by a protective coat. Viruses that attack bacteria were named bacteriophages'. The term phage originates from Greek phagein, which translates as to eat'. The phage infection cycle seems to be simple but extremely efficient: a single phage injects its genome into a bacterial cell, switching the cells' programme in its favour so the host cell will eventually die and release about 100 new phage particles. Studies of bacteriophages became an essential part of biology because their omnipresence was tightly linked to bacteria. Analyses of bacteriophage genome sequences provide the opportunity to identify basic principles of genome organisation, co-evolution, as well as model and modify their genome.
Novel studies on the phage life cycle will not only reveal its interaction with biological barriers during viral transmission and high-level adaptation but might also help to overcome serious clinical problems caused by the occurrence of multi-resistant bacteria, the so-called superbugs'. This presumption is based on the fact that phages infecting certain bacteria may recognise and infect these despite their antibiotic(s) resistance. Indeed, exponential effects of phage growth in cells has proven very important in combating bacterial diseases. The Caudovirales order of bacteriophages is characterised by double-stranded DNA (dsDNA) genomes, which can be of the size from 18 to 500 kb in length. The phages, belonging to Caudovirales, account for 95 of all the phages reported in the scientific literature, and most likely represent the majority of phages on the planet ( ). Although genome sequences vary quite significantly, the virus particles of this group have a quite similar organisation: each virion has a polyhedral, predominantly icosahedral, head (capsid) that contains a genome.
The head is bound to a tail through a connector, and the distant end of the tail is equipped with a special system for piercing a bacterial membrane. The bacteriophage tail and its related structures are essential tools of the phage during infectivity process securing the entry of the viral nucleic acid into the host cell. Rossmann's group has been involved for many years with analysing different viruses and a significant part of their research is dedicated to the bacterial virus T4 that belongs to the Myoviridae family ( ). Myoviridae are a family of bacteriophages with contractile tails, comprising 25 of all known phage populations. Tail contraction is an essential phase of cellular infection by these phages, resulting in pressing the central tail tube through the outer cell membrane similar to a syringe, thereby creating a channel for DNA ejection from the capsid and into the host cell ( ; et al, 2003 ).
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