This process culminates in the de novo synthesis of viral proteins and genome. Bacteriophages may have a lytic cycle or a lysogenic cycle, and a few viruses are capable of carrying out both. Medical Microbiology 4 th Edition. If a host cell does not provide the enzymes necessary for viral replication, viral genes supply the information to direct synthesis of the missing proteins. These viral proteins are all synthesized in the cytoplasm, then imported into the nucleus. Figure 10 Rhabdovirus assembly Nucleocapsid Synthesis of the nucleocapsid was described above. There are two main ways that viruses reproduce or multiply and these are listed below.
The genome, having +ve polarity, itself act as the messenger, specifying information for the synthesis of both structural and nonstructural proteins. The seven classes of viruses are listed here briefly and in generalities. Examples of this class include the families , , and. This is a very odd feature of the rotaviruses. There is no distinction between early and late functions.
These changes, called cytopathic causing cell damage effects, can change cell functions or even destroy the cell. These sequences may respond in trans to products produced by other genes and act in cis on the associated genes. Viruses can spread faster than thought possible by surfing from cell to healthy cell while skipping cells that are already infected, scientists have discovered. The naked virus capsid then dissolves, releasing its genetic code. Hoping someone can answer this one or provide a web link to another source? Adsorption and penetration The virus binds to cell surface receptors. However, none interfere with the particular mechanism described in the current study. The most intensively studied member is vesicular stomatitis virus.
The significance of this is unclear. On reaching the nucleus, the terminal ends undergo limited exonucleotic digestion and then pair to form circles. Figure 18A Herpes simplex virus in cellular vacuoles and cytoplasm of peripheral blood lymphocyte ©. This acid takes the host cell hostage and the virus begins to multiply with nucleic acid and its protein coat thus developing into new viruses. New full length minus strands may serve as templates for replication, or templates for transcription, or they may be packaged into new virions. They are replicated in the nucleus of infected cells by host enzymes through double stranded intermediates.
This specificity determines the host range tropism of a virus. However, nucleases in the body probably greatly limit its role. The attached virus is taken up by endocytosis. Each animal virus can replicate only in a certain range of cells. Virion release: There are two methods of viral release: lysis or budding. The virion is endocytosed and contained within a cytoplasmic vacuole.
This class includes two major families, the and. Replication is within the cytoplasm. This is translation of the genome into protein produces. Enveloped Viruses - Viral proteins are first associated with the nucleic acid to form the nucleocapsid, which is then surrounded by an envelope. In the clinical laboratory, this may enable virally-infected cells to be detected at an early stage in infection, and may allow detection of viruses which do not visibly damage the cell. Nucleocapsids are transported out of the nucleus while envelope proteins are transported via the Golgi body to the plasma membrane. It is this process that results in the acquisition of the viral phospholipid envelope.
Copyright 1999 Dr Tim Baker and Stepthen M Spencer. Uncoating A key step in uncoating is the acidification of the content of the endosome to a pH of about 5, owing to the activity of a proton pump present in the membrane. Naked icosahedral viruses are released from infected cells in different ways. The genetic sequence begins to replicate. This is the reason why many will refer to the process as reproduction. This fusion is equivalent to the fusion of the virion's envelope with the plasma membrane of the host cell at the onset of infection.
Capsomeres are arranged in a precise and highly repetitive pattern around the nucleic acid. They are small enough to be imported into the nucleus through the nuclear pore complex, and uncoating occurs in the nucleus. During maturation, unit-length molecules are cut from the concatemers. These types of viruses enter into the host cell's cytoplasm as before. They are small ~40nm diameter , icosahedral, non-enveloped viruses that replicate in the nucleus. Penetration Penetration rapidly follows adsorption, and the virus can no longer be recovered from the intact cell.
The new viruses may invade or attack other cells, or remain in the cell. Release This probably occurs via cell lysis. A copy of the worm scans the network for another machine that has a specific security hole. In all three cases, once all the genes are copied and proteins structures are assembled, the baby viruses can leave the cell and fizz away into the air, only to be inhaled by another unsuspecting host. International committees have recommended genus and family names for certain viruses, but the process is still in a developmental stage.