- Medicinal Chemistry
- Donlene Webb
- SMU
Viruses - A virus is a submicroscopic obligate parasitic particle that infects cells in biological organisms.
- Viruses are non-living particles that can only replicate when an organism reproduces the virulent RNA or DNA.
- Among other things, viruses do not move, metabolize, or decay on their own. Viruses are obligate intracellular parasites that lack the cellular machinery for self-reproduction.
- Viruses infect eukaryotes and prokaryotes such as bacteria; bacteriophages.
- Typically viruses carry a small amount of genetic material, either in the form of RNA or DNA, but not both, surrounded by some form of protective coat consisting of proteins, lipids, glycoproteins or a combination.
- The viral genome codes for the proteins that constitute this protective coat, as well as for those proteins required for viral reproduction that are not provided by the host cell.
Viruses - Viral nucleic acid can be DNA or RNA. It can be single or double stranded, circular or linear, with most being linear.
- The nucleic acid is protected from physical, chemical and enzymatic damage by a protein coat called a Capsid.
- Many viruses have a second envelope surrounding the Capsid on which there are spikes with antigenic determinants.
- This outer surface of the virus is responsible for host cell recognition. Initially viral proteins on the outer surface will attach to the hosts receptor molecules. A simplified viron is illustrated below.
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Life Cycle - ▪ Attachment, sometimes called absorption: The virus attaches to receptors on the host cell wall.
- Injection: The nucleic acid of the virus moves through the plasma membrane and into the cytoplasm of the host cell. The capsid of a phage, a bacterial virus, remains on the outside. In contrast, many viruses that infect animal cells enter the host cell intact.
- Transcription: Within minutes of phage entry into a host cell, a portion is transcribed into mRNA, which is then translated into proteins specific for the infecting phage.
- Replication: The viral genome contains all the information necessary to produce new viruses. Once inside the host cell, the virus induces the host cell to synthesize the necessary components for its replication.
- Assembly: The newly synthesized viral components are assembled into new viruses.
- Release: Assembled viruses are released from the cell and can now infect other cells, and the process begins again.
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