Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Medicinal chemistry A virus is an infectious agent found in virtually all life forms. Viruses consist of genetic material, and have a central core either DNA nor RNA Although they are infectious agents, they differ from bacteria in that they contain no nucleus or cytoplasm. They do not feed, excrete, or grow They cannot reproduce outside of a living cell. 2 There are many types of virus with varying shape and structure. All virus have a central core of either DNA or RNA surrounded by a coat of regularly packed protein units called capsid. No nucleus or cytoplasm like bacteria. Diagram of an AIDS Virus 3 The replication of viruses can only occur if the virus has attached and penetrated the living host cell. It injects it’s DNA or RNA into the host cell’s cytoplasm. It takes over the replication mechanism of the host cell. This causes the cell to die or to be altered, which results in the symptoms of a viral infection. The host cell produces new viral DNA or RNA cells which are then released to affect other healthy cells. A virus that contains RNA rather than DNA is called a retrovirus. 4 The virus uses the cell mechanism to replicate itself 5 Viruses cause a number of illnesses and diseases ranging from mild infections, such as the common cold, to potentially fatal diseases, such as acquired immunodeficiency syndrome (AIDS). It can be difficult to find effective methods of preventing and treating viral infections for a number of reasons: 1. Once inside a host cell, a virus can multiply very quickly and can have already spread throughout the body by the time that symptoms have appeared. 2. Viruses can mutate their DNA or RNA resulting in a slight change in viral structure – this can make them resistant to drugs and can prevent vaccinations from being effective; this is particularly true of viruses such as HIV. 3. Viruses use the host cell’s own processes and materials to produce new viruses, so it can be difficult to design drugs that target only the virus and do not affect the host cell. Several vaccines and antiviral drugs have been developed and used to prevent and treat viral infections successfully. Vaccines stimulate the body’s natural defences (the immune system) to produce antibodies against a virus – so if infection does occur, the immune system is prepared and can stop the infection before it takes hold. Vaccines have been used successfully against a number of viruses including measles, mumps and polio. Alter the genetic material Some alter the genetic material within cells – once inside a cell, the drug is converted into an active metabolite that becomes incorporated into the growing DNA strand (needed for viral replication) halting its synthesis. An example of a drug that acts in this way is aciclovir(acyclovir), which is used to treat cold sores; it stops viral DNA replication and so stops the virus from multiplying. Inhibit the activity of enzymes Some inhibit the activity of enzymes within the host cell that are necessary for the formation of new viruses. An example is indinavir, which is used in AIDS treatment; it inhibits the HIV enzyme protease, which is essential to the assembly of functional new HIV viruses. Preventing virus from binding host cells Some stop the viruses from infecting host cells by preventing them from binding to the host cell surface and gaining access into the cell. Some drugs used to treat AIDS work in this way Preventing virus from leaving host cell Some prevent the virus from leaving the host cell so that it cannot infect other cells – oseltamivir and zanamivir . Symptoms include fever, headache, aching joints and fatigue. In severe cases can even cause death There are many cases of pandemics such as “Spanish flue” in 1918 and swine flue in 2009. The influenza virus has RNA as its genetic material rather than DNA. The capsid contains RNA and RNA polymerase (an enzyme) and surrounding this it has a lipid envelope which has two very important proteins in it – neuraminidase (NA) and hemagglutinin (HA). Both proteins stick out of the membrane surrounding the virus. Hemagglutinin allows viruses to bind to receptors on the surface of cells to be infected Neuraminidase help virus to infect cell by breaking down its cell wall The virus enters the cell, replicates its RNA and essential proteins, but then the new viruses have to get out of the cell if they are to infect other cells. They do this by budding The virus will, however, remain bound to the surface of the until the NA breaks the link between the sialic acid and the rest of the membrane glycoprotein, allowing the virus to break free from the cell. Oseltamivir/zanamivir may be taken when fl u symptoms develop but they are also taken as a prophylactic (a preventative measure) for people who have been exposed to the virus or are in high-risk groups (such as very young children). Oseltamivir is administered orally as oseltamivir phosphate but zanamivir has very poor bioavailability when given orally and so is formulated as a dry powder for oral inhalation. Zanamivir is highly polar (see below) and cannot pass across cell membranes. A 10-year study completed in 2005 found a strain of Simian Immunodeficiency Virus (SIV) in a number of chimpanzee colonies in south-eastern Cameroon that was a viral ancestor of the HIV-1 that causes AIDS in humans. In 1981 AIDS was first identified within homosexual men 20 940,000 cases of AIDS were reported in the United States from 1981 through 2004. In 2004, about 39,000 new cases of HIV infection were reported. Currently, there are approximately 1.1 million people in the United States who are infected with the human immunodeficiency virus. 21 Wide spread in Africa. Lack of access to education. Reticence of some leaders to recognize the problem. Lack of access to treatment. 22 AIDS ( Acquired Immune Deficiency Syndrome) is caused by a retrovirus that contains RNA rather then DNA. This specific virus invades particular cells, that are within the immune system making the body unable to fight off infections. 23 The human immunodeficiency virus (HIV), which causes acquired immunodeficiency syndrome (AIDS), principally attacks T-4 lymphocytes, a vital part of the human immune system. As a result, the ability of the body to resist opportunistic viral, bacterial, fungal, protozoal, and other infections is greatly weakened. 24 Scientists have identified three ways that HIV infections spread: 1. Sexual intercourse with an infected person, 2. Contact with contaminated blood, 3. Transmission from an infected mother to her child before or during birth or through breastfeeding. 25 While no medical treatment cures AIDS, there are many drugs that have recently been developed to eradicate the HIV virus. Full blown symptoms of AIDS may not appear for more then 10 years. It usually takes 2-3 months after the initial infection for a person to test positive for HIV 26 While no medical treatment cures AIDS, there are many drugs that have recently been developed to eradicate the HIV virus. Although full blown symptoms of AIDS may not appear for more then 10 years. It usually takes 2-3 months after the initial infection for a person to test positive for HIV During this time frame a person inflected with HIV can easily spread the virus without realizing it. 27