From the deadly AIDS causing HIV (human immunodeficiency virus), and the threatening H1N1 virus causing swine flu to the one causing common cold, viruses have been a bane for the human race for a long time. What is it that makes them the most ingenious non-living parasites, which can infect all types of organisms, bacteria, plants as well as animals?
Viruses have brilliant morphology which is most suited for the basic prerequisites of survival and multiplication. A virus is nothing but a small piece of genetic information, either DNA or RNA encapsulated, and protected by a capsule or coat made up of protein. In some cases there is an envelope of lipids surrounding the protein capsule. The viral nucleic material most often codes for the specific protein coat which protects it and in some instances for some proteins (enzymes) necessary in the process of its replication/ multiplication. Viruses exist in a variety of shapes ranging from helical to icosahedral to more complex structures. They are classified on the basis of numerous factors such as morphology (appearance), diseases caused, host organism of choice, type of nucleic acid and so on. Two main theories are proposed about the origin of viruses, namely, degeneracy and drifted genes. According to the first theory, viruses were small parasitic cells thriving on larger cells which due to loss of function (degeneracy) evolved into a separate independent existence. However, some scientists insist that some nucleic material from the genes of larger organisms managed to escape to exist separately or independently (known as drift/ vagrancy).
Most viruses entirely use the host’s DNA replication machinery to multiply in order to survive. Their brief or long term association with the host is actually a very elaborate virus multiplication cycle.
This cycle starts with the attachment of the virus body to the host cell, followed by its penetration into the cell. Once inside the cell, the virus capsule starts uncoating so as to release the encapsulated nucleic material within the cell. This nucleic material then interacts with DNA of the host and is replicated several times by the host’s replication machinery. The copies of viral DNA are then reassembled into protein capsules by a process termed ‘assembly’. Once the tiny viruses are ready, they escape out of the host by a process of ‘release’ which most of the time is fatal to the host. These new viruses then continue the cycle by attaching onto or infecting other host cells. Some viruses carry the gene coding for some of the enzymes required for their multiplication. The multiplication cycle slightly varies for each viral family/class albeit the basic process remains the same for all.
Something as common as a cold is also caused by these viruses. The common cold is a viral infection caused by the Rhinovirus, a type of Picornavirus. These viruses attack the host and establish their temporary habitat in the upper respiratory tract affecting the host’s nose, throat and sinuses in the process. The virus is transmitted into the host’s body in the form of aerosols or by direct contact with another infected entity. Cold and wet weather increases the chances of viral transmission. The symptoms of the common cold arise from the immune response of the body against the viral invasion. There is no cure for the common cold yet; however the medication we usually take is to treat the symptoms and not the virus. This information is just the tip of a huge iceberg that is Virology, encompassing the vast and detailed study of viruses.