Viruses: Complex Molecules Or Simple Life Forms? :: essays research papers

Viruses: Complex Molecules or Simple Life Forms? Viruses have been defined as "entities whose genomes are elements of nucleic acid that replicate inside living cells using the cellular synthetic machinery, and cause the synthesis of specialised elements that can transfer the genome to other cells." They are stationaryand are unable to grow. Because of all these factors, it is debatable whether viruses are the most complex of molecules or the simplest life forms. While the definition of living organisms must be adapted, the majority of evidence leads to the classification of viruses as living organisms. Viruses are composed of a nucleic acid core, a protein capsid, and occasionally a membraneous envelope. The nucleic acid core is composed of either DNA or in the case of retroviruses, RNA, but never both. In retroviruses, the RNA gets transcribed to DNA bye the enzyme reverse transcriptase. The protein capsid is a protein layer that wraps around the virus. There are four basic shapes of viruses. The tobacco mosiac, adenovirus, influenza virus, and t-even bacteriophage are each examples of a different virus structure. Each individual protein subunit composing the capsid is a capsomere. The tobacco mosiac virus has a helical capsoid and is rod shaped. The adenovirus is polyhedral and has a protein spike at each vertex. The influenza virus is made of a flexible, helecal capsid. It has an outer membranous enevelope that is covered with glycoprotein spikes. The T-even bacteriophage consists of a polyhedral head and a tail. The tail is used to inject DNA into a bacterium while the head stores the DNA. Basic life is defined as the simplest form capable of displaying the most essential attributes of a living thing. This makes the only real criterion for life the ability to replicate. Only systems containing nucleic acids are capable of this phenomenon. With this reasoning, a better definition is the unit element of a continuous lineage with an individual evolutionary history. Because of viruses inability to survive when not in a host, they must have evolved from other forms of life. The origin of viruses is an easy thing to theorize about so many hypothesese have been made. One such hypothesis is that viruses were once complete living parasites. Over time they have lost all other cellular components. This is backed up by the idea that all cells degenerate over time. Some people think along very similar lines that viruses are representatives of an early "nearly living" stage of life. This goes along with the first hypothesis in that it accounts for a loss of components. All creatures that become parasitic can be seen losing their obsolete functions and