an explanatin by the Slayer March 31, 2011 at 11:44am Define what a virus is. This is a page from my lecture notes: it clearly stats that biotech wants to use bacteria as a way to alter human DNA: Define what a plasmid is. Place viruses and other parasites into an evolutionary context. Demonstrate that understanding how viruses work led to recombinant DNA technology. In the last two lectures, we examined the types of controls that both prokaryotes and eukaryotes use to regulate expression of their genes. We noted that there is a huge difference between the relatively simple controls found in bacterial cells and in the multilayered, complex approach to gene regulation evolved by eukaryotic cells both in single-celled organisms and in multicellular organisms. Review this simple diagram below to recall that the anatomical complexity of the eukaryotic cell works to closely limit and control the types and amounts of proteins that are made during the lifetime of the cell. We also noted that this disparity between types and levels of control of gene expression in these two types of cells presents a challenge for biotechnology. Biotechnology seeks to utilize the simple protein synthesis machinery of the bacterium for the manufacture of eukaryotic proteins useful for humans. There must therefore be a way to bridge the gap between the simple mechanics of the prokaryotic cell and the complicated controls of the more complex eukaryote. Fortunately, there is such a bridge. Finding it involved investigation not only of prokaryotic and eukaryotic cellular mechanisms, but also of even simpler—but stranger—mechanisms used by the parasites called viruses. Viruses are considered nonliving entities, because they are not cells. They have a simpler anatomy than even the most basic prokaryote, and are missing key structures such as the plasma membrane, and the ribosomes that manufacture proteins. They even lack enzyme systems for making their own chemical energy! Viruses basically consist of an envelope, which can be made of protein, or a mixture of proteins and sugars; and a strand of nucleic acid, which serves as a library of genetic information for the viral type. Viruses may use RNA or DNA as their genetic material. Because viruses lack the machinery to capture their own chemical energy and to synthesize proteins, they cannot replicate themselves. This is another reason they are considered nonliving entities—because all living cells have the basic, necessary ability to make copies of their genetic material and of themselves. Viruses must therefore invade functional cells, either prokaryotes or eukaryotes, and trick those cells into using their own energy stores, raw materials, and manufacturing equipment to make more copies of the virus. After the cell has obliged its invader by making new viral particles, the cell may be forced to burst (or undergo lysis) to liberate the viruses. Viral infection thus often causes cell death and destruction of nearby tissues in a multicellular organism. An even more insidious method of viral replication, used by a number of dangerous viruses that cause human disease, involves further tricking the invaded cell to permit new viral particles to bud off from the surface of the cell. The virus can therefore keep its captive manufacturing plant alive long enough to make many more copies of itself before the cell dies. Viruses seem to be useless entities that perhaps can offer us nothing more than disease, tissue destruction, and even death. But they are also fascinating and instructive models for the process of subverting one cellular system to follow the instructions of quite a different cellular system. Therefore, viruses can teach us much about biotechnology. One of the first things scientists learned from viruses is that the direction of information flow in the cell as specified in the Central Dogma (that is, from DNA to RNA to protein) can be altered. Some viruses (they are viruses that use RNA as their genetic material) can teach the cells they invade to copy DNA from their RNA genome, and then use this complementary DNA (or cDNA) to direct the synthesis of proteins for the new viral particles. These types of viruses use a unique enzyme called reverse transcriptase to pull off this bit of genetic chicanery. Researchers wondered whether reverse transcriptase could be isolated and used to copy messenger RNA molecules into DNA. This would be a very useful method for specifically investigating (or probing) eukaryotic genes. Why? Because, as you recall, eukaryotic genes actually occur in segments rather than in unbroken sequences of DNA. Post-transcriptional processing of messenger RNA molecules splices together the information from these useful sequences. But if DNA can be reverse-transcribed from processed messenger RNA, eukaryotic genes can possibly be translated into proteins using the simpler systems of prokaryotic cells. Thats exactly what happened. Viruses not only gave us a reason to reconsider the universality of the Central Dogma, but also one very important clue as to how to bridge the gap between prokaryotic cell systems and eukaryotic cell systems. Understanding the tricks viruses play on their host cells thus led to the first real breakthrough in modern biotechnology. Thank you- Slayer
Posted on: Wed, 12 Mar 2014 06:56:57 +0000