Since the discovery of restriction enzymes, the world of genetic engineering has become a major player in biotechnology. Genetically altering DNA sequences in prokaryotic and eukaryotic cells has provided hope to a plethora of issues which face mankind today. One of these issues is the buildup of greenhouse gases and the steady increase in global temperature since the industrial revolution of the early 1900s. Restriction enzymes have allowed scientists to isolate favorable traits that are represented in the DNA in plants, which could ultimately lead to these traits to be present in all plants. The way in which restriction enzymes work is invasive enough to successfully cut the desired DNA sequence. However it does not interfere with the replication or translation of the DNA and because of this characteristic it has become a staple of biotechnology research and product development. Although restriction enzymes work on the nano-scale level, the ramifications of harnessing the power of this naturally produced enzyme can provide possible solutions to issues which are on the macro-scale.
The facts, which support the notion that the world is slowly increasing in temperature, are irrefutable. According to research complied by the United State Environmental Protection Agency, the global mean temperature has risen between 1.0 and 1.7o F since 1850 (6). The temperature increase has a direct relationship with the increase of greenhouse gasses. Scientists have recorded a 36% increase in the amount of carbon dioxide in the atmosphere, whereas methane has seen a 148% increase since pre-industrial times (6). The increase in these two gasses is almost nearly all due to human involvement. The increase in the amount of greenhouse gasses in the future will also exponentially speed up the warming of the Earth. Projections estimate that the Earth will increase its surface temperature between 2 and 11.5oF by the end of the 21st century (6). Increases like these would severely cripple the size of the polar ice caps, and, subsequently, ocean levels would rise and then jeopardize the integrity of many major cities around the world.
However, this future scenario is not for certain. Many projections exist for the increase in greenhouse gasses and temperature, but these projections range significantly. These variations between the predictions are due to the unknown impact which humans may have on the environment. On one hand, CO2 and CH4 emissions may continue to increase exponentially, and when this is paired with no human effort to slow the temperature increase, the more extreme highs are produced. On the other hand, human involvement is the key to slowing down the global climate change. The human factors which would affect global warming include the following: stricter regulations on greenhouse gas emission, reducing consumption of fossil fuels, and using any form of technological advances to decrease the amount of greenhouse gasses in the air. These restrictions and technological advances are occurring all of the time, and one recent breakthrough is the use of restriction enzymes to genetically alter plants.
Restriction enzymes are like a pair of very accurate scissors on the cellular level. The enzymes are used to cut strands of DNA in a very particular location. These enzymes are not man made though; they were originally used as a defense mechanism against invading viruses. Bacteria needed a defense against bacteriophages and viruses, so restriction enzymes were developed to chop invading DNA in pieces which could be destroyed in the cytoplasm. “The endonucleases are termed ‘restriction enzymes’ because they restrict the infection of bacteriophages (2).” The enzymes take the invader’s genetic information and cut it into pieces which cannot interact with the bacteria’s own genetic information. This is an effective way of protecting the bacteria from bacteriophages or from other sorts of invading bacteria, but the enzyme needs to differentiate between its own genetic material and that of and invading bacteria.
Restriction sites come into the genetic scene now. Recognition of the proper location to cut enzymes uses two different elements which are described by Karl Drlica, a PhD in Molecular Biology:
“This recognition process involves two elements. First there are specific nucleotide sequences [As and Ts, Cs and Gs] that act as targets for the nuclease. These are called the restriction sites. Second, there is a protective chemical signal that can be placed by the cell on all the target sequences that happen to occur in its own DNA. The signal modifies the DNA and prevents the nuclease from cutting. Invading DNA's, lacking the protective signal, would be chopped by the nuclease (1).”
The specific site where the enzyme can make its cut is the restriction site. The second form of defense against destroying a bacteria’s own DNA is the presence of a chemical signal. The chemical signal is in the form of a methyl base. This base is paired with either an adenine or cytosine base on the DNA. However, the methyl base pairing will not affect DNA replication or the reading of the genetic code (2). This signal is placed on the sequence of nucleotides which happen to occur naturally in the bacteria’s own genetic code; thus, the enzyme cannot make its cut on the DNA. These elements of defense against the restriction enzymes are needed because restriction enzymes are so effective and precise in cutting DNA. This is exactly why the discovery of restriction enzymes was an integral part of furthering the scientific advances in the bionanotechnology field.
Restriction enzymes do two things, read and cut. Restriction enzymes are like a special form of DNAase, but the main difference is that restriction enzymes cut the DNA in a desired location, not just randomly. The enzyme reads the sequence of the DNA backbones, searching for a specific series which it would then bind itself to. The recognition sequence is normally four to six nucleotides long, and they are complementary to each other. This allows the same enzyme to cut both strands of DNA (3). The enzyme then separates the DNA in a specific way, either leaving a blunt end, or sticky end. A blunt end of cut DNA is a straight cut, which means that the DNA was cut in the exact same location on both the 5’ and the 3’ sides.
5'-CpTpGpApTpCpTpGpApCpTp GpApTpGpCpGpTpApTpGpCpTpApGpT-3'
3'-GpApCpTpApGpApCpTpGpAp CpTpApCpGpCpApTpApCpGpApTpCpA-5'
Figure 1. A blunt end cut on the DNA (5)
Sticky ends are created when the restriction enzyme cuts the 5’ and the 3’ sides at different locations on the DNA. The incisions are staggered so the opposing sides of the DNA have overhangs. The sticky end cuts are the most common type of cut on anti-parallel strands of DNA (3).
5'-ApTpCpTpGpApCpT pGpApTpGpCpGpTpApTpGpCpT-3'
3'-TpApGpApCpTpGpApCpTpApCpGp CpApTpApCpGpA-5'
Figure 2. A sticky end cut (5)
The reason that the restriction enzymes play such a major role in genetic engineering is because of the possibilities sharing DNA. The pieces of DNA which were cut by using restriction enzymes can then be bonded with any from of DNA which was cut with the same restriction enzyme. This way DNA from different sources can be bonded together, after they have been cut by using the same restriction enzyme.
Figure 3. EcoR1 restriction enzyme (4)
Figure 2 shows how the restriction enzyme EcoR1 can cut the DNA from two different sources. The restriction enzyme is characterized by the Pacman figure. Since the two different sources of DNA had been cut by using the same restriction enzyme, these strands of DNA can then be bonded together. The newly formed genetic material is called recombinant DNA. From here the recombinant DNA can have its genetic code translated into proteins. In essence, recombinant DNA is the heart of genetic engineering, and this is only made possible by the use of restriction enzymes.
Restriction enzymes are like the oil in a car. The engine cannot run without it, and in this case the engine is genetic engineering. Scientists have been able to harness the power of this molecular machine just like a bacteria cell uses it to fend off invading virus and other malicious strands of DNA. Restriction enzymes only have two tasks to perform, and they have become so efficient in completing these tasks with a high level of accuracy, that the future could be altered by the power which they could possibly create. A possible solution to global warming could be in the form of something which can’t even be seen by the naked eye. Restriction enzymes are a molecular machine which when combined with other scientific advances, like recombinant DNA, can create endless possibilities on the micro-scale level.
Works Cited
1. “Chapter 3: Genetic Engineering.” Science Clarified. 20 February 2008
2. Goodsell, David S. “Restriction Enzymes.” RCSB Protein Data Bank. 20 February 2008.
3. “Restriction Endonucleases.” The McGraw-Hill Companies, Inc. 20 February 2008
4. “Restriction Enzyme - Action of EcoRI.” Access Excellence at the
5. “Restriction enzyme.” Bio-Medicine.Org. 20 February 2008
6. United States Environmental Protection Agency. “Recent Climate Change. . .” 8 February 2008
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