StemCell Therapy

The mutations we've been discussing occur in a seemingly random manner by various mutagens. Mutation can also be caused in a very systematic way by viruses. Viruses can enter a host cell and then alter the DNA of the host cell by clipping it open and inserting new segments that will code for the viral protein, and they can do that by using the host cell's replication, transcription and translation mechanisms to create that viral protein.

This scenario is also related to the field known popularly as genetic engineering. Basically, it involves altering the DNA in a simple organism such as a bacterium in order to get the bacteria to produce a protein that it ordinarily would not produce, and this is done by snipping open a section of the bacterial DNA and inserting a gene from another organism. The technique is called gene splicing and it is often accomplished by inserting the new gene in a virus and then infecting the bacteria with the virus.

Here is one mechanism by which this can occur. Certain enzymes can open up the DNA sequence by breaking or hydrolyzing the phosphor ester bond in the DNA backbone.

In the lesson on proteins, I mentioned a disorder called diabetes, in which the messenger protein, insulin, is defective. Early treatment for this disease involved injecting insulin into patients in order to enable their cells to take up glucose. One problem with this treatment was that the only insulin available at a reasonable cost was insulin from cows. This insulin was slightly different and therefore not as effective as human insulin; moreover, some diabetics had what amounted to an allergic reaction to the foreign protein. In timet, genetic engineers were able to insert the gene for human insulin into a common bacterium called E. coli. When this bacterium was then grown in cultures, it produced vast quantities of human insulin which could be isolated fairly easily in pure form, for use by diabetics. Moreover, the human insulin was much cheaper when produced in this way than was the insulin from cows.

Another protein produced in this way is the protein interferon. When it was originally discovered, it was thought to be a potent cure for cancer and highly effective at preventing viral infection, and perhaps it might even be the long sought cure for the common cold. Unfortunately, it was incredibly expensive to isolate and available only in minute quantities. Not only was it impractical to use on a wide scale, it was not possible to do meaningful research with it, because such small amounts were available. A great deal of effort was expended to genetically alter bacteria to produce interferon. Effort which was eventually successful. Unfortunately, when sufficient quantities of interferon were produced to adequately test its abilities as an anti-cancer drug, it was found to be not nearly as effective as had been hoped.

Although genetic engineering would seem to be a marvelous new technique and it surely is that, it also has certain dangers associated with it. One problem is that when the genetic makeup of an organism is altered, it is not possible to predict exactly what the nature of that organism might be. If there is something inherently harmful about the new organism and that organism is released to the environment, the results could be disastrous. This danger is usually dealt with by using, as the host organism, a bacterium which is, somehow deficient and cannot survive outside the laboratory.

Another problem is that a future step in genetic engineering might well involve the ability to alter the genetic makeup of higher organisms, including humans. There are difficult ethical questions involved in how far we should go in changing our own genes, much less those of domestic animals.

Few, perhaps, would argue against the altering of the bone marrow cells of a person with sickle cell anemia to enable him or her to produce normal hemoglobin, a technique by the way, which has not yet been developed. But suppose we were able to genetically slow down, or even halt the aging process, alter fetal cells to produce certain desired characteristics in babies, such as hair color or intelligence, or increase the strength in athletes, or alter our own physiology to enable us to breathe under water, or even clone individuals with certain unique talents. Who should decide what kinds of changes are acceptable and who should be allowed to have their genes or those of their children altered? And what if something goes wrong with the procedure and a defective human is produced? These questions are not easy and the techniques are not without hazard.

Regarding genetic engineering:

(These questions are also given in Exercise 18 in your workbook.)

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E-mail instructor: Sue Eggling

Clackamas Community College 2001, 2003 Clackamas Community College, Hal Bender

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Genetic Engineering - Clackamas Community College

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