The Gene Tool Box
People who suffer from genetic diseases often feel a hopelessness that most people can’t fully appreciate. You can’t be cured from genetic diseases. If you have one, typically you’re born with it and you suffer with it all your life.
The difficulty is this: genetic diseases are caused by problems with a person’s DNA, and generally speaking, a person’s DNA remains fixed throughout life. Thus the sense of hopelessness.
But does it have to be this way? Recent advances in biotechnology suggest perhaps not.
For example, take beta thalassemia, a blood disorder that produces symptoms ranging from stunted growth to low energy to nausea. In its most severe forms, it requires monthly blood transfusions. The problem is found in the gene for the beta hemoglobin molecule—when it is defective, the blood cannot carry as much oxygen as the body needs. However, recent clinical trials indicate that it is possible to add a normal copy of the beta hemoglobin gene to defective blood cells, and thus potentially cure such sufferers for life.
This is one recent example of the promise of biotechnology. We also now have the ability to characterize a person’s genes, producing what has been called a “genetic fingerprint” for the individual. This technology has given crime scene investigators a new tool, helping to convict criminals and exonerate the innocent. It has also helped us verify family relationships (e.g., in paternity trials and in identifying human remains), and it has led to the development of new tests to diagnose a large number of genetic diseases.
Like all human endeavors, biotechnology needs to be guided by ethics, which in this case can be complex. But already this technology has produced many outcomes that everyone agrees are beneficial and ethically sound: new drugs, new forensic tests, diagnoses of inherited diseases, and valuable information about the human genome—to name just a few.
But how exactly have we been able to make such amazing advances?
Scissors and Glue
The answer lies in the myriad of molecular-level “tools” that God has built into creation at the genetic level. Genes are found in all living cells. They are the fundamental units of inheritance. Parents pass their genes on to the next generation, causing children to share their features.
Genes are carried on chromosomes, which in turn are made up of DNA molecules. The DNA itself is constructed from four building blocks, often designated by their abbreviated names: A, T, G, and C. The order of these building blocks composes the genetic code, which determines how individual genes function. Slight variations in the genetic code cause the physical differences we see among people (e.g., hair color, eye color, etc.) as well as genetic diseases (e.g., thalassemia).
At this level of creation we’ve discovered some amazing molecular tools, which in turn have led to a revolution in biotechnology.
The first are chemicals called “restriction enzymes.” These chemicals are produced by bacteria to fight off viruses. Normally, if a bacterium (which is a single living cell) is infected with a virus, the virus reproduces inside the bacterium until there are so many viruses that the cell bursts and the bacterium dies. But if the bacterium produces a restriction enzyme that recognizes a specific DNA sequence of the invading virus, it can cut that DNA at that location, rendering the virus harmless. It’s not unlike cutting the cord on power saw, or disconnecting the fuel line in a car.
Since the 1970s, scientists have been using restriction enzymes harvested from bacteria to cut DNA at specific sites, and another enzyme called ligase (also made by bacteria) to “glue” two pieces of DNA together.
With the discovery of these two tools, scientists were able to create the first examples of “recombinant DNA,” DNA molecules from two different sources spliced together to form one molecule. This has allowed scientists to make “custom” DNA molecules. For example, a drug to prevent blood clotting was developed this way. A normal gene for an anti-clotting protein was spliced together with a gene that controls milk production, and this new molecule was inserted into the goat genome. When this custom DNA is present in an adult female goat, she produces milk loaded with the anti-clotting factor, which can easily be extracted and processed into a drug.
Portable Photocopier and Switches
Another molecular tool we’ve discovered is a group of molecules called vectors, which are a combination DNA photocopier and shuttle: They can replicate a specific piece of DNA within a host cell, and also carry that new piece of DNA into another cell. This tool has helped genetic engineers produce various proteins within bacterial cells. This led to the creation of a novel form of insulin (“Humulin,” the brand name for “human insulin”), the hormone that is often defective in diabetes. It has also been the basis for creating all kinds of genetically modified organisms, such as virus-resistant crop plants and goats that produce pharmaceutical products. Vectors are also used in gene therapy treatments to carry a good copy of a particular gene into the cells of people whose bodies need them.
Then there are various types of molecular switches, like the lac Operon. This is an “on/off switch” that bacteria use to sense the presence of a particular food source (lactose) and to turn on the genes needed to process it. This molecular switch is often used in recombinant DNA molecules to activate a particular gene.
One of the newest types of molecular switches to be discovered has led to a whole new sub-discipline of biotechnology called optogenetics. In this case, single-celled algae respond to light by opening or closing channels in their cell membrane. Similar channels exist in nerve cells, but in nerves the channels are opened and closed by small changes in electrical current. Now biologists are studying nerve cell function using nerve cells that have the light-activated channel controls from algae genetically engineered into them. This modification allows scientists to precisely activate individual nerve cells with brief flashes of light.
These examples provide just a glimpse of how molecular biologists have used elements of creation designed by God for one purpose, to accomplish amazing and beneficial outcomes for suffering human beings. There is an almost endless list of such molecular components, and this list grows almost daily. The only limits seem to be human creativity and the raw materials God has designed, and so far neither has been a constraint. God certainly had a primary plan in mind when he designed such things as vectors and molecular switches, but knowing that he also foresaw their use in biotechnological applications gives me a deeper sense of the sacred in this area of human endeavor.
Rodney Scott, PhD, is associate professor of genetics at Wheaton College.
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