Genetic Engineering is in fact, pretty darn great. Basically, genetic engineering means that the DNA (DeoxyriboNucleic Acid) material of any source (living or dead cell) can be isolated, identified, altered, and introduced into the chromosome (DNA) within any living cell. Most of the work involves isolation and identification of genes - the components within DNA (chromosomes) which contain ALL of the information for the synthesis of everything in every living cell (see What the Heck is a Gene?). The information in a gene is a code - which is a three letter-at-a-time sequence of deoxyribonucleotides (A - adenine; T -thymidine; C - cytosine, or G - guanine). The information in this code (the "sentence" may be thousands of "letters" long) is relayed by a messenger. This intermediate messenger is called messenger RNA (mRNA). There is an enzyme which "reads" the DNA and makes this special kind of RiboNucleic Acid from it. This mRNA then travels to the special machinery inside the cell, called a ribosome, and there the message is translated (like translating a foreign language). The translation of mRNA leads to the synthesis of a protein - this protein may be one of the thousands of enzymes necessary for cell life, or, it may be one of the thousands of proteins involved in transport of nutrients, or the structural parts of the cell.
Now, every gene in the chromosome has regions which "say" to the enzyme responsible for "reading" the DNA, and converting the code to mRNA, to Start Here to make the message (mRNA) and End Here (stop making the message). And also, there are regions within the gene which end-up as a code in mRNA which "say" to the ribosome, Start Here making the protein, and End Here making the protein. Every organism has a little different gene structure for the message-making enzyme of that species - so - the enzyme in human cells that makes mRNA from human gene DNA, cannot "recognize" the gene in a bacterium, and therefore cannot relay a message - and vice versa. Further, the mRNA regions which "converse" with the ribosome can only do so if the mRNA and the ribosome are from the same organism (even viruses are sort of like this... a virus which works in human cells, usually will not work in bacterial cells).
Now, genetic researchers have investigated gene structure for many, many years - and have identified these important regions - know exactly the sequence of animal, plant, and bacterial genes, and the regions which allow the gene to be expressed (mRNA made from it). Genetic engineering allows one to actually change the sequence of the DNA at these important regions to allow a human gene for example, to be expressed by bacterial enzymes and ribosomes. So, if one can get this gene into the chromosome of a bacterium, even though the gene encodes information for a human protein, if one alters certain of the gene regions to make these regions compatible for bacterial enzyme interaction, then this human gene will be expressed in a bacterium, and a human protein can be made in this way.
The bacterium usually used for introduction of foreign genes, is a very special laboratory strain of Escherchia coli (E. coli). This strain is a real wimp (requires special nutrients), and cannot survive outside of the laboratory (purposefully changed for safety reasons). Because of this ability, genes for certain human substances have been introduced into E. coli. This process of gene introduction into a cell is called gene "cloning." Since bacteria divide every 20 minutes or so, the gene will be cloned within the entire population (same gene in every single bacterial cell - millions of copies therefore of this gene within the entire population) - therefore, one can get many millions of bacterial cells, each of which are making this human protein. This protein can then be produced in great quantity, isolated, purified, and given to people who need it. Here are two examples: human insulin, and human erythropoietin.
Both human insulin and human erythropoietin are very hard to isolate from humans - very, very tiny quantities are made at any one time - are each powerful hormones). We'll look at insulin first.
Many diabetics cannot make insulin and therefore need an external source of this substance (not so for all diabetics - there are different kinds of diabetes). In the past, since human insulin could not be isolated very readily, diabetics injected either pig or cow insulin (the structure of insulin among pigs, cows, and humans is almost identical). But by cloning the gene for human insulin into E. coli, plenty of human insulin (the "right stuff") is available now to save people's lives. As for erythropoietin, this hormone is required for human red blood cells (erythrocytes) to mature to a functional red blood cell (without these erythrocytes we would not be able to use the oxygen we breathe). Some people cannot make this hormone. However, by cloning the gene for erythropoietin into E. coli, this hormone is readily available, and is now saving many lives.
Further, there are people trying to clone the gene from bacteria which is responsible for production of an enzyme which converts atmospheric nitrogen (N2) to ammonia (NH3), into plants. All nitrogen in our bodies comes from ammonia - but - the ONLY organisms which make ammonia from atmospheric Nitrogen, are certain bacteria that live in a symbiotic relationship with plants called legumes (pea plants - a redbud tree is really a great-big pea plant). If it weren't for these particular bacteria, and their symbiotic relationship with legumes, no life as we know it would exist on earth. So, people would like to clone this gene into many kinds of plants other than legumes.. that way, ammonia wouldn't need to be added to soil in order for plants like corn and wheat to grow - the corn and wheat could make all of the ammonia they needed - on their own. Thus, many starving people in the world would have more food. Now, here are a few bits of extra information.
A symbiotic relationship means that different organisms get together, and each sustains the life of the other. The bacteria which convert N2 to NH3 are in the soil, and they form little colonies within the root-hair cells of the pea plant (legume). The presence of these bacteria within the plant roots activates a system in the plant cells which leads to the production of little nodules which surround the colonies of bacterial cells. Further, the plant also responds by making what is called legume-hemoglobin. That's right! - pea plants make a kind of hemoglobin - sort of like our own hemoglobin. This legume-hemoglobin protein holds onto Oxygen, much like our own hemoglobin does - and in doing so, any oxygen is prevented from reaching the enzyme the bacteria make which converts N2 to NH3 (ammonia). If it weren't for this legume-hemoglobin, this enzyme could not work! So, the bacteria get protection and nutrients from the plant, and the plant gets ammonia from the bacteria. Pretty neat - huh? Well, lets go back to talking about genetic engineering.....
Certain human genes are being introduced into other humans who have a dysfunctional gene for a substance necessary for life. And, genes which make anti-cancer substances are also being cloned, and in some cases being introduced into the chromosomes of certain immune-system cells of a person, in order to help that person fight cancer. There are what are called, clinical trials, which are taking place at this moment - very focused efforts to try to save a life through genetic engineering.
So, genetic engineering is wonderful and powerful. But, like all wonderful and powerful things, there is a potential for mis-use. Therefore, it is every person's responsibility to become as informed as they possibly can in order to see that such things are used for the good of this planet... we are the caretakers of all that is here.. it is our responsibility to guard this precious earth and all of the living things on it.