The 1970's are witnessing a scientific breakthrough of potential significance, comparable to the splitting of the atom in the 1940's and the landing of human beings on the moon in the 60's. This new knowledge, known as recom
The 1970's are witnessing a scientific breakthrough of potential significance, comparable to the splitting of the atom in the 1940's and the landing of human beings on the moon in the 60's. This new knowledge, known as recombinant DNA research, enables man to combine the genes of unrelated species and introduce these hybrid genes into a live organism, where they become active.
Before examining the religious implications of this development, we will describe the continuing gene re combination experiments and the lively debate they have touched off among both scientists and nonscientists.
A characteristic property of living matter is its potential ability to re produce itself. The information required for faithful reproduction re sides in the chromosomes of the cells—the building blocks of living matter. This genetic information is divided into units called genes. Each gene contains a particular piece of specially coded genetic information regarding the structure either of a protein molecule or of a small ribonucleic acid molecule or of some control function in the biosynthesis of both nucleic acids and proteins.
Genes control all of the physical attributes of an organism by con trolling protein molecules—the molecules that perform most of the work within the cell, and constitute a large portion of its structure. During growth, the genes inside each cell double in number so that following cell division both resulting cells receive the identical number of genes. This holds true for all forms of living matter from the simplest to the most complex.
In the early 1940's O. Avery, of Rockefeller University, discovered that the chemical identity of genes was deoxyribonucleic acid, commonly abbreviated as DNA. De tailed structural analysis of this sub stance revealed that DNA ordinarily occurs as a double molecule—two very long molecules intertwined around each other in a "winding staircase" pattern. The genetic in formation carried by DNA is deter mined by the particular sequence in which the building blocks of DNA, the nucleotides, occur. The two strands making up DNA are not identical in their chemical make-up, but they contain identical genetic in formation, somewhat like the positive and negative plates of a photo graph.
As chromosomes double inside the cell prior to cell division the two strands of the DNA molecule separate and the original positive strand acquires a new negative strand. Likewise, the original negative half of DNA is joined with a newly made positive strand. In this fashion each new cell inherits the exact number of genes of the original, and the species' characteristics are perpetuated.
In nature it happens occasionally that extra pieces of foreign genetic material find their way into cells. However, cells are not defenseless against this intrusion. Each cell has a detachment of internal-security agents, known to scientists as restriction enzymes. (Enzymes are special protein molecules that pro mote specific chemical conversions.) The restriction enzymes carefully probe the structures of any newly arrived genetic material. If it turns out to be of foreign origin, the restriction enzymes rapidly degrade and inactivate it. The universal and ubiquitous presence of restriction enzymes is one of the main barriers between inter-species reproduction.
In the early 1970's molecular biologists discovered that restriction enzymes did not degrade foreign DNA molecules randomly, but broke the strands at very specific sites. In fact, these enzymes break one strand only at a particular nucleotide sequence that they are programmed to recognize; the second strand is cleaved at a different site not far removed. This attack on the foreign DNA converts the original, long, double-stranded DNA to several shorter pieces with identical frayed ends. These ends can fit each other in the manner of a jigsaw puzzle.
If these short pieces of DNA molecules are placed in a test tube and treated by appropriate chemical means, splicing of these units occurs. This crucial discovery gave rise to the field of recombinant DNA research. Scientists were quick to realize that if one takes two separate types of DNA, each treated with the same kind of restriction enzyme, and applies the splicing technique, the end products are hybrid DNA molecules.
Most DNA recombination re search to the present has involved Escherichia coll. This harmless microorganism, originally isolated from the human colon, is one of the most studied and best understood organisms. Scientists have learned that hybrid DNA is not degraded when introduced into special variants of E. coli which have defective restriction enzymes. Genes of foreign origin thus introduced can express themselves in the host cell.
As scientists began working with this system they realized that highly dangerous varieties of E. coli and other microorganisms might be produced by such techniques. For ex ample, if the gene that carries the codes for the neurotoxin of botulism in the organism Clostridium botulinum were to be spliced into E. coli we would have a truly deadly organ ism, since less than a millionth of a gram of botulinum will kill a person.
Consequently a number of concerned scientists published a plea in the Proceedings of National Academy of Sciences to halt these kinds of experiments. Later a conference composed of 140 scientists from 16 countries convened in Asilomar, California, for the purpose of discussing guidelines in this type of work. Not everyone agreed on the magnitude of the danger involved, but there was no doubt in anyone's mind that definite risks were involved. The conference agreed to formulate guidelines for recombinant DNA research by which the potential risks would be matched by appropriate containment measures. Unfortunately, the magnitude of danger involved is