For thousands of years, people have exploited the biochemical activities of living cells. Breadbaking and beer-making, for example, depend upon the ability of microscopic yeast cells to convert sugars to carbon dioxide and ethanol (ordinary alcohol). Cheese- and yogurt-making also depend on the activities of single-celled life forms—microorganisms.
Every microorganism is a tiny factory, capable of carrying out basic biochemical functions. Biochemical knowledge has grown dramatically in the past few decades, providing the basis for a new industry—biotechnology.
An enzyme is an organic catalyst a protein substance that speeds up a chemical reaction, normally within plants and animals. Throughout the reaction, the enzyme itself remains unchanged. Simple examples of the use of enzymes outside their natural environment include fermentation—the gradual chemical change of a substance, such as a carbohydrate, through the action of yeast. Yeast fermentation (as in making beer) occurs due to the presence of a series of enzymes in the yeast cells. This catalytic activity of an enzyme does not depend on its being inside a cell, however. Many enzymes produced naturally by microorganisms exist outside cells. For example, they may be released from the cell into the surrounding medium. There, the enzymes break down some of the substances in the medium into molecules. The cell can then absorb these molecules as food.
Many different enzymes have now been isolated as pure substances. Some are produced on a very large scale, usually in a relatively crude form for use as industrial materials. Detergents today often contain “biologically active” ingredients. These are enzymes intended to improve the efficiency of the product by biodegrading insoluble materials, such as protein. Such materials make up part of the dirt on clothing.
Enzymes are also used in various ways in food manufacture. For example, one method of making a chocolate with a liquid center is to start with a solid center. Then an enzyme is added, which liquefies part of the solid content after the chocolate surrounding it has hardened.
The area of biotechnology that has attracted the most attention in the past decade is genetic engineering. Partly as a result of developments in enzyme biochemistry, it is now possible to perform a variety of operations on nucleic acid polymers. These substances, composed of many molecules, form the genetic inheritance of a cell.
DNA contains a number of different genes. Each of these genes contains a code for the manufacture of a particular protein. It is now possible to cut the nucleic acid polymer and splice in extra genes not normally found in the microorganism. The organism’s genetic code is thus altered and its growth follows the new pattern in its genes. Provided that conditions can be found to make the organism “express” these foreign genes, large quantities of specific proteins can be made.
An example in which this technique can be applied usefully is in the manufacture of insulin. This hormone must be taken regularly by large numbers of diabetics whose pancreas is unable to manufacture it naturally. The pancreas is a gland located behind the stomach. The insulin supplied to diabetics is obtained mostly from pig pancreases by a process of extraction and purification.
Microorganisms do not normally produce insulin. But the insulin gene can be inserted into bacteria. These are then cultured (grown) to produce insulin. Although most diabetics can tolerate pig insulin, some have an adverse reaction. This is possibly due to its structure being slightly different from that of human insulin. Insulin made by genetic manipulation of bacteria, however, is chemically identical to human insulin. It therefore overcomes the problem of intolerance and the body is normally able to use it. A further advantage is that culturing of microorganisms as an industrial process is easier to control than producing insulin from animal glands. In the latter case, problems of continuity and quality of the raw material can arise.
Products such as insulin are very valuable to those who depend on them. It is therefore possible to recoup the high cost of research and development involved in establishing a genetically engineered process. Nevertheless, there have been some attempts to introduce biotechnological processes for less costly products. These generally need to be produced on a larger scale.
Protein is an important dietary ingredient. Processes are now available that make it possible to produce large quantities of protein-rich microbial cells as feedstuffs for farm animals. Such processes require far less space than is needed to produce the same amount of protein from green plants. For example, about 80,000 tons (70,000 metric tons) per year of bacterial protein can be produced in a factory covering only a few acres. Methanol (made from natural gas) and ammonia are used as the raw materials.
Over the next few years, it is likely that an increasing number of high-value products will be produced biotechnologically. These will come not only from microorganisms but also from large-scale fermentation of both animal and plant cells. Until recently, it has been difficult to maintain cultures of cells from multicellular organisms in a healthy state for long periods. Modern developments in biochemical techniques have now made this possible. New vaccines and important, complex organic molecules could be produced in these ways. In the longer term, biotechnology holds out the hope of producing commodity materials, such as plastics, by fermentation directly from living organisms. This method would free us from dependence on diminishing supplies of oil.