Biotechnology: Principles and Processes

Biotechnology is the use of living organisms (or their parts, like cells and enzymes) to make useful products and services for humans. Humans have used a simple form of biotechnology for thousands of years — for example, using yeast to make bread and microbes to make curd. But modern biotechnology is much more powerful because it can change the very genes of an organism.

The heart of modern biotechnology is genetic engineering, also called recombinant DNA (rDNA) technology. This means changing the genetic make-up of an organism by adding, removing or altering specific genes. A piece of useful DNA from one organism can be joined to the DNA of another, creating recombinant DNA. An organism that has received a foreign gene in this way is called a genetically modified organism (GMO) or transgenic organism.

Why is this so useful? Because it lets us give organisms new, desirable traits — for example, putting the human insulin gene into bacteria so they make human insulin for diabetics, or putting a pest-resistance gene into crops. Modern biotechnology has two core techniques: genetic engineering (creating recombinant DNA and GMOs) and the large-scale growth of cells/microbes in big vessels called bioreactors to make the product in useful amounts. Together these have transformed medicine, agriculture and industry.

To cut, join, copy and move genes, scientists use a set of special biological tools. The three most important groups are enzymes, vectors and host cells.

• Enzymes — molecular 'tools' that act on DNA:
  • Restriction enzymes are the "molecular scissors" that cut DNA at specific sequences. Because they cut at particular sites, a gene of interest can be cut out precisely.
  • DNA ligase is the "molecular glue" that joins two pieces of DNA together (it seals the cut gene into the vector).
• Vectors — carriers that take the foreign gene into a host cell. The most common are plasmids (small, circular pieces of DNA found in bacteria, separate from the main chromosome) and certain viruses. A good vector can replicate inside the host and usually carries a marker so that cells which took up the gene can be identified.
• Host cell — the living cell (often the bacterium E. coli) into which the recombinant DNA is put; here the gene is copied and expressed.

So restriction enzymes cut the DNA, ligase joins the desired gene into a plasmid vector, and the vector carries it into a host cell — these tools together make gene manipulation possible. The same enzyme that cuts the gene of interest is used to cut the vector, so that their ends match and can be joined.

Putting the tools together, recombinant DNA technology follows a logical series of steps to make and multiply a desired gene:

1. Isolating the DNA — the DNA containing the gene of interest is extracted from the source organism's cells.
2. Cutting the DNA — restriction enzymes cut out the desired gene, and the same enzyme cuts open the vector (plasmid), so their ends match.
3. Joining (ligation) — DNA ligase glues the gene into the plasmid, forming the recombinant DNA.
4. Inserting into a host — the recombinant plasmid is put into a host cell (often E. coli); the cell takes it up (transformation).
5. Multiplying (cloning) — the host cell, grown in a culture, divides again and again, and every daughter cell carries a copy of the gene. Making many identical copies of a gene (or organism) is called cloning. Grown on a large scale in a bioreactor, the cells can make large amounts of the gene's product.
6. Obtaining the product — finally the desired product (such as a protein/medicine) is extracted and purified — this last stage is called downstream processing.

A separate but related tool is the Polymerase Chain Reaction (PCR), a technique that makes millions of copies of a specific piece of DNA quickly in a test tube. PCR is widely used in research, in diagnosing diseases and in forensics. Together, these processes let scientists produce valuable proteins, modify crops and study genes — the practical power of biotechnology.

In short, the standard steps of genetic engineering are: isolation of the DNA, cutting it with restriction enzymes, amplification by PCR, gene transfer of the recombinant DNA into a host cell, and finally the expression of the gene so that the host makes the desired product.