Insight into the Blueprint for Human Life

Until the beginning of the 1940s very little had been known about heredity. What was known was that certain traits were inherited from the mother and father and passed on to the children. The particles responsible for this transmission of heredity were called genes.
But what genes are made of and what they look like remained unexplained for a long time.

However, then the American researchers George Beadle and Edward Tatum discovered that genes direct the production of proteins, and the proteins in turn are responsible for the development of traits (e.g. body size, hair color, shape of the nose, etc.).
In 1944 the chemist Oswald Avery proved that DNA was responsible for heredity – a substance that is composed of sugar, phosphates, and four so-called bases.
Nevertheless, most of the scientists were still skeptical. It was not until eight years later that the consensus changed. DNA was declared to be the hereditary substance. Now an unprecedented race began to find out as fast as possible what the hereditary substance actually looked like.

In 1951 the x-ray expert Rosalind Franklin was successful in making the first structural x-rays of DNA. They were pictures consisting only of points, but the arrangement of the points delivered significant information about what DNA could look like.
Cambridge (England) – 1953. The two young scientists, James Watson and Francis Crick, saw the structural x-rays made by Rosalind Franklin, and more and more, their thoughts revolved around the topic of DNA. They decided to solve the puzzle of the structure of DNA by constructing a model using pieces of cardboard and building blocks. As they moved these back and forth it suddenly became clear to them how the building blocks had to be connected to each other so that all of the information from the structural x-rays would fit into the puzzle.

Deciphering the DNA Code

What they found was that the DNA looks like a sheer endless, twisted rope ladder. The ropes of the ladder are made of a sugar alternating with a phosphate acid. The rungs of the spiral ladder consist of four chemical substances which are called bases. These bases are named A = adenine, T = thymine, C = cytosine, G = guanine.
It soon became evident that this chain of four bases contains a code for producing all of the building blocks of the body. Twelve years later the code was deciphered successfully. Groups of three bases each give an instruction designed for the cellular protein factories. For instance, the instruction of the triplet code "AGT" reads as follows: "Take the component called serine and tie it to the end of the building block chain which is presently under construction." Then additional codes follow and the building blocks are thus assembled one after the other to form a protein. Finally, a code word has its turn which gives the following signal to the protein factory: "The protein is now finished."

The cell's protein factories – the so-called “ribosomes” - move along the chain of gene letter (represented by colored rods). According to the instructions encoded with gene letters on the strand they assemble one building block after the other to form a chain of amino acids (represented by a chain of colored balls).
(picture: InformationsSekretariat Biotechnologie, modified)

Deciphering the Human Genome

Since the middle of the 1960s it has been known how genetic information is stored in the DNA and what the blueprints for the proteins look like. However, our body is made up of thousands of different proteins. To be able to read the complete blueprint of the body, one must know the sequence of all the bases in the DNA chain.
That is why in 1988 scientists decided to analyze the DNA chain one building block at a time or rather, one base at a time. The international publicly funded Human Genome Project (HGP) was the most ambitious research project at that time point. Using a chemical method, it is possible to determine whether the just dissected building block is an A, T, C, or G. Thus, one genetic letter after the other can be "read" in the DNA. This process is called sequencing of the DNA. Ten years later Craig Ventor, the director of the pharmaceutical company Celera Genomics, decided to decipher the human genome, too. In the spring of 2001 both competitors reached the goal at the same time. They finished mapping the exact sequence of the 3.2 billion gene letters and from that were able to read approximately how many genes are contained in the human hereditary material. A surprise: each human has approximately 20,000 to 25,000 genes. That’s only about twice as many genes as a fly has! Scientists had expected considerably more genes in human DNA.

The follow-up project of HGP was launched in September 2003: The Encyclopedia Of DNA Elements (ENCODE) has the scientific goal to identify the precise position of all human genes and other functional elements in the human genome sequence. Those determine for example the structure of chromosomes or regulate the transcription. This knowledge is the prerequisite for the prediction of potential disease risks or for the development of new therapies.
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