The sense of growth of DNA
In vitro DNA synthesis
Kornberg, a disciple of the biochemist Severo Ochoa, studied in 1956 how a new complementary strand of DNA was synthesized from another strand, and which enzyme regulated replication. He isolated the DNA polymerase enzyme from Escherichia coli bacteria, and found that it is capable of synthesizing DNA in vitro.
The DNA polymerase requires deoxyribonucleotides -5-triphosphates adenine, thymine, guanine and cytosine, magnesium ions Mg2+, and that one of the chains of the DNA molecule made of "pattern" and an end acting as "primer”.
The DNA polymerase is an enzyme consisting of about 1000 amino acids, and is located in the nucleus and in the mitochondria. This enzyme binds the standard DNA, the primer DNA, and the nucleotide to be added. It can synthesize DNA from natural DNA in vitro (not in a living cell).
The DNA polymerase can not start the synthesis of a chain, but can only add nucleotides to the end of a chain preexisting, the DNA primer. It only adds the nucleotides at the end of the chain that the 3 'carbon of the nucleotide has free.
Thus, the strand that begins with the primer DNA only grows in the 5'→3' direction. Thus, the nucleotide that has its free 5' carbon is the first nucleotide of the DNA chain and the nucleotide that has free its 3' carbon is the last nucleotide that has been added to the chain, and to which another can be added.
The new synthesized chain is antiparallel and complementary.