All living organisms, plants, animals, bacteria, and even some viruses, contain DNA. DNA is deoxyribonucleic acid, a molecule with two long chains that coil around each other creating a shape referred to as a double helix. Within the DNA is the material used for the genetic instructions of all life forms. DNA joins proteins, lipids, polysaccharides, and other nucleic acids as the four major macromolecules. These four macromolecules are found in all forms of life, and are necessary for life to exist.
Each of the two strands of DNA is known as polynucleotides and is made up of nucleotides. Each nucleotide is made up of deoxyribose, a sugar, a phosphate group, and one of four nitrogen-based nucleobases, cytosine, guanine, adenine, or thymine. These nucleotides are connected to each other in their famous chain shape by a series of covalent bonds. The bonds are formed by a sugar of one nucleotide sharing electrons with the following nucleotide’s phosphate. This creates an alternating pattern of sugar followed by phosphate. The separate polynucleotide strands join together at their nitrogenous bases by means of hydrogen bonds. These bonds are formed between the polynucleotide according to base pairing rules; adenine connects to thymine and vice versa, cytosine connects with guanine and vice versa.
As we mentioned earlier, DNA stores information that organisms need. The information is needed primarily to synthesize proteins, which sounds minor but that is basically a summary of your entire body’s metabolic process. However, a significant portion of organism’s DNA is non-coding. This means that the majority of molecules that make up the DNA do not contain information relevant to protein synthesis. These non-coding molecules make up 98% of human’s DNA!
What makes DNA even more interesting is that each of the two strands of DNA contains the exact same genetic information. This structure allows the DNA to be split down the middle and preserving the information stored in a process known as DNA synthesis, and it occurs naturally as well as artificially. When DNA is synthesized naturally, it appears in a process known as DNA replication. Artificially, DNA synthesis is achieved primarily through two methods: polymerase chain reaction (PCR) and gene synthesis (sometimes referred to as DNA printing).
These processes are distinctly different, and use specific catalysts to undergo the reaction. Here is some more information about DNA synthesis, PCR, and gene synthesis, and the catalysts that initiate these processes!
Each individual organism is composed of a system of organs, which are individually made up of tissues. These tissues are made up of cells, which are the “building blocks of life.” Cells have a much shorter life than tissues, organs, and thankfully organisms! But this causes a problem because for tissues to survive, the cells making up the tissues must survive. And if tissues die, organs die, and if organs die, organisms die.
Therefore, cells must be constantly replicating themselves in the cell cycle. This replication would be impossible if the cell didn’t have a way to transmit the genetic information it holds to the new cell. That’s where DNA comes in.
As we mentioned earlier, DNA’s structure allows for the molecule to be split directly down the middle without losing any information that the molecule originally contained. This gives cells the ability to take each DNA molecule and replicate it in a process known as DNA synthesis. With the replicated DNA, the cell can then divide and replicate. Without this process, life as we know it would not be possible and it occurs in all known organisms.
During DNA synthesis, the two individual strands are split down the middle by initiator proteins, or catalysts. The catalysts initiate the split at origins, specific point in the DNA that is receptive to the initiator proteins. These catalysts tend to be composed of adenine and thymine. The composition is because adenine and thymine are joined by a covalent bond of 2 electrons, as opposed to the three electrons in the covalent bond between cytosine and guanine. The fewer electrons shared in a covalent bond, the weaker it is. After the catalyst finds the origin, the proteins recruit other proteins and form the protein complex known as pre-replication complex. The pre-replication complex then separates the double helix.
After the DNA molecule is unwound, it moves on to the elongation phases, which adds 3 hydroxyl groups to the molecule. From there, the molecule is ready for the replication stage of DNA synthesis, which results in an identical DNA molecule.
Polymerase Chain Reaction
Polymerase Chain Reaction, most often referred to as PCR, is a biotechnical method of copying DNA. This process is the artificial equivalent of the previously described process of DNA Synthesis. It is one of the most popular methods of DNA replication in the biotechnical world, because it can use a single DNA sequence to create millions of copies. PCR is used in medical research, criminal forensics, and clinical laboratory research. It was invented in 1983 by Kary Mullins and Michael Smith, who both went on to be awarded the Nobel Prize in Chemistry for their work.
So, how does PCR work?
PCR is a machine that amplifies, or copies, DNA by first heating the DNA to about 94 degrees Celsius so that it unwinds into its two molecules. This process achieves similar results that the catalytic initiator proteins achieve in DNA synthesis.
After heating the DNA to separate the molecules, the solution is cooled to about 54 degrees. The PCR catalyst is then added. In this process, an enzyme called Tag Polymerase is used. The enzyme takes the information stored in a strand of the original DNA and binds to it.
Now, the PCR warms again to 72 degrees. The original DNA molecules are taken by the catalyst and undergo the process of elongation. Elongation takes the original DNA strand and creates a mirror image, creating two strands of DNA identical to the original.
The immediate result of this process is two new strands of DNA identical to the original. Each new strand is composed of an original strand and a synthetic strand. The process can then be repeated, creating 4 new molecules of DNA, then 8 new molecules, and so on.
Another method of synthetically replicating DNA is known as artificial gene synthesis, or DNA printing. The key difference between gene synthesis and other synthetic biological methods of DNA synthesis such as PCR and molecular cloning is that gene synthesis does not require an original DNA molecule. It is known as DNA printing, similar to 3-D printing objects, gene synthesis allows you to create a molecule that can be unique. The uniqueness of the printed genes allows for DNA molecules that have new gene sequences and varying sizes.
A common method of gene synthesis utilizes the catalyst Oligonucleotides. These are chemically synthesized together by assembling individual pieces of nucleoside phosphoramidites. Each phosphoramidites is added, one at a time, until the chain begins to grow. The resulting sequence is the opposite of its biological counterpart, but can still be useful.