The DNA Quadruple Helix or Tetrad DNA
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The DNA Quadruple Helix or Tetrad DNA
The DNA quadruple helix, otherwise known as the tetrad DNA is the newly discovered DNA in human cells, which is four stranded. A team of scientists made the discovery from Cambridge University, the same group that described the chemical make-up of human genome using the double helix DNA sixty years ago. The quadruple helix is also known as G-quadruplexes because they form in the Guanine rich region of the DNA (Amos Web). Guanine is a chemical base encoding genetic information and is abbreviated ‘G’; thus, the name G-quadruplexes. The helix is different from other helical DNA structures because it has four strands while others have two. The discovery of the quadruple helix in the cells may be significant in fighting cancer.
Initially, the quadruple helices were synthesized in the lab as computational and hypothetical models. However, using fluorescent biomarkers, they have recently been found to occur naturally in human cancer cells. The G-quadruplexes form when four Guanine bases interact and form a square in telomeres and chromosomes. Their structure is transitory in nature and appears in abundance when cells are about to divide. Cancer cells divide fast and have defective telomeres, and the helix may be unique to oncogenes. Consequently, the discovery will create new leads in developing cancer therapies that will not be harmful to other body cells (Walia Web). The therapies will help curb the multiplication of cancer cells by utilizing synthetic elements to contain the complex DNA structures because they will selectively target the fast-multiplying cells. The molecules will block cell division preventing cells from further replication.
Other forms of DNA vary from each other based on the structure of their helices. The most common and conventional model used to define the genetic code of the human genome is the double helix or the B form, which is right-handed. In 1953, James D. Watson and Francis Crick discovered the double stranded DNA. The helices intertwine with each other forming two grooves, major and minor, of varying widths. The grooves are significant in binding proteins with the bases. The helices also turn every 3.4nm with 10 base pairs per turn because the distance between two base pairs is 0.34nm. The other form of DNA structure is the A form, which occurs when conditions change such as increased salt or alcohol concentration. This structure is also right-handed, but it turns every 2.3nm with 11 base pairs in every turn. The third form of DNA structure is the Z form, which has a zigzag appearance and is left-handed. It turns at 4.6 nm with 12 base pairs per turn. DNA molecules with this structure are those with alternating G-C sequences in high salt or alcohol solutions (Nordlund 121).
The three forms of the double helix DNA structure differ from the G-quadruplexes in the number of helices. The former have two intertwining strands while the latter has four strands intertwining to form a square structure. Another difference is that the double helix structures have all the four bases, Adenine, Guanine, Thiamine, and Cytosine on the strands while the G-quadruplexes has only Guanine. The G-quadruplexes are mainly confined to fast-replicating cells such as cancer cells, but the other forms are found in any cell in the body (Walia Web).
The discovery of these G-quadruplexes in fast replicating cells has created the perfect platform in the war against cancer. Scientists hope to utilize the unique DNA structures to defeat cancer by targeting tumor cells. Unlike the double helix DNA structures, the four-stranded DNA structure mainly occurs naturally in cancer and tumor cells. The unique molecules will be significant in developing therapies that specifically target cancer cells. This will make it easy to treat cancer without harming other cells.
Works Cited
Amos, Jonathan. ‘Quadruple Helix’ DNA Seen in Human Cells. BBC News, Jan. 2013. Web. 25 Oct. 2013.
Nordlund, Thomas. Quantitative Understanding of Biosystems: An Introduction to Biophysics. Boca Raton: CRC Press, 2011. Print.
Walia, Arjun. Scientists Discover Quadruple Helix: Four Strand DNA in Human Cells. Collective Evolution, July 2013. Web. 25 Oct. 2013.
