DNA consists of two strands, each composed of certain sugars and phosphates. The two strands wind around each other in a spiral, much like the two sides of the ladder wind around each other. Linking the two strands together are certain chemical elements called amines or bases arranged in a particular pattern. The rungs of the rubber ladder would be like these chemical links," (Ciccarelli p.252).
An understanding of DNA is a fundamental necessity in understanding what it is that makes us who we are. Not the acts which we commit, but really who were imbedded in the core of ourselves. Ultimately, the genetic design of us as human beings is what truly the history book is as it comes to humans and what makes them who they are. Structural DNA is described as, "Some regions of chromosomes remain highly condensed, tightly coiled, and untranscribed throughout the cell cycle. Called constitutive heterochromatin, these portions tend to be localized around the centromere, or located near the ends of the chromosome, at the telomeres," (Johnson p.387).
After Rosalind Franklin's use of x-ray technology as it came to DNA, the world would be introduced to two gentlemen by the names of James Watson and Francis Crick. "Learning informally of Franklin's results before they were published in 1953, James Watson and Francis Crick, two young investigators at Cambridge University, quickly worked out a likely structure for the DNA molecule (figure 14.10), which we now know was substantially correct. They analyzed the problem deductively, first building models of the nucleotides, and then trying to assemble the nucleotides into a molecule that matched what was known about the structure of DNA. They tried various possibilities before they finally hit on the idea that the molecule might be a simple double helix, with the bases of two strands pointed inward towards each other, forming base-pairs,"
Elaborating further that, "In their model, base pairs always consist of purines, which are large, pointing toward pyrimidines, which are small, keeping the diameter of the molecule a constant 2 nanometers. Because the hydrogen bonds can form between the bases in a base-pair, the double helix is stabilized as a duplex DNA molecule composed of two antiparallel strands, one chain running 3' to 5' and the other 5' to 3'. The base pairs are planar (flat) and stack 0.34 nm apart as a result of hydrophobic interactions, contributing to the overall stability of the molecule," (Johnson p.287).
"The Watson-Crick model explained why Chargaff had obtained the results he had: in a double helix, adenine forms two hydrogen bonds with thymine, but it will not form hydrogen bonds properly with cytosine. Similarly, guanine forms three hydrogen bonds properly with thymine. Consequently, adenine and thymine will always occur in the same proportions in any DNA molecule, as will guanine and cytosine, because of this base-pairing," (Johnson p.287).
Just as any scientist needs to do in order to prove their theory; Crick and Watson set out to do just that. "In late February of 1953, Crick and Watson built a model out of tin established the general structure of DNA. This structure explained all the known chemical properties of DNA, and it opened the door to understanding its biological functions. There have been minor amendments to that first published structure, but its