DNA Base Pairs
Adenine, thymine, cytosine, and guanine are the four bases that comprise DNA. The bases always appear in pairs: Adenine with Thymine and Cytosine with Guanine in every instance. It is worth noting that in every living organism, the percentages of the adenine and thymine as well as cytosine and guanine are consistent regardless of where the DNA sample originated. The bases that appear with their accompanying bases are joined to the chain of phosphates by a collection of sugars known as deoxyribose. The outside strands are contorted as a part of the double helix characteristic of DNA, and that contortion helps to keep the bases connected to one another and to the phosphate chain. The phosphate chain locks the nucleobases in their place.
Adenine is one of the four nucleobases found in DNA molecules. It is also a purine (along with Guanine), which finds its partner base from a pyrimidine, in the DNA example Thymine. In DNA molecules, Adenine forms a covalent bond with Thymine (Uracil in RNA), as well as Nitrogen and Hydrogen to strengthen the bond between these bases. Protein synthesis is the primary job of Adenine in DNA molecules.
Also known as 5-methyluracil Thymine, a pyrimidine, bonds with Adenine in DNA. It is worth noting that Thymine is not present in RNA (replaced by Uracil). Thymine benefits from the addition of Hydrogen and Nitrogen to the bonds. Like the other three nucleobases, Thymine retains and stores information as its primary function.
A triple-Hydrogen bond shared with Guanine is an identifying characteristic of the nucleobase Cytosine. This nucleobase is a pyrimidine that is partnered with another purine to balance to the two sets of pairs in DNA. Cytosine has an unpredictable pathology and routinely changes to Uracil eliciting a response from the self-repair function of DNA.
The final nucleobase is Guanine. Guanine is a purine (that bonds with Cytosine) in both DNA and RNA molecules. Guanine is a very Oxygen reactive compound and has a very high melting point (350 C). Like the other three chemicals in DNA molecules, Guanine has a primary role of information retention and storage.
DNA Molecule Structure
The base pairing of Adenine to Thymine and Cytosine to Guanine allows for the DNA code to be carried out as cells divide. To complete this process, the DNA molecule separates so that only half of the coding information is available. The remaining enzymes then produce the opposite, missing halves of the DNA strands and the bonding to make sure that a new, identical strand is formed.
1. Zoom: top scene
Hot Spot: blue-net-tennis-court = DNA; Adam = adenine; pyramid-head-chicken-thigh-guy = thymine; Gandhi = guanine; pyramid-head-sightseer = cytosine
Learning: Because of DNA's double-helix structure, which is represented in this CoursePic by blue-net-tennis-court, base pairs are the measure of individual genes and even the whole genome of an organism. Base-pair units, pictured here as Adam for adenine with pyramid-head-chicken-thigh-guy for thymine and Gandhi for guanine with pyramid-head-sightseer for cytosine, comprise two nucleobases. These nucleobases are secured by hydrogen bonds, which are illustrated by Adam's blue bubbles drifting toward his tennis partner. Known as Watson-Crick base pairs, these nucleotides maintain the structure of both DNA and RNA, and serve too as a backup of genetic data.
Story: We hope the explosive tempers often observed during tennis matches don't flare up on the blue-net-tennis-court! Each player must follow the strict "Watson-Crick rules" in order to avoid the terrifying phenomenon of overlap repulsion. Luckily, Adam's got it together. He blows blue hydrogen bubbles to make a valid bond with his partner pyramid-head-chicken-thigh-guy. After all, the DNA structure's not going to maintain itself. Poor Gandhi has his hands full maintaining the three bonds with his scatter-brained partner pyramid-head-sightseer.
2. Zoom: bottom scene
Hot Spot: red-net-tennis-court = RNA; Adam = adenine; Uranus-pyramid-head= uracil; Gandhi = guanine; pyramid-head-sightseer = cytosine
Learning: Although RNA, represented by red-net-tennis-court, and DNA comprise the three bases guanine, cytosine, and adenine, only RNA contains uracil. Uracil is a pyrimidine like thymine and cytosine with a liquid/crystalline base that pairs with the purine adenine's larger, double-ringed chemical structure. It is represented by the Uranus-pyramid-head. All of these nucleotides are vital to cell functions such as metabolism, signaling, enzyme activation, and energy transfer, the last demonstrated here by the tennis players' back-and-forth exchanges. Various gene-binding proteins recognize specialized pairing patterns and must be vigilant about following strict Watson-Crick rules to ensure complementarity of form, and of hydrogen-bonding properties. Hence, adenine can pair with thymine and, in RNA, uracil, but not with cytosine and guanine. A big difference from DNA is that RNA is almost always a single-strand polynucleotide chain. Because RNA isn't actual genetic material, it doesn't employ itself as a template for self-replication. As represented by the red net, RNA is an intermediary between the gene and the protein-making machinery, shown as the tennis players.
Story: You may not, at first glance, notice much difference between this venue and the blue-net-tennis-court. However, a closer look reveals that the tennis powerhouse, the pyramid-head-chicken-thigh-guy, has been replaced by equally assertive, if somewhat spacey, Uranus-pyramid-head.