6.4: Nucleic Acids
Structure of RNA and DNA
DNA is an acronym (rather than a chemical formula) for d eoxyribo n ucleic a cid. It stores the genetic information for an organism and also passes that information to the next generation. RNA is r ibo n ucleic a cid and it is used as a template for the production of proteins based on the genetic information. The similarity between the names ribonucleic acid and deoxy ribonucleic acid reveals a similarity of their structures. We will first examine the similarities, followed by the differences.
Both DNA and RNA have backbones made of alternating sugar and phosphate groups. In the diagram of DNA below, the phosphate groups are highlighted in yellow and they are bonded to the sugar groups highlighted in orange. Notice that these form a chain or polymer down the left and right sides of the image.
Credit: DNA chemical structure by Madeleine Price Ball.
Connected to the backbone at each sugar group are bases. The four bases in the picture above can be grouped into two categories: adenine (A) and guanine (G) have a double ring structure whereas thymine (T) and cytosine (C) have a single ring structure. All of the bases have several N - H bonds and can participate in hydrogen bonding (there are also polar C=O groups on some of the bases). This hydrogen bonding holds the two strands of DNA together. Specifically, A and T always H-bond with one another (sharing two H-bonds) and G and C always H-bond with one another (3 H-bonds). Because of differences in their structures, other pairings of these four bases are not possible.
There are three differences between the structures of DNA and RNA:
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The sugars in the backbone of DNA and RNA differ by one oxygen atom. The deoxy- prefix in DNA indicates that the sugar is like ribose, but with one less oxygen atom.
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DNA is double stranded but RNA contains only a single strand
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In addition to the bases adenine (A), guanine (G), and cytosine (C) which are found in both DNA and RNA, DNA contains the base thymine (T) whereas RNA contains uracil (U).
Processes Involving DNA and RNA
DNA replicates itself within cells (makes another copy of itself). In addition, DNA is used as a template for the synthesis of mRNA which is used as a template for the creation of proteins. So, the main purpose of DNA in your body is to store the information that is ultimately used to make the proteins that serve a wide variety of functions throughout the body.