RNA is often simply defined as single-stranded, without question as to the fate of all of the potential hydrogen bonding sites along the bases of the strand. Consequently G/C rich regions of DNA are known to be particularly stable (see above). G-C pairs share three hydrogen bonds while A-T/U pairs share only two. So technically one “DNA molecule” consists of two separate molecules connected only through intermolecular forces. It is these highly-specific intermolecular interactions that allow for the ability of DNA to be “read” and “written” based on the complementary interactions. These are dehydration synthesis reactions, similar to the ones performed to make protein polymers from amino acid monomers or starch polymers from sugar monomers.ĭNA exists as two strands aligned antiparallel to one another and connected by many hydrogen bonds between the bases on the opposing strands. To form a DNA or RNA polymer, the 5’ phosphate of the incoming monomer forms a bond with the 3’ hydroxyl of the previous nucleotide to form the sugar-phosphate backbone (see the far left or right of the diagram at right). In DNA and RNA, the phosphate bonds to the oxygen attached to the 5’ carbon, also known as the 5’ hydroxyl (-OH) within a nucleotide. Guanine and adenine are purines (named for their double ring structure) while cytosine, thymine, and uracil are pyrimadines (for their single ring structure). The fourth base in DNA is thymine (T) and the fourth base in RNA is uracil (U). DNA and RNA share three bases: adenine (A), guanine (G), and cytosine (C). Sugars are numbered from the most highly functionalized carbon (so the carbon bonded to both an oxygen and the nitrogenous base in the DNA example above) starting with 1, where these carbons are referred to as 1’ (one prime), 2’ (two prime), etc. In DNA and RNA, the sugar is a ribose (hence collectively they can be referred to as ribo nucleic acids), which is a 5-carbon sugar that forms a pentagon shape (pentose). All nucleic acids are comprised of three structural components: a sugar, a phosphate, and a nitrogenous base (a structure containing nitrogen
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