Saccharomyces cerevisiae (Baker's yeast)
Deoxyribonucleic acids (DNA) and ribonucleic acids (RNA) use the same basic chemical building blocks: sugar and phosphate for the backbone and bases attached to the sugar. The structure of DNA had been found through model building based on the X-ray diffraction of DNA fibers in the early 1950s by Crick and Watson. Detailed X-ray structures of DNA fragment crystals later confirmed their initial proposed model: that of a double-stranded helix. Somewhat later the first structures of proteins became known. It took however until the 1970s before the RNA structure was published. RNA differs most prominently from DNA by a small but significant detail. Where DNA has a hydrogen atom attached to one particular sugar atom, RNA has a hydroxyl group (OH) attached there. RNA comes in all kinds: messenger RNA (mRNA) and transfer RNA (tRNA) being perhaps the most prominent.
tRNA can adopt 3-dimensional shapes not seen in DNA. This structure, the first tRNA structure determined, shows the typical shape of tRNA. It consists of two helix-like domains connected through a bulky bend, giving it the shape of the letter L. Calling the two arms of the L helical is somewhat of a simplification. The actual shape is more complex. At the top of the letter L sits what is the most important part of the tRNA molecule, the so-called anticodon loop. This is the site that is recognized on the ribosome and the bases there specify which kind of amino acid is connected to the tRNA. Scattered throughout the molecule are magnesium ions. DNA and RNA often have magnesium associated with them, as they are generally highly charged molecules due to the many oxygens of the backbone.
Protein Data Bank (PDB)
author: Arno Paehler