Hydrogen-bond patterns nucleotides

A Selection of Cyclic Hydrogen-Bonding Patterns Formed in Nucleoside and Nucleotide Crystal Structures... 

If the crystal structures and hydrogen-bonding patterns of uridine and thymidine and their simpler derivatives are compared with those of cytidine, it becomes obvious that the -NH2 functional group has a characteristic influence. The nucleosides without the -NH2 groups have less than average hydrated crystals, although the one nucleotide represented, uridine-3 -monophosphate, crystallizes as a monohydrate. 

Selected crystal structures of cytidlne and its derivatives. The cytidine-related nucleoside and nucleotide crystal structures for which reliable hydrogen-bond patterns can be reported include five nucleotides. Amongst the nucleotides there is more variety than with the uridine compounds. There are three hydrates, four hydrochlorides, and a nitrate. The conjugated NH2 group is always involved as a donor, but never as an acceptor. Several different configurations are observed ... 

For hemoglobin E the amino acid substitutions are lysine for glutamic acid. The codons for Lys are AAA and AAG while those for Glu are GAA and GAG. The difference is A - G in the first nucleotide of the triplet. Both of these bases are purines and would fit about the same in the helix of DNA. The hydrogen bonding patterns are different, with A involved in 2 while G is involved in 3, but hydrogen bonding to a lesser extent could still occur. 

Ribosomal RNA (rRNA) is involved in the protein synthesis. It is found in the ribosomes which occur in the cytoplasm. Ribosomes contain about 35% protein and 65% rRNA. Experimental evidence suggests that rRNA molecules have structures that consist of a single strand of nucleotides whose sequence varies considerably from species to species. The strand is folded and twisted to form a series of single stranded loops separated by sections of double helix, which is believed to be formed by hydrogen bonding between complementary base pairs. The general pattern of loops and helixes is very similar between species even though the sequences of nucleotides are different. However, little is known about the three dimensional structures of rRNA molecules and their interactions with the proteins found in the ribosome. 

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