Fundamentals of Molecular Biology - V.I. Rezyapkin 2009

Nucleic Acids
Spatial Organization of RNA

Natural RNAs can be divided into two groups: single-stranded and double-stranded RNAs. Double-stranded RNAs consist of two mutually complementary RNA strands. This type of RNA is found in certain Viruses. In terms of their Organization, double-stranded RNAs are similar to DNA. They are wound into a right-handed double helix, their RNA strands are antiparallel, Hydrogen Bonds are formed between complementary bases, and the sugar-phosphate backbone is located on the outside of the helix.

Most natural RNAs are single-stranded. Despite this, their Structure may contain double-helical regions alternating with linear single-stranded RNA segments. The double-helical fragments are formed by complementary RNA regions located within a single strand (Fig. 1.8). In some cases, the proportion of double-helical regions in RNA can reach 75 - 90 %.

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Fig. 1.8. Double-stranded hairpins in an RNA molecule

Unpaired nitrogenous bases occur within the RNA double helix, and GU pairs may also be present alongside Watson-Crick pairs (AU and GC).



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