Structure of Ribonucleic Acids

While the DNA function as the master copy of the genetic information, the RNA molecules are used as working copies for making proteins. Because of this function difference it may be concluded that DNA is more stable since it has to preserve its information content, whereas RNA appears to be constantly degraded and remade to synthesize proteins in changing circumstances.

Structurally, RNA differs from DNA in notable ways. Each molecule of RNA is single-stranded and is made as a complementary strand of one of the two chains of DNA. However, the RNA molecules are much smaller then molecules of DNA. Though it consists of a sugar-phosphate backbone, the sugar involved is ribose and an additional – OH group available at the C-2 position can have different linkage. Beside RNA molecules contain uracil as the base complementary to adenine. The molar ratios of purines and pyrimideines are also variable. Some viral RNAs are double of a double-helical nature which is stabilized through hydrogen bonds between bases and hydrophobic interactions.

Molecules of RNA are much smaller than those of DNA, sometimes as few as 120 nucleotide residues. This means that RNA represents a small fraction of the length of DNA molecule. The nucleotide residues are linked through 3’, 5’ phosphodiester linkages and the OH group at C-2 is free and is more susceptible to mid alkali hydrolysis.

RNA molecules don not occur as double helices with two separate chains, except in certain viruses where complementary chains like DNA are not formed. However, a molecule of RNA chain bends upon itself so as to bring portions of the chain in antiparallel alignment to generate a double helix owing to internal folding.

The RNA molecule is truly a functional molecule transcribed on DNA templates. There are three forms of RNA found in the cell, messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA), each of them having a different role in protein synthesis.

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