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Structure of RNA

Table of Contents

  1. The Components of RNA and a few principles
  2. RNA: a few facts
  3. What's in a name
  4. To go further

The Components

RiboNucleic Acids consist of:
  1. Riboseask Dr Chromo! (a pentose = sugar with 5 carbons)
  2. Phosphoricask Dr Chromo! Acid
  3. Organic (nitrogenous) bases: Purinesask Dr Chromo! (Adenineask Dr Chromo! and Guanineask Dr Chromo!) and Pyrimidinesask Dr Chromo! (Cytosineask Dr Chromo! and Uracilask Dr Chromo!)

An RNA molecule is a linear polymer in which the monomers (nucleotides) are linked together by means of phosphodiester bridges, or bonds. These bonds link the 3' carbon in the ribose of one nucleotide to the 5' carbon in the ribose of the adjacent nucleotide.

This is illustrated in Figure 1.

Organic BaseOrganic BaseOrganic BasepurineriboseRiboseRibosepyrimidineacid phosphoric acid phosphoric  acid phosphoric

Figure 1: A segment of a single nucleic acid chain. This is a clickable map.

Figure 2: model of a molecule of RNA. It is not a double helix, but in some places, (shaded in green), the positions of the bases are stabilised by hydrogen bonds.

Naming nucleosides and nucleotides.

Definitions Bases
  Adenine (A) Guanine (G) Cytosine (C) Uracyl (U)
The combination of a ribose and a base constitutes a nucleoside . Adenosine Guanosine Cytidine Uridine
The combination of a phosphate, a ribose and a base constitutes a nucleotide. Adenylate Guanylate Cytidylate Uridylate

RNA : a few facts...

RNA is found in the nucleus, where it is synthesised, and in the cytoplasmask Dr Chromo!, as messenger RNA, transfer RNA or ribosomal RNA. All these forms of RNA are involved in the protein synthesis.


Most RNA in the cell is single stranded and does not form a double helix.

Although each RNA molecule has only a single polynucleotide chain, it is not a smooth linear structure. It has extensive regions of complementary AU, or GC pairs. Therefore, the molecule folds on itself forming structures called hairpin loops. In the base paired region, the RNA molecule adopts a helical structure as in DNA.

What's in a Name

R Ribo: the pentose has an oxygen in position 2. Compare riboseask Dr Chromo! and deoxyriboseask Dr Chromo!.
N Nucleic: these molecules were first found in the nucleus of the cell, before being found in mitochondriaask Dr Chromo!, the chloroplasts of plants, and in the cytoplasm of prokaryotes
A Acid: only two of the three acid groups of the phosphoricask Dr Chromo! acid are used to form the DNA chain. The third one gives the phosphoribo-backbone an acidic property.

There is more than one RNA...

There are three major classes of RNA
  1. messengerRNA or m RNA: carries the genetic information out of the nucleus for protein synthesis.
  2. transferRNA or t RNA: decodes the information.
  3. ribosomalRNA or r RNA: constitutes 50% of a ribosome, which is a molecular assembly involved in protein synthesis.

And to go further

A little bit more work

  • Do you think this page looks like the page about DNA? Compare them, and find out the differences.

Belorussian translation

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