Zoom in on microorganisms

DNA, RNA, proteins…what are they, anyway?

Agarose gelZoomZoom (109KB)
© Nicole Catellier, Cinémanima inc.
Genetic code tableZoomZoom (147KB)
© Armand-Frappier Museum

"DNA" is actually an abbreviation of the molecule's full name, deoxyribonucleic acid.

DNA is a molecule that is essential for all life on earth. All DNA, whether it comes from insects, plants, bacteria, or humans, has the same general structure. The fact that all organisms contain DNA is strong support for the theory that all life is derived from a common ancestor.

In some ways, DNA is like the assembly instructions for a living being. The components of DNA, known as genes, determine specific characteristics such the colour of our eyes, the length of our nose, and so on.

But while genes are the supervisors who give the orders, proteins are the workers who actually do the building. Proteins are complex molecules composed of many subunits known as amino acids. The characteristics of each protein are determined by the number and order of its amino acids, which in turn are determined by the instructions contained in the cell's DNA.

When we speak of DNA, the first image that comes to mind is that of two snakes, intertwined and connected to each other through a series of lines, or else that of a long chain of coloured beads. The snakes are in fact the two nucleotide chains that constitue DNA and the lines between them are true chemical bonds. The nucleotides are always made up of three parts, a sugar (S), a phosphate group (P) and a base (B). Nucleotides can only be differentiated from one another by their bases because the other two parts, the sugar and the phosphate group, are identical for all nucleotides. Four different bases exist, often associated with the letter A, T, C, and G.

To form a chain, the nucleotides bind to one another through the sugars and phosphate groups. Two chains can be linked together when the bases bind to one another. The A always links with the T and the C always links with the G. When the chains of nucleotides are finally long enough, the DNA begins to fold over onto itself and take on its characteristic snake-like appearance.

RNA, the bridge between DNA and proteins

RNA is the blueprint for protein production in all organisms, bridging the gap between DNA and proteins. As its name (ribonucleic acid) indicates, its structure is very similar to that of DNA – in fact, DNA acts as the model for RNA.

The first step in building a protein is the transformation of DNA into RNA, in much the same way that a book is translated from one language to another.

There are three structural differences between DNA and RNA, indicated in the following table:

Characteristic DNA RNA
Name of the sugar Deoxyribose
( the "D" in DNA)
Ribose
( the "R" in RNA)
Names of the four bases A (adenine) A (adenine)
T (thymine) U (uracil)
C (cytosine) C (cytosine)
G (guanine) G (guanine)
Number of chains 2 1