Basic Biology - Molecules of life - Proteins

A protein may be formed from more than one chain of amino acids

In which case it is said to have quaternary structure. For example haemoglobin, is made up of four chains each of which is capable of binding an iron molecule.

Proteins are much too small to be seen in an optical microscope - a characteristic protein size varies from about 3 to 10 nanometers (nm), i.e., 3 to 10 times 10^-9 m. Solving (i.e., discovering) their structure is a difficult and expensive exercise, approximately €50,000 - €200,000 per novel structure. This is done by a variety of methods including X-ray crystallography, nuclar-magnetic resonance spectroscopy, and advanced electron microscopy.

PDBe is a database of known protein structures, which is housed and developed at the EBI. The image above shows the structure of triosephosphate isomerase visualised by RasMol software package, a 3D viewer for PDBe structures.

The size of this protein in a crystallised state is about 13 x 7 x 5 nm. The image above is only a model of these molecules, as the molecules are two small to have a ‘real’ image. For instance they cannot have any conventional colour, they are in constant motion, and when we start zooming in into a finer structure, quantum effects, such as Heisenberg uncertainty principle start playing a role.