From Amino Acid to Protein: The Structure of Proteins

Skin, hair, egg white, spider webs, gelatine and silk. These are all substances with totally different properties, but they have one thing in common: They consist of proteins, and thus they are all made of the same basic building blocks.

What Are These Building Blocks of Proteins?

The smallest units all proteins are composed of, are called amino acids. These are compounds that possess an acid group (COOH) and an alkaline amino group (-NH₂), as you can see in the picture. The 'R' stands for the remaining molecule, which can be composed in different ways. That is were the respective amino acids differ from each other.

In proteins, 20 different amino acids occur. The body is able to build most of them by itself, except for eight. These are called essential amino acids, and they have to be taken along with the food entirely. Essential amino acids are mainly found in animal protein.

How Do the Amino Acids Form a Protein?

Single amino acids can assemble into chains by linking their acid group to the amino group of a different amino acid. A protein is such a chain that consists of at least 100 amino acids, sometimes even more than thousand. So proteins are giant molecules.

How Are the Different Structures And Properties Generated?

First, every protein is characterised by the sequence of the different amino acids in the chain. This is the primary structure.

The chains can assume different spatial orientations or secondary structures: In the keratin of the hair, for example, the chains are spiral, which makes the hair elastic and stretchable. In silk, on the other hand, many parallel chains are assembled side by side into a plane structure. As a result, the silk thread is hardly stretchable, but smooth and robust.

The tertiary structure, that is the final three-dimensional form of the protein, is responsible for the biological function and the effectiveness of the protein.

How Stable Are Proteins?

As soon as the spatial structure of a protein is changed, its initial function is lost. The protein becomes denatured. This can be brought about by several influences, to which the proteins are very sensitive:

• Heating: When cooking eggs, for example, the protein is denatured, and the egg becomes solid.
• Mechanical load: When whipping egg white, the protein is denatured as well.
• Change of the pH value: When milk turns, you can observe that the contained protein flocculates.
• That is the reason why foods containing protein can be preserved with salt or alcohol.