All about protein

In the following article we want to tell you a little more about proteins. Of our three macronutrients (carbohydrates, proteins, fat), proteins represent the most diverse group of molecules. They play a role in virtually all biological structures and processes in our bodies.

When it comes to nutrition, we often just talk about how proteins are important for muscle maintenance and should be included in our diet in a certain ratio. In this context, proteins are readily generalized to a uniform substance. Of course, there is no one protein, but thousands of different proteins in different sizes, shapes and most importantly: with different tasks.

The smallest structural unit of proteins is called amino acids. There are 20 proteinogenic – that is, protein-forming amino acids. All proteins are composed of these 20 amino acids. Like the Lego bricks in a Lego box, amino acids can also be put together in countless combinations. Each combination provides a different protein. Some proteins consist of only a few hundred amino acids, others of several thousand.

Amino acids are very small molecules that differ in their structure and properties. However, it is crucial for the classification as an amino acid that all amino acids have both a so-called “amino group” and a “carboxyl group”. These are specific groups of atoms in the molecule that have a significant influence on the properties of the molecule as a whole. Such special groups of atoms are also called “functional groups”. In proteins, it is precisely these two groups of molecules that form the links between the individual amino acids. This bond is called a peptide bond. In this way, the individual amino acids link up to form long chains. Imagine a train with many wagons. Each amino acid is a wagon and has a coupling at the front and back. On one side the wagon has a hook, on the other – an eyelet. The hook from one wagon always fits into the eyelet of a second wagon. Hook and eye are the amino and carboxyl groups. You can only ever connect hook (amino group) and eye (carboxyl group) together, never hook & hook or eye and eye. Thus, the amino acid wagons always look in the same direction, but theoretically, infinitely long connections are possible. By the way, there is an infinite number of each amino acid – for example, a protein can also contain the same amino acid 20 times. Thus, very long combinations are possible.

Even though you cannot see such a single protein molecule, it is important to realize that proteins have a spatial structure. They take up space in the room and they have a very specific shape that is unique to each protein.

The long chain of amino acids strung together is the so-called primary structure of proteins. Each protein has a unique sequence of amino acids that is characteristic of that protein. In addition to this primary structure, however, a protein continues to fold into a very specific shape.

Photo1: Shutterstock / molekuul_be
Photo 2: Shutterstock / magnetix

In simplified terms, this can be explained as amino acids preferring to interact with amino acids that are similar to them. However, if these amino acids are not directly next to each other, the bead chain must fold so that these amino acids come closer together. A protein can be composed of helices only or of leaflets, or it can have both helices and leaflet structures. The overall 3-dimensional appearance of the protein is called the tertiary structure. For example, there are more spherical proteins, such as hemoglobin, or long fibrous proteins, such as collagen.

Let’s summarize again: Each protein has a specific sequence of amino acids and takes on a characteristic shape. Both are quite crucial for their biological function. But what happens now if I change this structure?

It works very similarly for yogurt. Only here, acid is used and not heat. The lactic acid bacteria eat the lactose contained in the milk and produce lactic acid. The acid causes the caseins (certain milk proteins) in the milk to lose their solubility and precipitate. They then accumulate together, forming a 3-dimensional protein network that ensures that the yogurt becomes firm.

In the case of cheese, by the way, the whole process takes place enzymatically. The rennet (an enzyme necessary for cheese production) cuts off the water-soluble amino acid groups from the casein surface, so to speak. This also causes the casein to become insoluble and solid cheese to form.

I have already mentioned one or the other protein in the previous text. Many proteins today are also used with the English name, such as the Whey. Therefore, here is a brief overview of the origin and designation of the most important dietary proteins:

Different proteins are found in both the egg yolk and the egg white. Egg yolk additionally contains fat. The most abundant protein in terms of quantity is ovalbumin, which is found in egg white.

In addition to muscle proteins, such as myosin and actin, to name two important representatives, there are also connective tissue proteins, such as collagen and elastin. Collagen plays a more important role in our diet. It is found mainly in hides, tendons, bones, and connective tissue-containing meats.

Plants are also becoming increasingly important as a source of protein. Plant sources of protein include hemp seeds, rice, peas and lupine.

In the other articles of our protein series, we will highlight, among other things, the importance of proteins in food production and the different value of proteins from animal and plant sources.