All enzymes are water soluble protein

Proteins or proteins are made up of amino acids. There are probably several hundred amino acids in nature, and they have even been found on comets or in meteorites. However, only proteinogenic amino acids are involved in the structure of proteins in the human body. Amino acids contain both the carboxy group COOH and the amino group NH2. The proteinogenic amino acids belong to the α-amino acids, since the amino group is located on the α-carbon atom, which is directly linked to the carboxy group. The simplest α-amino acid is glycine or aminoethanoic acid. After the three-letter code, glycine receives the code Gly.


The rest (marked green) can consist of different atom groups. In the case of alanine (2-aminopropanoic acid), for example, this radical consists of the alkyl group -CH3. There are two enantiomers of alanine, which are mirror images of each other. With the exception of glycine, the amino acids show mirror image isomerism. Cysteine ​​is an amino acid that contains a sulfur atom, in selenocysteine ​​this sulfur atom has been replaced by a selenium atom.

To date, 20 proteinogenic amino acids are known, which are coded in the human genome and recognized as amino acids for the construction of proteins. There are also other proteinogenic amino acids in the human body that are not genetically encoded, but are produced as a product of metabolic processes. As a rule, the proteinogenic amino acids are in the L-form. Essential amino acids must be ingested through food and cannot be produced by the body itself. Adults need eight essential amino acids. Children and pregnant women also need two more: cysteine ​​and tyrosine.

The amino group in one amino acid can react with the carboxy group of another amino acid, splitting water. The resulting C-N bond is called a peptide bond. In this way, molecular chains with many linked amino acids can be created. If the chain-like molecules contain fewer than 100 amino acid building blocks, it is Peptides. If the amino acids join together to form chains with many hundreds of building blocks, you get Proteins, the egg whites.

With 20 amino acids present, there is an enormous amount of possibilities to create various links. Life on earth uses these possibilities and constructs a multitude of protein structures with special tasks. To keep track of things, 20 amino acids have been given a three-letter code or a one-letter code. The sequence, i.e. the order of the link modules, is called Primary structure of a protein.

The peptide bond is around the carbon bonds around the α-Carbon atom rotatable, so the protein molecules arrange themselves spatially. One possibility would be the staircase-like folding sheet arrangement, another is that α-Helix in which the amino acid sequences are linked by hydrogen bonds in a spiral-shaped chain. There are 3.6 sequences per turn. This spatial arrangement caused by rotatability and intermolecular forces forms the Secondary structure of proteins. However, proteins can also form mixed arrangements. The relative arrangement of the secondary structures among each other is called Tertiary structure. There are protein molecules with several chains or those that form a large association with one another, this complex system describes the Quaternary structure.


The proteins can be divided into two groups: The fibrillar proteins or fiber proteins are wound into thick cables and strands. They can be found in hair, muscles, insect filaments, claws and skins. Wool and silk are also made up of fiber proteins. The molecular shape of the globular proteins is, however, more spherical. One example of this is hemoglobin, which is responsible for transporting oxygen in the blood. Fiber proteins tend to have supporting functions, globular proteins ensure that biochemical functions take place. The shape of the molecule determines the function of the protein. While the molecules of the proteins in a muscle tendon are spirally rolled up in a helix, which explains the elasticity of the tendon, hemoglobin molecules are spatially extended and leave enough space inside for the storage of oxygen.

Globular proteins are readily soluble in water, or they can absorb water well. One of them is albumin, which is found in the blood of the human organism as a control protein for osmotic pressure. Albumin is also found in abundance in milk and eggs. The egg white in the hen's egg can bind a lot of water. When whipping egg whites with a whisk, foam forms because air bubbles are trapped in the protein structures. At the same time, the protein is partially denatured and even more absorbent for water. In the Denaturation protein changes the secondary, tertiary and quaternary structure without affecting the primary structure. Denaturation can also take place through the action of heat, UV radiation, radioactive radiation or the action of substances such as water, acids, alkalis or alcohol.


Fiber proteins like keratin build hair and nails in humans. Fiber proteins are not soluble in water. Binding forces are active between the spirally wound fiber proteins in a hair, which creates cable strands, the microfibrils. Hundreds of microfibrils form an irregular bundle called macrofibrils. Several macrofibrils are combined to form a fiber strand. The sum of all fiber strands forms the hair shaft. The connective tissue of skin, flesh and bones is made up of the protein collagen. In the past, it was used to produce the binding agent bone glue. When boiled in water, the fiber protein swells up considerably when water is absorbed. After cooling, a protein-water gel forms in which the water molecules are trapped between the fiber strands. The gelatine formed in this way is a protein product that is obtained by boiling the rind and bones of slaughterhouse waste. Dried gelatine can absorb a lot of water and is used in numerous foods as a gelling agent for liquids. However, it is also used to manufacture drug capsules, as these dissolve easily in the stomach.

The proteins have a multitude of functions in the organism. Structural proteins like collagen make up at least 30 percent of the body protein in humans. They build up the skin, connective tissue and bones. The Enzymes belong to the globular proteins. They act as a biocatalyst to initiate metabolic processes. During digestion, the proteins are first broken down by the enzymes into peptides and then into amino acids, which are then taken up by the blood and transported to the cells. The amino acid sequences are used for the Protein biosynthesis needed, in which proteins are built with the help of DNA and ribosomes. Proteins are also of great importance as transport, regulation or control substances - for example in the case of hormones. Proteins can also be used to ward off diseases: the antibodies produced by white blood cells belong to the group of immunoglobulins.

Proteins are found in abundance in egg, milk, fish and meat products. But pulses such as peas, beans or soybeans and some seeds and nuts such as peanuts, pumpkin seeds or sunflower seeds are also rich in protein. Foods high in essential amino acids have high levels biological value. The reference value with the value 100 percent is the whole egg. The soybeans represent one of the highest quality protein-containing, plant-based foods. The biological value of the proteins in wheat flour is significantly lower, but in addition to the carbohydrates it contains glues consisting of gluten or glutinous protein. These significantly determine the baking properties of the flour. When baking bread, the glutinous protein holds water and the carbon dioxide formed by the yeast in small pores, which means that the dough “rises” and puffs up. This results in a fluffy pastry when baking. When baking, the water is released again, this pastes the starch into typical bread.
per 100 g
Protein contenttotalBiologicalValenceFat contenttotalcarbohydratesusable
Chicken egg 6 g100 %5.5 g0.3 g
Cow's milk3.3 g88 %3.8 g5 g
beef21 g92 %5 g0
tuna 21 g92 %15 g0
Soybeans35 g85 %18 g6 g
rice 7 g80 %2 g74 g
wheat flour 11 g50 %1 g71 g
Important, approximate base values ​​for proteins, values ​​in grams based on 100g of food

During putrefaction, putrefactive bacteria break down the proteins into ammonia and hydrogen sulfide. At the same time, other toxic breakdown products can also arise, which cause nausea and stomach upset in spoiled food. When an egg white is heated, ammonia and hydrogen sulfide can also be produced. The chemical detection of bound nitrogen and the detection of sulfur are based on this. Simple proteins and peptides are detected in the chemical laboratory using the biuret reaction, proteins with aromatic amino acid components such as phenylalanine are detected using the xanthoprotein reaction.

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