As building blocks for proteins, amino acids are indispensable for the human body and other living organisms. This is because proteins serve as important substances for the construction of cellular and extracellular structures.
Among the numerous amino acids, there are 20 acids that have a proteinogenic effect in humans. Eight of these protein building blocks cannot be produced by the human organism itself, so they must be taken in regularly with food. They are therefore also called indispensable or essential amino acids.
Why proteins are so important for the body
In the cells of all living organisms, macromolecular substances occur which, due to their properties and chemical structure, are similar to the protein in bird eggs. Therefore they are called proteins.
The foreign word “protein” is derived from the Greek word “proteios” for “the first” or “the most important”. This already gives us an indication of the importance of proteins for living organisms.
Comparable to carbohydrates, proteins perform a large number of important tasks within the body. However, proteins have a macromolecular structure and their building blocks are amino acids.
The most important tasks of proteins are
- enzymatic catalysis,
- transport and storage,
- the coordinated motion,
- mechanical support functions,
- the strengthening of the immune system,
- the triggering and transmission of nerve impulses,
- growth control and cell differentiation.
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Enzymatic catalysis
Nearly all chemical reactions in the body are carried out by certain macromolecules, which we call enzymes and which consist mainly of proteins. This is why we also speak of enzymatic catalysis.
Some of these processes are simple, while others – such as the duplication of a DNA strand – are very complicated. In the living organism, there are very few chemical processes that take place without enzymes. Therefore, they are of particular importance.
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Transport and storage
A special group of proteins is responsible for the transport of small molecules and ions. For example, the well-known haemoglobin serves as an oxygen carrier in the red blood cells (erythrocytes). The related protein myoglobin performs this task in the muscles.
Iron, in turn, is moved in the blood plasma by transferrin and stored in the liver together with ferritin in a complex.
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Coordinated movement
Proteins form the essential component of muscle tissue. Its contractions are carried out by two different types of filaments, which also consist of proteins. Even microscopically small movements such as the locomotion of sperm cells or chromosome migration during cell division (mitosis) are based on proteins.
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Mechanical support functions
Human bones and skin have high tensile strength. This is guaranteed by the well-known collagen, which is also a (fibre) protein.
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Strengthening of the immune system
A highly specific group of proteins is represented by antibodies in the organism.
They are able to recognise, bind and render harmless viruses, bacteria and foreign cells of other organisms.
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Triggering and transmission of nerve impulses
When certain stimuli – cold, heat, pain and others – are applied to the nerve cells, they respond with the help of so-called receptor proteins.
One example is rhodopsin in the rods of the retina in the eye, which serves as a photoreceptor. Other receptor proteins can be stimulated by molecules such as acetylcholine. They regulate the transmission of nerve impulses at the connections (synapses) between the nerve cells.
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Growth control and cell differentiation
We also need proteins in our body for the differentiation of the various body cells and their proper growth based on the genetic information available. We, therefore, call them “growth factor proteins”.
The formation of neural networks, for example, is controlled by a “nerve growth factor”. Other cell activities are coordinated by hormones. The majority of all these substances are proteins, including insulin, for example.
In general, we understand proteins in the cells as sensors that direct the flow of energy and matter.
The complex interaction of the proteins
The task list of proteins is not complete. This is partly due to the fact that the interaction of the individual proteins is very complex. Scientists have so far only been able to describe it in hints.
The technical term for the totality of all proteins and their interaction in the organism is “proteome”. Comparable to the term “genome” for all genes in the body.
Since the vital proteins are generated from at least one amino acid, we can draw appropriate conclusions about the supply of the small protein building blocks.
In a nutshell, it can be said: Without amino acids, there is no protein, and without protein, there is no proper control and monitoring of vital body or metabolic functions.
Why a sufficient supply of amino acids is important
Before we go into the above-mentioned tasks in detail, a few remarks on the interaction of amino acids and proteins.
Since proteins are vital and are formed from amino acids, it is obvious how important the latter are.
As soon as even one amino acid is not present in the body, all proteins are impaired in their functions. A permanent deficiency can, therefore, have harmful consequences for health.
The most common consequences of amino acid deficiency include increased susceptibility to
- infections,
- joint problems,
- deficits in the development of the muscles and
- a general drop in performance and concentration.
Some diseases of civilisation such as diabetes or overweight can also be traced back to a metabolic disorder and thus to a lack of amino acids.
In order to determine this, physicians can carry out an analysis of your amino acid content to determine the given concentration in your organism.
Conversely, it should be noted that – similar to vitamins – an oversupply of the small protein building blocks could also be harmful to health.
Anyone who takes amino acids via dietary supplements should therefore always check the correct dosage. For example, a too high concentration over a long period of time can have a negative effect on the kidneys or liver.
Aromatic amino acids
We call amino acids aromatic if they have a corresponding side chain in their chemical structure. Here we discuss their properties and occurrences.
The four aromatic protein building blocks are:
- Phenylalanine
- Tyrosine
- Tryptophan
- Histidine (whereby this is also partly assigned to the protein building blocks with a basic side chain)
The first three aromatic representatives in this list have in their chemical structure a benzene ring in the side chain. An exception is histidine, which here has an imidazole ring.
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Phenylalanine
Phenylalanine is an essential amino acid and a precursor of tyrosine, from which in turn hormones and other important substances such as adrenaline are formed. Especially infants need a high daily intake in the first months of life.
With increasing age, the requirement decreases significantly.
The aromatic phenylalanine is found especially in the following foods:
- dried soybeans
- dried peas
- pumpkin seeds
- walnuts
- poultry
- pork
- salmon
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Tyrosine
Since tyrosine is formed from phenylalanine, this amino acid is also considered aromatic, it though belongs to the non-essential protein building blocks. However, it becomes essential as soon as there is a deficiency of phenylalanine.
This is the case with the disease phenylketonuria. This is a metabolic disease due to an enzyme deficiency in which phenylalanine cannot be broken down. This causes it to accumulate in the body.
Therefore, on the one hand, neurological consequential damages occur. On the other hand, the organism cannot produce tyrosine or the substances synthesized from it. As a consequence, it is necessary to abstain from foods containing phenylalanine and at the same time take in tyrosine.
Tyrosine is responsible for the production of adrenaline and noradrenaline, which increase the heart rate and blood pressure. In addition, this aromatic amino acid is the starting material for certain thyroid hormones that influence the metabolism and basal metabolic rate.
The neurotransmitters dopamine and L-dopa also arise from tyrosine. They are responsible for
- signal transmissions in the brain,
- for memory and concentration and
- the motion control.
If the body does not have sufficient tyrosine at its disposal, not only will the above-mentioned substances be reduced. Also, the substance melanin, which is needed for the pigmentation of skin, eyes and hair, can then no longer be produced sufficiently.
In addition, tyrosine as an aromatic protein building block is a structural component of insulin receptors and therefore crucial for insulin signal transmission.
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Tryptophan
The aromatic tryptophan is an essential amino acid and a precursor of niacin, which is very important for our energy metabolism. Furthermore, tryptophane is regarded as a basic product for the hormones melatonin and serotonin. The latter is also known as the happiness hormone.
A lack of this could lead to depression and a reduced sense of pain. Conversely, an excessive amount of pain can cause restlessness, anxiety and depression.
Serotonin is also beneficial for blood clotting and has a slight appetite suppressant effect. Together with melatonin, it regulates the human sleep-wake state.
Melatonin, in turn, is generated directly from serotonin. The hormone supports falling asleep and is responsible for a restful sleep. During the deep sleep phase, it reaches its peak in the bloodstream.
Tryptophane, which is important for all the substances mentioned above, can be found mainly in the following food sources:
- soybeans
- dried peas
- cashew nuts
- cocoa
- pork
- poultry
- salmon
Similar to phenylalanine, infants, in particular, are dependent on a high daily intake compared to adults.
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Histidine
Histidine is one of the essential amino acids and, like phenylalanine and tryptophan, is also required to a greater extent by infants and small children.
The protein building block can be found for example in:
- dried soybeans
- dried peas
- wheat germ
- beef
- tuna
- salmon
Histidine is essential for the formation of histamine, a hormone-like substance that is responsible for numerous functions in the human body. These include the muscle contractions of the bronchi and uterus.
Histamine has a dilating effect on the blood vessels, promotes the secretion of gastric juice and stimulates intestinal peristalsis. Increased histamine production is seen in allergic reactions, strong sunlight or burns.
In such cases, the substance increases blood circulation, which is visually expressed as reddening of the skin.