Essential amino acid
An amino acid that an organism needs but cannot produce itself is called an amino acid that is essential for it .
Autotrophic organisms like plants are usually able to produce all the amino acids they need. Heterotrophic organisms, on the other hand, often need several specific amino acids as part of their diet in order to survive in the long term; an organism in different stages of development can have different requirements.
In humans
Isoleucine , leucine , lysine , methionine , phenylalanine , threonine , tryptophan and valine are essential amino acids for humans . Arginine and histidine only need to be ingested with food in certain situations such as growing up or recovery and are therefore referred to as semi-essential .
| amino acid | Amount of food in mg per kg of body weight per day |
|---|---|
| Histidine | 10 |
| Isoleucine | 20th |
| Leucine | 39 |
| Lysine | 30th |
| Methionine + cysteine | 15th |
| Phenylalanine + tyrosine | 25th |
| Threonine | 15th |
| Tryptophan | 4th |
| Valine | 26th |
In metabolic diseases, other amino acids also become essential: For example, in the presence of phenylketonuria (PKU), the normal conversion of phenylalanine into tyrosine does not take place. In this case, tyrosine becomes an essential amino acid. In such cases one speaks of conditionally essential amino acids. Other examples are arginine , cysteine and glycine .
The distinction between essential and non-essential amino acids is still fuzzy, as the human body can convert some amino acids into others: The sulfur-containing amino acids methionine and homocysteine can be converted into one another, but humans cannot produce either; furthermore, cysteine can be produced from homocysteine. The sulfur-containing amino acids thus form their own subgroup within the human metabolism. Another subgroup are arginine , ornithine and citrulline , which can be converted into one another by means of the urea cycle .
Amino acids in food
Foods that are deficient in essential amino acids generally provide the organism with insufficient amino acids. The organism needs a balanced mixture of amino acids; If an amino acid is too low, the other amino acids are not used to build up protein, but are broken down into fats and sugars ( deamination ). The Protein Digestibility Corrected Amino Acid Score , the amino acid index or the biological value measure the quality of the amino acid ratios . There is evidence that the brain recognizes a lack of essential amino acids in food.
vegetarianism
All essential amino acids are found in plants; therefore, a suitable combination of vegetarian or vegan products can provide people with sufficient amino acids. With regard to the amino acid supply , the quality of the vegetarian diet of humans can be increased by suitable combinations (such as legumes and cereal products ). A sufficient supply of all essential amino acids can only be achieved with a complex, sufficiently caloric combination of plant-based foods.
Medicine and sports
The amino acids valine , leucine and isoleucine are referred to as branched-chain amino acids (abbreviated BCAA for English B ranched- C hain A mino A cids ). They occur in all protein-containing foods and are used in intensive care medicine and geriatrics . In weight training and endurance sports they are used as dietary supplements used.
See also
Notes and individual references
- ↑ The sentence: "Unfortunately, important molecules are missing in the body of many animals" can serve as a memory aid for the eight essential amino acids mentioned, in which the first letters LFWMIKVT of the words represent the one - letter codes of the amino acids Leu (L) Phe (F) Trp (W) Met ( M) Ile (I) Lys (K) Val (V) Thr (T) .
- ↑ Protein and amino acid requirements in human nutrition, Report of a Joint WHO / FAO / UNU Expert Consultation (PDF; 4.2 MB), p. 150.
- ↑ Deficit warning in the brain. In: Wissenschaft.de. March 18, 2005, accessed on September 8, 2019 (“[How] rodents notice an amino acid deficiency within 20 minutes and can thus adjust their food intake accordingly.”).
- ↑ J. McDougall Plant foods have a complete amino acid composition. In: Circulation . 2002; 105 (25): e197.
- ↑ Diet: Vegetarian is not healthy per se. In: Pharmaceutical newspaper. Avoxa Media Group Deutscher Apotheker GmbH, accessed on May 6, 2020 .
- ↑ a b Hilmar Buchardi ea (Ed.): Die Intensivmedizin . 9th edition. Springer , Berlin / Heidelberg 2004, ISBN 3-540-00882-9 , pp. 240 ( limited preview in the Google book search - "No other group of amino acids has received so much attention in recent years as the branched-chain amino acids valine, leucine and isoleucine.").
- ↑ Hans-Konrad Biesalski ea (Ed.): Nutritional medicine . 3. Edition. Thieme , Stuttgart 2004, ISBN 3-13-100293-X , p. 234–235 ( limited preview in Google Book search).