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Amino acids are organic compounds that contain amino and carboxyl groups, making them essential building blocks for biological organisms. They play a crucial role in cell structure and tissue repair. The body uses amino acids to create important proteins like antibodies, hemoglobin, enzymes, and hormones, which help regulate metabolism. Additionally, amino acids have unique functional groups and structures that make them valuable in various industries such as medicine, food, and cosmetics.
Amino acids have a basic structure consisting of a central carbon atom bonded to a hydrogen atom, an acidic carboxyl group (-COOH), an amino group (-NH2), and organic side chains (R groups). Proteins are made up of 20 different amino acids, each with the same central structure but varying R groups. The basic structure of amino acids is as follows:
Fig. 1. General structure of amino acids.
The properties of different R groups vary depending on the atoms present in the functional group. Some R groups are made up of mainly carbon and hydrogen, making them nonpolar or very hydrophobic. Others contain polar, uncharged functional groups like alcohols, amides, and sulfhydryl groups. Some amino acids are basic (with amine functional groups) or acidic (with carboxyl functional groups), allowing them to form complete charges and create ionic interactions. These properties impact how they interact with neighboring amino acids in peptides and proteins, ultimately influencing the three-dimensional structure and properties of the protein.
Each amino acid can be abbreviated with three-letter and one-letter codes. The table below shows the abbreviations and one-letter codes used for the 20 amino acids in proteins.
| Amino Acid | Three Letter Code | One Letter Code |
| Alanine | Ala | A |
| Arginine | Arg | R |
| Aspartic Acid | Asp | D |
| Asparagine | Asn | N |
| Cysteine | Gys | C |
| Glutamic Acid | Glu | E |
| Glutamine | Gln | Q |
| Glycine | Gly | G |
| Histidine | His | H |
| Isoleucine | Ile | I |
| Leucine | Leu | L |
| Lysine | Lys | K |
| Methionine | Met | M |
| Phenylalanine | Phe | F |
| Proline | Pro | P |
| Serine | Ser | S |
| Threonine | Thr | T |
| Tryptophan | Trp | W |
| Tyrosine | Tyr | Y |
| Valine | Val | V |
Amino acids are classified based on the presence of side chains, also known as R groups, which determine their properties and functions. They can be categorized into nonpolar, polar, and charged groups. Nonpolar amino acids have hydrophobic side chains that repel water, while polar amino acids have hydrophilic side chains that can bond with water molecules. Charged amino acids can be further divided into acidic and basic types, which are positively or negatively charged at normal pH levels. In terms of human nutrition, there are nine essential amino acids that must be obtained from the diet as the body cannot produce them. Non-essential amino acids can be synthesized by the body using other amino acids or metabolic intermediates.
| Classification | Amino Acids |
| Nonpolar (hydrophobic) amino acids | Glycine, valine, proline, isoleucine, leucine, methionine (methionine), and alanine. |
| Polar (neutral) amino acids | Cysteine, asparagine, threonine, glutamine and serine. |
| Acidic amino acids | Aspartic acid, glutamic acid. |
| Basic amino acids | Lysine, arginine and histidine. |
| Amino acids containing aromatic rings | Phenylalanine, tyrosine, tryptophan. |
| Essential amino acids | Valine, leucine, isoleucine, threonine, lysine, tryptophan, phenylalanine, methionine (methionine), histidine. |
The sources of industrial amino acid chemicals can be divided into two categories: natural and synthetic. In recent years, advances in biotechnology have made it possible to produce amino acids through genetically engineered microorganisms. By introducing genes encoding specific enzymes into bacterial or yeast cells, researchers can create strains of microorganisms that produce large amounts of the desired amino acids. This approach has revolutionized the industrial production of amino acids, allowing the development of new and improved products with enhanced properties and functionality.
Natural sources of amino acids include plant and animal proteins such as soy, corn, wheat, and fish. These proteins are rich in essential amino acids that the body cannot produce and must be obtained through diet. In the food industry, natural amino acids are extracted from plant and animal sources through processes such as hydrolysis, fermentation and enzymatic digestion. For example, soy protein hydrolysis produces amino acids such as glutamic acid, lysine, and arginine, which are used as flavor enhancers and nutritional supplements in processed foods. Another source of natural amino acids is microbial fermentation. Certain bacteria and yeasts are able to synthesize amino acids through the fermentation of sugars or other organic substrates. This process is widely used to produce amino acids such as glutamic acid, lysine, and threonine, which are used as feed additives in animal nutrition. Microbial fermentation offers several advantages over traditional extraction methods, including higher yields, faster production times, and lower production costs.
Unlike natural sources, synthetic amino acids are created in the laboratory through chemical reactions. The most common method for synthesizing amino acids is the Strecker synthesis, which involves the reaction of aldehydes or ketones with ammonia and hydrogen cyanide. This process leads to the formation of α-aminonitriles, which can be hydrolyzed to produce the corresponding amino acids. Synthetic amino acids have a wide range of industrial applications, including pharmaceuticals, cosmetics, and biotechnology. One of the main advantages of synthetic amino acids is their purity and consistency. Unlike natural sources, which may contain impurities or varying concentrations of amino acids, synthetic amino acids can be produced with high precision and control. This makes them ideal for use in pharmaceuticals and other high-value applications where product quality is critical.
Amino acids are crucial organic compounds that make up proteins and are essential for numerous physiological processes in the human body. They are necessary for synthesizing proteins, enzymes, hormones, neurotransmitters, and other vital molecules that are important for cellular and tissue function. In addition to their role in protein synthesis, amino acids also serve as precursors for other important molecules, provide energy, and help regulate metabolism. As a result, amino acids are widely utilized in medicine, nutrition, agriculture, and industry.
Monosodium glutamate is the first amino acid used by human beings, and it is also one of the condiments with the widest range of application in the world. Glycine, alanine, aspartic acid, leucine and asparagine have been found one after another to have flavoring effects, such as glycine for sweetness and leucine for bitterness. Lysine is one of the essential amino acids and the first limiting amino acid of protein, and is often used as a nutrition reinforcer. Adding lysine to rice, wheat, corn and other cereal foods can substantially increase the nutritional value of this type of protein. The sweet dipeptide synthesized by aspartic acid and phenylalanine is about 150 times sweeter than sucrose, and has the characteristics of pure sweetness, low caloric value, and superior absorption by human body, making its widely application in beverages, coffee, dairy products, etc. As calcium supplement products, calcium amino acid chelate and calcium aspartate have been commercialized.
In the pharmaceutical industry, amino acids are the raw materials for synthesizing human proteins, hormones, enzymes and antibodies, and are involved in regulating human metabolism and physiological activities. Amino acids and their derivatives can be used as nutritional agents, metabolic modifiers and special diets for special people. The special infusion for liver disease patients is made from a variety of branched-chain amino acids in a certain ratio; the special infusion for tumor patients is designed and prepared according to the special amino acid profile of tumor patients and together with therapeutic drugs. The amino acid infusion for infants and young children is prepared according to the characteristics that the kidney function is not fully developed and the liver and other tissues are weak in metabolizing nutrients. Amino acids are also used as excipients in pharmaceutical formulations to improve drug stability, solubility, and bioavailability.
In the cosmetics industry, amino acids are used in skin care products to moisturize, exfoliate, and repair the skin. The main amino acids used in cosmetics on the market are L-glutamic acid, L-proline, L-arginine, and L-serine. L-arginine is a precursor for the synthesis of nitric oxide, proline, creatine, etc. It plays a key role in cell proliferation, energy metabolism and endothelial function, and is considered a possible substitute for EGF as a repair component. Amino acid surfactant is a mild and degradable anionic surfactant. Its main active ingredient is the sodium salt of complex amino acids, which are mainly used in shampoos, baby toiletries, body washes and facial washes in daily chemical products. Amino acid surfactants are becoming more and more popular in the market because of their high safety, small usage, strong biological activity, good degradability and easy compounding.
Amino acids are also used in agriculture as fertilizers and animal feed additives. Amino acids are essential nutrients for plants and animals and play a vital role in growth, development and reproduction. In agriculture, amino acids are used as organic fertilizers to improve soil fertility and crop yields. Amino acids are also used as feed additives for livestock to improve growth performance, feed efficiency and overall health. In aquaculture, amino acids are used as feed supplements for fish and shrimp to promote growth and reduce mortality. Amino acids are also used in animal feed formulations to replace expensive protein sources such as soybean meal and fishmeal and to reduce the environmental impact of livestock production.
In biotechnology, amino acids are used to produce recombinant proteins, enzymes and antibodies. Recombinant proteins are proteins produced by genetically engineered microorganisms such as bacteria, yeast, or mammalian cells. Amino acids are used as raw materials for the synthesis of recombinant proteins, which are used in a variety of applications such as drug development, diagnostic testing, and bioprocessing. Amino acids are also used as substrates for the production of enzymes such as proteases, lipases and amylases, which are used in various industrial processes such as food processing, detergent manufacturing and biofuel production. Amino acids are also used as building blocks for the synthesis of antibodies, which are proteins used in immunotherapy, diagnostics, and research.
