Amino acids are building blocks of life 氨基酸的来源

Amino Acids

building blocks of life

Why are amino acids important?

Amino acids (AA) are organic compounds that combine to form proteins. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen, although other elements are found in the side chains of certain AAs. Proteins and amino acids are the building blocks of life.

When proteins are digested or broken down, Amino Acids are left. The human body uses AAs to make proteins to help the body:

  • Break down food
  • Grow
  • Repair body tissue
  • Perform many other body functions

The primary functions of proteins are to build our muscles, bones, hair, and nails, but that is only the start. Amino acids make up the enzymes that facilitate the myriad chemical reactions in our bodies. They carry nutrients and other necessary molecules through our blood and across cell membranes. They carry signals from one part of the body to another. The antibodies which protect us from illness are also proteins. The tasks of proteins are just too many to count. AAs can also be used as a source of energy by the body.

What are the main types of amino acids?

There are totally 23 proteinogenic (protein building) amino acids, and over 100 natural amino acids, which are non-proteinogenic. Of the proteinogenic AAs, 9 are essential, 11 which are nonessential, and 3 of which are not found in the human body.

  Essential Amino Acids
  • Essential amino acids cannot be made by the body. As a result, they must come from food.
  • The 9 essentials are: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.
  • Out of the nine essential amino acids, three are the branched-chain amino acids (BCAAs): leucine, isoleucine and valine.
  • “Branched-chain” refers to the chemical structure of BCAAs, which are found in protein-rich foods such as eggs, meat and dairy products. BCAA supplements have been shown to build muscle, decrease muscle fatigue and alleviate muscle soreness.
  • Studies report that total BCAA intakes between 15–35 grams per day seem generally safe
  Nonessential Amino Acids
  • Nonessential means that our bodies produce an amino acid, even if we do not get it from the food we eat.
  • They include: alanine, arginine, asparagine, aspartate, cysteine, glutamine, glycine, ornithine, proline, serine and tyrosine
  • Out of the 11 non essentials, 8 of them are so called “conditional”, i.e., are usually not essential, except in times of illness and stress. They are: arginine, cysteine, glutamine, tyrosine, glycine, ornithine, proline, and serine.
  • A naturally-occurring chemical compound, carnitine or L-carnitine, is technically speaking, not an amino acid. It is actually a dipeptide made from the essential amino acids lysine and methionine. It is therefore often classed as a conditionally essential AA.

Sources of Amino Acids

Animal-based foods such as meat, milk, fish, and eggs provide essential AAs. Plant-based foods such as soy, beans, nuts, and grains also contain essential amino acids. Animal foods are the highest quality protein sources. Plant sources lack one or more amino acids, which makes it more difficult to get all the AAs that your body needs.

Whey protein is one of the few sources that naturally contain all 20 amino acids, making it a complete protein.

It isn’t necessary to eat essential amino acids at every meal. You can get healthy amounts by eating foods containing them throughout the day. For certain age group and particular athletes, as well as people with certain health conditions,  supplementation with amino acids are necessary. Ask your doctor for advice.

Amino acids  are available as individual AAs or in AA combinations. They also come as part of multi-vitamins, proteins, and food supplements. Usually, you should take AA combinations instead of individuals.  Using a single amino acid supplement may lead to negative nitrogen balance. This can decrease how efficient your metabolism is. It can also make your kidneys work harder. 

To further learn about proteins for academic purpose, you can visit the Protein Database of NCBI (National Center for Biotechnology Center).

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Studies have shown that high-protein foods help people feel fuller, longer, as opposed to foods heavy in carbohydrate or fat content, ultimately reducing overeating.  A majority of Carnitine, a non-essential amino acid, is found in the muscles. Carnitine has been shown to supply oxygen to muscles, which can aid in exercise recovery. 

One of glutamine’s benefit is improving gut health, but glutamine can also be converted to glucose without affecting the body’s glucagon and insulin counts.  This enhances the energy supply while passing up fat storage caused by insulin. Essentially, Glutamine protects your body from storing sugars and fats, allowing you to feel more energized and alert.  

N-acetyl cysteine (NAC) is a supplement form of cysteine.

Consuming adequate cysteine and NAC is important for a variety of health reasons — including replenishing the most powerful antioxidant in your body, glutathione. These amino acids also help with chronic respiratory conditions, fertility and brain health.

Essential Amino Acids

Histidine supports brain health and neurotransmitters. It also helps to detoxify the body by producing red and white blood cells, which are needed for overall health and immunity. Histidine can even help protect tissues from damage caused by radiation or heavy metals.

Sources of Histidine: red meat, diary products,  white meat and poultry, seafood, soybeans, beans, etc

Isoleucine is an isolated form of leucine that helps the body produce haemoglobin. Haemoglobin carries iron in the blood and regulates blood sugar which is burned for energy in the muscles during exercise. Whey protein isolate is naturally high in Isoleucine. Isoleucine also assists nitrogen growth within the muscle cells, which is a large part of our structural and DNA makeup.

Sources of Isoleucine: soy, meat and seafood, dairy products, rice, etc

Leucine helps to stimulate muscle strength and growth, and helps to retain lean muscle when dieting. Leucine is the main amino acid directly responsible for activating an essential compound in muscle called mTOR, which is directly responsible for up-regulating protein synthesis. Leucine provides the basic building blocks for muscle and helps to synthesis more. Leucine also helps to regulate blood sugar levels by moderating insulin into the body during and after exercise, and has a positive impact on our brain and neurotransmitters.

Sources of Leucine: diary, soybeans, meat, nuts, seafood, etc

Lysine is one of the main amino acids that is responsible for muscle repair and growth, and has also been shown to boost the body’s immune system. Lysine also helps the absorption of other minerals in the body and is needed for the synthesis of collagen which is the main element needed for the formation of connective tissue and bones in the body.

Sources of Lysine: eggs, meat, poultry, beans, peas, nuts, whey protein.

Methionine is important for the growth of new blood vessels and muscle growth, and it contains sulphur, which is integral to tissue and muscle health. Without enough sulphur in the body, people can be susceptible to arthritis, damaged tissue, and have trouble healing. Methionine also aids in the production of muscle growth and the formation of creatine, which is needed for energy. Methionine can also dissolve fat within the body and reduces fat deposits in the liver.

Sources of Methionine: meat, fish, dairy, beans, rice, etc

Phenylalanine is turned into the amino acid tyrosine within the body, which is needed to make proteins and brain chemicals such as epinephrine, L-dopa, norepinephrine, and thyroid hormones. Phenylalanine therefore has a large impact on our mood and mental health.

Sources of Phenylalanine: dairy, meat, fish, chicken, eggs,  beans, rice, etc

Threonine supports health function of the immune system, liver, heart, and the central nervous system. It is also needed to create glycine and serine, amino acids that are necessary to produce elastin, collagen, and muscle tissue. It is essential for the healthy working of the muscles, and help to keep them strong and elastic. Threonine also helps to build strong bones, and can help to accelerate the healing of wounds and tissue injuries.

Sources of threonine: lean meat, cheese, nuts, leafy greens,  soybeans, etc

When tryptophan is absorbed by the body, it is eventually turned into serotonin – the chemical responsible for making us feel happy, is a neurotransmitter, and helps to lower stress levels and depression. Tryptophan is also known for inducing a relaxing effect on the body, and promotes healthy sleep patterns, as well as supporting brain function and nervous system function.

Sources of tryptophan: chocolate, diary, red and white meat, eggs, fish, nuts, etc

Valine is essential for optimal muscle growth and repair. It helps to supply the muscles with extra glucose responsible for energy production during physical activity, making it essential for endurance and overall muscle health. It also helps to smooth working of the nervous system and cognitive function, as well as curing metabolic and liver diseases.

Sources of valine include: cheese, red meat, nuts, beans, spinach, legumes, whole grains, etc.

Non essential Amino Acids

Alanine is produced by other amino acids like pyruvate and leucine, valine and isoleucine. It is popularly known as L-Alanine. A more dense form exits by the name of Beta Alanine. Beta Alanine has applications in the sports industry as it is a performance improver.

Arginine is an amino acid and plays an important role in cell division, wound healing, removing ammonia from the body, immune function, and the release of hormones. It is a precursor for the synthesis of nitric oxide (NO), making it important in the regulation of blood pressure.

Asparagine is known as the first amino acid to be isolated from its source. Asparagine plays a major role in synthesis of glycoproteins. In the human body, it is synthesized by the liver.

Aspartate is commonly known as Aspartic Acid and it is a negatively charged polar amino acid. It is synthesized by the liver in the human body. Aspartate exists in combination of chemical substances as well.

Cysteine is widely used by the human body for various important functions. In supplements, it is usually in the form of N-acetyl-L-cysteine (NAC).The body converts it into cysteine and then into glutathione which is a powerful antioxidant.

Glutamine is an important amino acid with many functions in the body. It is a building block of protein and critical part of the immune system. What’s more, glutamine has a special role in intestinal health. 

Glycine is an “essential amino acid” because the body can make it from other chemicals. The primary sources are protein-rich foods including meat, fish, dairy, and legumes. Glycine is used for treating schizophrenia, stroke, benign prostatic hyperplasia (BPH), and some rare inherited metabolic disorders.

L-ornithine is an amino acid that is primarily used in the urea cycle, which eliminates excess nitrogen from the body.

Proline is a proteinogenic amino acid that is used in the biosynthesis of proteins. Proline plays important roles in molecular recognition, particularly in intracellular signalling.

Serine is also known as L-serine. It is synthesized by the body from glycine and threonine, which themselves are amino acids. Serine offers a number of physical and mental health benefits.

Tyrosine, or L-tyrosine, is an amino acid that the body produces from phenylalanine. Supplementing with it is thought to increase important brain chemicals (neurotransmitters), which affect your mood and stress response. 

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