What Are Amino Acids?

Lucy Bell-Young

by Lucy Bell-Young

10th November 2021

Amino acids are organic or carbon-based compounds that have two functional groups: an amino group and a carboxylate group. 

The amino group is slightly basic, while the carboxylate group is acidic. See the illustration below for an example. The R group or side chain mainly determines the amino acid’s chemical and physical properties. It can be of various sizes, shapes, and reactivities.

Diagram of amino acid structure

Amino acids are referred to as the ‘building blocks’ of protein (and of life), because proteins are formed from them. This is why amino acids are most commonly found in living organisms, though they can also be found in meteors and comets

Inside the cell, the instruction for specific chains of amino acids is provided by the genetic material, either DNA or RNA. Proteins can be composed of just a few hundreds of polymerised amino acids, or thousands of them in polypeptide chains. The sequence and the three-dimensional folding of the polypeptide chain determine the properties of a protein.

What Are Amino Acids Used For?

Amino acids link together to form long polypeptide chains, which form proteins. Therefore, they are considered the building blocks and molecular backbone of proteins. The sequential chains of amino acids are the primary structure of proteins

There are also secondary and tertiary protein structures. See the illustration below for the different structures of proteins:

Diagram of protein structure

Amino acids are present in many food products and some drinks, e.g. milk. All living organisms have them in their systems, either in free form or as part of protein structures and other biological molecules, such as enzymes. When we eat food, the proteins in those foods are broken down into amino acids through digestion.

While the human body can also synthesise some amino acids, many of the ones we need are from our diet. These are the ones that we cannot biologically manufacture. They’re called essential amino acids, and are solely derived from what we eat and drink.

How Many Types of Amino Acids Are There?

So far, more than 500 amino acids have been identified, but only 20 of these are commonly found in the human body. These are the ones that have direct correspondence to our genetic codes, which are involved in protein synthesis. Out of these 20, there are just nine essential amino acids, which include:

  • Histidine
  • Isoleucine
  • Leucine
  • Lysine
  • Methionine
  • Phenylalanine
  • Threonine
  • Tryptophan
  • Valine

These are all important in many functions of the human body, but they cannot be synthesised by the body; we have to get them from food.

Amino acids are classified into five groups:

  • Acidic: aspartic acid and glutamic acid
  • Basic: arginine, histidine, and lysine
  • Hydroxylic: serine and threonine
  • Sulphur-containing: cysteine and methionine
  • Amidic: asparagine and glutamine
  • Aliphatic: alanine, glycine, isoleucine, and leucine
  • Aromatic: phenylalanine, tryptophan, and tyrosine
Educational chart with all the common amino acids represented with color coded side chains

Examples of Amino Acids

Amino acids have corresponding genetic codes in our DNA. The DNA parts that are activated specify the protein to be synthesised by directing the types and sequence of amino acids that will form a polypeptide chain.

The gene expression, however, is indirect because the messenger RNA (mRNA) has to carry the specified codons to be transcribed by the transfer RNA (tRNA) on the ribosomes. Ribosomal RNA or rRNA are the ones that form the ribosomes.

Each codon, or combination of three nucleotides (DNA codes), can specify an amino acid. The way these are combined in a polypeptide chain is determined by the way the codons are activated in combination or in succession with other codons that correspond to a gene.

Here are examples of the nine essential amino acids and their uses:

  • Phenylalanine (Phe): Phe is important in the production of various brain chemicals, such as dopamine. It’s also essential in the synthesis of some enzymes.
  • Valine (Val): This is involved in the synthesis of muscle proteins and other tissues. It’s also important in producing energy.
  • Threonine (Thr): Threonine helps form structural proteins, such as collagen and elastin, which support connective tissues. It also helps maintain a healthy immune system.
  • Tryptophan (Trp): Trp is important in the synthesis of serotonin, a type of neurotransmitter that regulates sleep and emotions.
  • Methionine (Met): This amino acid supports various bodily functions, such as tissue growth and metabolic processes. It also facilitates the absorption of essential minerals, like zinc.
  • Leucine (Leu): Leucine is important in maintaining muscle health. It also helps to regulate our blood sugar. 
  • Isoleucine (Ile): This has a role in the cellular respiration of the skeletal muscles. It also helps maintain the efficiency of the immune system and participates in the synthesis of haemoglobin.
  • Lysine (Lys): The production of many enzymes and hormones depends on lysine, which also helps maintain our immune systems.
  • Histidine (His): Histamine production is dependent on histidine, and helps regulate sleep, sexual function, and the health of our nerve cells.

Are Amino Acids Important?

Approximately 20% of the human body is protein. Protein is present in all the cells. The skeletal muscles, the internal organs, hormones, enzymes, the blood, the immune system’s antibodies, the skin, and other parts of the body all have amino acids, either as their main constituents or as part of their structures. 

In other words, the human body cannot function properly if it’s deficient in one or more amino acids, especially when it comes to the essential ones. Various physiological functions, metabolic functions, immune functions, and reproductive functions are adversely affected when we’re deficient in amino acids.

Do Amino Acid Supplements Work?

Many athletes, particularly bodybuilders, take amino acid supplements. Typically, they take branched-chain amino acids. These supplements may help alleviate several conditions, especially after strenuous physical activities related to sports.

Amino acid supplements can:

  • Help muscle growth and repair
  • Lessen muscle pain
  • Alleviate fatigue due to exercise
  • Prevent the muscles from wasting away

Amino acid supplements can also help treat some medical conditions such as:

  • Loss of appetite
  • Tardive dyskinesia symptoms
  • Liver cirrhosis hepatic encephalopathy
  • Several types of brain disorders
  • Autism spectrum disorder
  • Diabetes

It’s important to talk to your GP before you take any health supplements.

Supplements spilling from a bottle on a table with two spoons of protein powder in the foreground

What Foods Contain Essential Amino Acids?

One or more of the nine essential amino acids are present in almost all the foods we eat. However, there are some food products that are particularly rich in them. Obviously, foods that are high in protein are also high in amino acids. Here are some of them:

  • Red meat, such as beef 
  • Poultry
  • Various types of seafood, such clams, squid, and fish
  • All dairy products, including milk, yoghurt, and cheese
  • Soybean-based products, such as tofu


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