Amino Acid Structure: Learn Definition, Basic Structure, Formula (2025)

Amino acid structure can be understood through its molecular and structural formula. In 1806, French chemists Louis-Nicolas Vauquelin and Pierre Jean Robiquet isolated a compound from asparagus that was subsequently named asparagine, the first amino acid to be discovered.

In 1953, Miller and Urey tried to recreate the conditions of primordial Earth in a flask.

They combined ammonia (\(NH_3\) ), hydrogen ( \(H_2\) ), methane (\(CH_4\)) and water vapours along with electrical sparks in the flask. In the flask, it was found that new molecules were formed, these molecules were identified as amino acids. In total, eleven amino acids were identified at that time. The term amino acid is actually short for α-amino [alpha-amino] carboxylic acid.

Let us learn more about amino acids, their structure, structures of common amino acids, molecular formulas and uses along with FAQs.

What are Amino Acids?

Amino acids are organic compounds that contain both an amino group(\(NH_2\)) and a carboxyl group (\(COOH\)) along with an organic side chain (R) unique to each amino acid. The organic side chain i.e. R groups are responsible for differentiating amino acids from one another.

Each amino acid has a central carbon atom, also called 𝛼-carbon, to which both functional groups i.e. amino group and carboxyl groups are attached. The remaining two bonds are fulfilled by a hydrogen atom and the organic side chain (R).

For e.g. Histidine(\(C_6H_9N_3O_2\)), Leucine (\(C_6H_13N_3O_2\)), Methionine (\(C_5H_11N_3O_2S\))

Amino acids are the building blocks of proteins. There are almost 20 amino acids in the proteins that we consume. Amino acids combine together to form a larger protein molecule.

Structure of Basic Amino Acid

Let us see the basic chemical equation and structure of the amino acid to get a better understanding –

Carefully look at the structure shown in the figure, we observe that the amino group (\(NH_2\)) and a carboxyl group (\(COOH\) ) are attached to the two ends of the central carbon atom. The other two chemical bonding are fulfilled by a hydrogen atom and the organic side chain (R).

It is common for other elements to be attached to the organic side chain. The side chain is unique for each amino acid, which makes it different from other amino acids. The versatility of the organic side chain is what helps in making diverse proteins that can be found in nature.

Structures of Common Amino Acids

There are hundreds of naturally occurring amino acids but out of these only 20 amino acids form a part of proteins in our body. These 20 amino acids are:

These amino acids are:

• Alanine – ala – A
• Arginine – arg – R
• Asparagine – asn – N
• Aspartic acid – asp – D
• Cysteine – cys – C
• Glutamine – gln – Q
• Glutamic acid – glu – E
• 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

These amino acids are further classified into two types – Essential Amino Acids & Non-essential Amino Acid

• Essential Amino Acids- Out of 20 amino acids, only 9 amino acids are essential amino acids. These acids are not synthesized by our bodies. We need to consume food containing these acids to obtain them in our bodies. These amino acids are- Leucine, Isoleucine, Lysine, Phenylalanine, Tryptophan, Histidine, Valine, Lysine and Theorine.
• Non-Essential Amino Acid – these acids are synthesized in our bodies and we do not need to rely on food for these amino acids. These are either produced by our body on its own or formed in the process of protein breakdown. Some non-essential amino acids are- Aspartic acid, Alanine, Asparagine, and Glutamic acid.

Molecular and Structural Formula of Amino Acid

The molecular formula of an amino acid is \(R-CH(NH_2)-COOH\). It consists of a basic amino group (\(NH_2\)) and an acidic carboxyl group (\(COOH\)) along with an organic R group (side chain) which is unique in each amino acid. This gives it both acidic and basic properties.

The structural formula for the molecules is:

In the image shown above, observe structure two and structure three. The grey sphere in the structure represents carbon atoms, the blue sphere represents an oxygen atom, nitrogen is represented by the light blue sphere and the light grey sphere represents hydrogen.

The central carbon atom or the 𝛼-carbon is attached to the carbon atom of the carboxyl group, nitrogen atom of the amino group, organic side chain R and a hydrogen atom.

The image shown above shows 20 amino acids, their classification on the basis of their structure and charge:

• Amino acids with electrically charged side chains i.e. the organic side chain (-R) of the amino acid carry either a positive or a negative charge on itself. For e.g.- Lysine, Glutamic acid.
• Amino acids with polar uncharged side chain i.e. the side chain(-R) group contains a polar molecule that is neutral or uncharged. For e.g.- Glutamine, Serine.
• Some special cases of amino acids such as Proline, the only amino acid where the side chain is connected to the protein backbone twice, forming a five-membered nitrogen-containing ring. Glycine is a unique amino acid because it contains hydrogen as its side chain rather than a carbon chain like other amino acids.
• Amino acids with hydrophobic side chains i.e. the side chain of these amino acids are water-hating or water-repelling species. For e.g. Valine, Alamine, Leucine.

Uses of Amino Acid

There are various uses of Amino Acids. Some uses have been listed in the points below:

• Amino acids are the building blocks of protein and are therefore used for the synthesis of protein in our body and laboratory.
• Human body uses amino acids for breaking down food, repairing body tissue and performing various other functions.
• Amino acids are also used as buffers in solutions as they are amphoteric and resist change in pH.
• Amino acids can be used for the production of glucose.

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