What is the Relationship Between Amino Acids and Proteins?

Lucy Bell-Young

by Lucy Bell-Young

17th November 2021

Amino acids and proteins have an integral relationship. Amino acids are traditionally defined as the fundamental building blocks of proteins, forming peptide bonds to build various types of them. 

This linear structure is called the primary structure of proteins, and usually forms α-helices and β-structures as their secondary structures. In turn, they can fold in several ways to form their tertiary structures.

Special genetic codes from the DNA are copied by mRNAs and carried outside the nucleus to be transcribed by the tRNAs in ribosomes. Amino acids are assembled into chains in a specific order based on the genetic instructions.

How Are Amino Acids Used in Protein Synthesis?

Without amino acids, proteins are impossible to synthesise. It would be like trying to cook a beef casserole without having any beef. 

A protein is composed of chains of amino acids that are either in their primary, secondary, or tertiary forms. The precise order or sequence that the amino acids are arranged in is determined by the genetic codes in the DNA or RNA inside the cell.

The genetic materials in a cell, whether DNA or RNA, contain the instructions on how to assemble proteins from amino acids. The latter are organic compounds that have an amino functional group (−NH+3), a carboxylate (−CO2) functional group, and a side chain, which uniquely identifies each type.

Proteins are assembled in ribosomes with the instructions transcribed by the tRNAs from mRNAs, which the latter copied from the DNA. Each amino acid has a corresponding codon, which is a three-nucleotide sequence, and is summoned into the ribosome to be stitched with other amino acids based on the precise sequence of codons, as in the illustration below:

Diagram of how proteins are assembled in ribosomes

What is the Role of Protein?

Approximately 20% of the adult human body is protein by weight. Each cell also contains proteins of various types. The synthesis of a particular kind is switched on and switched off depending on the needs of the body, such as immune response. Protein synthesis happens all the time in various cells.

Proteins have various roles, including as: 

  • Enzymes
  • Hormones
  • Antibodies
  • Storage proteins
  • Contractile proteins
  • Structural proteins

Many biological functions would not be possible without proteins. Most of the biochemical reactions in the human body, including digestion, aerobic respiration, and tissue repairs, are mediated by enzymes. These are continually produced by the body in response to internal and external stimuli.

Just like enzymes, many other proteins are only ramped up in production in the presence of stimuli such as infections, which cause the body to deploy and activate an army of immune cells.

Protein synthesis is an ongoing process that all cells do. It maintains the structure and functions of an organism at various levels:

  • Cells
  • Tissues
  • Organs
  • Organ systems
  • The whole multicellular organism

How Many Different Kinds of Amino Acids Make Up Proteins?

As of  2020, scientists have identified more than 500 naturally occurring amino acids. However, only 22 of these are found in most organisms and are genetically coded.

Human DNA only codes for 20 amino acids to form all the proteins that the body needs. Out of these 20, only nine are considered ‘essential’. This is because our bodies cannot make them, and they must instead be derived from the food we eat.

Below is a list of the 20 amino acids found in the human body along. The nine essential amino acids are highlighted in bold:

  1. Alanine (Ala)
  2. Arginine (Arg)
  3. Asparagine (Asn)
  4. Aspartic acid (Asp)
  5. Cysteine (Cys)
  6. Glutamic acid (Glu)
  7. Glutamine (Gln)
  8. Glycine (Gly)
  9. Histidine (His)
  10. Isoleucine (Ile)
  11. Leucine (Leu)
  12. Lysine (Lys)
  13. Methionine (Met)
  14. Phenylalanine (Phe)
  15. Proline (Pro)
  16. Serine Ser (S)
  17. Threonine (Thr)
  18. Tryptophan (Trp)
  19. Tyrosine (Tyr)
  20. Valine (Val)

Amino acids have three functional groups: the slightly acidic amino group, the basic carboxyl group, and the side chain. See the generalised structure shown in the illustration below:

Diagram showing the generalised structure of amino acids

The side chain gives a unique identity to a particular amino acid. It also determines the polarity of the amino acid. Aside from the side chain, amino acids can also be classified based on:

  • Charge: It can either have a positive or negative charge
  • pH level: It may either be basic or acidic
  • Solubility in water: This depends on the polarity; it’s only soluble in water if it’s polar
  • Location of the core functional group: The locations are labeled as alpha- (α-), beta- (β-), gamma- (γ-), and delta- (δ-)

Is There a Difference Between Amino Acids and Proteins?

The obvious difference between amino acids and proteins is the hierarchical chemical composition. Proteins are composed of amino acids and not the other way around. The chemical and physical properties of a protein depend on the way its amino acids are arranged.

Even if two proteins are composed of the same types of amino acids, they can be very different, depending on how the amino acids are arranged in a sequence. At the same time, the properties of a protein also depend on its secondary and tertiary structure.

The proteins from the food that we eat are broken down into their constituent amino acids during the digestion process. They are again reconstituted into different types during the process of protein synthesis.


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