What are Amino Acids?
Amino acids are the essential building blocks of proteins. When we eat protein-containing foods, it is essentially the amino acids and sufficient nitrogen that we are looking to obtain.
For this reason – and particularly for anyone following a predominantly plant-based diet – it’s a good idea to have some knowledge and appreciation of the different amino acids.
There are around 20 different amino acids that are commonly found within both plant and animal foods. However, nine of them (the essential amino acids) are of particular importance, as explained in this post.
Amino Acid Classification
Of the 20 amino acids, 9 are essential and must be obtained from our diet. Amino acids can be either:
- Essential – the body CANNOT produce these, so we must obtain them from our food.
- Conditionally essential – the body usually can actually produce these in sufficient amounts, but under certain conditions these amino acids may become essential.
- Non-essential – the body can produce these – fantastic!
It’s important to remember that we need to obtain the essential amino acids from our habitual food intake. The remaining amino acids our body can make on its own – as long as sufficient nitrogen is provided from the diet – as you will see in my diagrams below, all amino acids contain nitrogen.
So Which Amino Acids are Essential?
♦ Essential Amino Acids – It is absolutely necessary that we obtain these from our diet, as these cannot be made by the body.
- Valine – Contains a branched side chain (BCAA)
- Leucine – Contains a branched side chain (BCAA)
- Isoleucine – Contains a branched chain (BCAA)
- Lysine
- Methionine
- Phenylalanine
- Threonine
- Tryptophan
- Histadine
♦ Quick mention – Histadine is not always cited in lists of 8 essential amino acids. A complete list of all 20 amino acids is given at the end of this blog post.
The Structural Composition of Amino Acids:
All of the amino acids contain:
- a nitrogen containing ‘amino group’ (shown in blue)
- a carboxyl containing ‘acidic group’ (show in red)
- and a uniquely wonderful side chain – specific to each individual amino acid(pink)
So, it is these side chains that make each amino acid really special. For example, in the case of the simplest amino acid glycine – the side chain is a simple hydrogen – circled in pink 🙂
Glycine
If you compare this to the amino acid alanine, below, you can see how the side chain begins to differs between the amino acids.
Alanine
Branch chain amino acids (BCAA’s)
The core backbone structure is the same for all amino acids, including the branched chain amino acids valine, leucine and isoleucine. Again, you can see the nitrogen containing amino group in blue, and the acidic carboxyl group, shown in red. It is the wonderfully unique side chains – circled in pink – that differ, as illustrated below.
Valine
Leucine
Isoleucine
Amino Acids and Protein Facts:
- Amino acids link in polypeptide chains to form proteins.
- The amino group (shown in blue) of one amino acid reacts with the carboxyl group (shown in red) of another amino acid – in a condensation reaction to form a peptide bond. This is how the basic structure of proteins are formed.
- In this way, the simplest proteins are made up of chains of amino acids.
- When we talk about protein foods – it is really the individual amino acids that are most important.
Complete List of all 20 Amino Acids:
♦ Essential Amino Acids – It is absolutely necessary that we obtain these from our diet, as these cannot be made by the body.
- Valine – Contains a branched side chain (BCAA)
- Leucine – Contains a branched side chain (BCAA)
- Isoleucine – Contains a branched chain (BCAA)
- Lysine
- Methionine
- Phenylalanine
- Threonine
- Tryptophan
- Histadine
Note: Histadine is not always cited in lists of essential amino acids.
Selenocysteine is sometimes cited as the ’21st’ amino acid – but I have not included it in my core list of 20 amino acids.
♦ Conditionally Essential Amino Acids
The remaining amino acids listed below, can be synthesised by the body, and so are loosely described as non-essential – or conditionally essential amino acids. Although the body can produce these amino acids, under certain circumstances the body may be unable to produce sufficient amounts (for example during trauma, stress, infection and critical illness) where demand for these amino acids often exceed the body’s ability to produce sufficient amounts.
10. Cysteine – can be synthesised from the essential amino acid methionine
11. Tyrosine – can be synthesised from the essential amino acid phenylalanine
12. Arginine
13. Glutamine
14. Glycine
15. Proline
16. Asparagine – often classified in group below as non-essential
17. Serine – often classified in group below as non-essential
♦ Non-Essential Amino Acids
18. Alanine
19. Aspartic Acid
20. Glutamic Acid
This is the first in a series of posts which will be covering protein and amino acids in more depth.