Essential amino acids cannot be synthesized by the human body in sufficient quantities and must therefore be obtained from food. Non-essential amino acids can be synthesized by the body from other amino acids or metabolic intermediates, so they do not have to be supplied directly in the diet.
This distinction is part of B1.2 Proteins and is assessed at both SL and HL.
Feature | Essential amino acids | Non-essential amino acids |
|---|---|---|
Production by the body | Cannot be synthesized in sufficient quantities | Can be synthesized by the body |
Dietary requirement | Must be obtained from food | Do not need to be obtained directly from food |
Biological importance | Required for protein synthesis | Also required for protein synthesis |
Dietary proteins are hydrolysed during digestion into amino acids. These amino acids are absorbed and enter the body's amino acid pool, from which cells build new polypeptides through condensation reactions. If an essential amino acid is unavailable, the body may be unable to synthesize particular proteins at the required rate, even when other amino acids are abundant.
Animal-derived foods often contain all essential amino acids in adequate proportions. Individual plant foods may contain relatively low quantities of one or more essential amino acids, so a varied vegan diet should combine different protein sources, for example, legumes and grains, to provide an adequate overall supply.
A common misconception is that “essential” means biologically more important. This is incorrect: both groups are necessary for normal protein synthesis. The term only describes whether the body can synthesize the amino acid in sufficient quantities.
Exam technique: For a command term such as distinguish, state both sides explicitly: essential amino acids must be obtained from the diet because the body cannot synthesize enough of them, whereas non-essential amino acids can be synthesized by the body. Do not write that non-essential amino acids are unnecessary.
